The objective of this project was to thoroughly investigate factors related to alfalfa stand longevity in Montana. Twelve alfalfa fields were monitored over three years for the incidence of foliar and root diseases, arthropod pests, and crop management practices related to stand mortality. Particular emphasis was placed on evaluating the prevalence and severity of several new or unfamiliar pests in Montana, including the clover root curculio (CRC), alfalfa mosaic virus, and brown root rot. Crop management and insecticide trials were conducted to evaluate their impacts on CRC, other pests and alfalfa productivity. Numerous outreach activities were initiated through this project.
The objectives of this project were to investigate numerous biological and management practices that impact alfalfa persistence in production systems in Montana. Longer, productive alfalfa stands are desired by producers, however critical management steps may be required, and there may be some inherent limitations due to pest populations and interactions. Very little is known about the relationships among CRC feeding damage and prevalent root and crown rot pathogens that limit alfalfa stand longevity in Montana. Optimal alfalfa stand persistence will be beneficial to alfalfa producers to sustain stable hay production, and minimize economic and system risks. This multi-year WSARE project was particularly suited to monitor alfalfa stand and pest dynamics for three years post-establishment.
Alfalfa is the major forage crop grown in Montana with over 1.5 million acres harvested annually since 2000 (NASS, 2008 http://www.nass.usda.gov/Statistics_by_State/Montana/index.asp ). A majority (>90%) of all hay produced in Montana is fed on-site by producers to support the state’s $1.1 billion livestock industry. Alfalfa production in Montana is divided between almost equally between irrigated (51%) and dryland/rainfed (49%) production, with average annual yields of 3.30 and 1.04 tons per acre, respectively (NASS, 2008). At these fairly low production levels and with significant alfalfa renovation and re-establishment costs (>$150 per acre) most hay growers attempt to maintain alfalfa stands for as long as possible. Alfalfa provides a significant pasture base for livestock producers in the late fall and early winter in the northern Great Plains. Further, with very little commercial hay production in Montana, alfalfa stand productivity and longevity are critical issues identified by livestock producers, Extension agents and agri-business personnel.
Alfalfa stand longevity is influenced by many factors in Montana. The establishment of a healthy and vigorous stand in the year of seeding is crucial to long-term yield and persistence. Following the establishment year, alfalfa yield and longevity are affected by crop management practices, soil-borne pathogens and disease complexes, arthropod pests and winter injury. Agronomic recommendations and evaluations by universities and agricultural Experiment Stations (AES) are key to assisting producers adapt best management practices for alfalfa production.
In Montana, alfalfa is grown in diverse conditions and production scenarios- dryland or irrigated, with various annual crop or perennial grass mixtures, and with hay harvest often combined with fall and winter livestock grazing. Alfalfa is often planted with an annual “nurse” or “companion” crop. This traditional practice was recommended across the U.S., particularly in areas prone to erosion or high winds. Oat or other cereal grains provided some level of grain or forage production during the year of alfalfa establishment. In many regions including the majority of Montana irrigated alfalfa production, the use of nurse crops declined with the advent of modern herbicides. In the 1970’s Baldridge (cited in Dixon et al. 2005) monitored irrigated alfalfa yields of alfalfa stands that were planted in monoculture (with and without pre-plant Eptam herbicide) or with barley and spring wheat nurse crops grown for grain near Huntley, MT. Alfalfa hay yields in the fourth production year were 13, 23, 16, 22 and 14% lower for stands planted with no pre-plant herbicide, barley (6-inch rows), barley (18-inch rows), spring wheat (6-inch rows) and spring wheat (18-inch rows). Weeds and annual crops interfere with alfalfa establishment and long-term performance, and based on this and similar trials the Montana AES (MAES) recommends that producers avoid nurse crops unless absolutely necessary. If a nurse crop is used, the annual crop seeding rates should be reduced, row spacing (wider) and orientation (at an angle or perpendicular to alfalfa rows) should be modified, and harvest as forage to remove the competitive effect. Despite these recommendations, nurse crops are still widely used in Montana, particularly on dryland.
Across most of the U.S., alfalfa is grown in monoculture stands, however in the northern Great Plains, perennial grasses are widely planted in mixtures with alfalfa. In Montana, the predominant species include meadow bromegrass and orchardgrass under irrigated or high-rainfall conditions, and numerous “wheatgrasses” in dryland environments such as crested wheatgrass and intermediate wheatgrass. The use of mixed stands is practiced for a variety of reasons – the grasses are considered to aid in first-harvest windrow drying time, mixed hays provide adequate nutrition for overwintering beef cattle, mixed hays have secondary markets for beef or horse hay, the grasses allow for fall or winter grazing with reduced concerns for bloat and alfalfa crown damage, and frequently the mixed stand is considered as “pasture” in later years to extend its longevity prior to renovation. Alfalfa-grass mixed stands provide some particular challenges (few herbicide options), and limited information is available about the impacts of grasses on alfalfa stand dynamics and pest interactions in Montana.
Cultivar selection is an important step for producers to optimize the adaptation, production and longevity of alfalfa in Montana. The MAES-Montana State University system routinely publishes alfalfa variety trial results from both irrigated and dryland research centers. Alfalfa requires an appropriate “hardening” period during the autumn to store root carbohydrates and proteins for optimal winter survival and longevity. In previous unpublished research in irrigated trials in Montana, it was found that harvest (either second or third cut) between September 1 and 15 was more injurious to subsequent alfalfa production than harvest in early August or October. Likely, these dates coincided with low root reserves and an inadequate period for their replenishment. An accepted winter survival test to compare alfalfa cultivars is based on space-planted alfalfa performance following an “intensive” (mis-timed) harvest in the previous autumn (http://www.naaic.org/stdtests/wintersurvivalnew.htm). Typically, dormant alfalfa cultivars (Fall Dormancy Ratings 1 – 4, or Winter Survival Ratings 1 – 3) are widely adapted in Montana.
In addition to adaptation and forage yield potential, alfalfa growers should choose varieties with genetic resistance to several disease and arthropod pests. For many soil-borne diseases, the only economic and effective control measures are crop rotation and varieties known to have multiple pest resistance. Based on samples evaluated in the MSU-IPM Diagnostic Laboratory and experienced pathologists, the diseases in this category include bacterial wilt, Verticillium wilt, Fusarium wilt, Phytophthora root rot, and Aphanomyces root rot. Occasional infestations by the stem nematode, northern root knot nematode, pea aphid and spotted alfalfa aphid are reported by the lab, and resistant varieties are available for these pests.
Several alfalfa pest problems occur variably in Montana for which there are presently no resistant cultivars. These include the alfalfa weevil (which frequently requires insecticidal control) and diseases such as the crown and root rot complex (Fusarium and other fungi spp.), common leaf spot and spring black stem. Two pests in Montana that may contribute significantly to alfalfa stand morality – brown root rot and the clover root curculio – have been confirmed in the state, however their prevalence and severity are not known. Brown root rot (caused by Phoma sclerotioides) has been recently identified in Montana by the MSU IPM Diagnostic Lab, and is of particular concern because of the long rotation intervals (4+ years) required before re-establishing alfalfa.
The clover root curculio (CRC) Sitona spp. is found throughout the United States and southern Canada. The CRC feeds on many clovers (Trifolium spp.), alfalfa, Kentucky bluegrass, soybeans, cowpeas, and other legumes. The CRC adults feed on foliage, however the larvae cause the primary damage associated with this pest. Larvae burrow into the soil, feeding on alfalfa nodules and lateral roots as the instars progress (Tan and Hower 1991). Plant damage that has been reported includes interference of stand establishment, reduced plant vigor, and lower forage yield and stand longevity. The open feeding wounds on lateral roots and the taproot may provide entry by numerous soil-borne pathogens. The incidence and severity of CRC root feeding damage has often been correlated to increased incidence of root and crown rot pathogens (Leath and Hower 1993, Kalb et al. 1994), particularly Fusarium spp.
Field surveys in Virginia indicated that CRC was one of the most common and injurious alfalfa pests, and root rot was often associated with CRC-damaged roots (Underhill et al. 1955). Godfrey and Yeargan (1989) reported that CRC feeding reduced stand density only during the first year of the stand. In contrast, Hower et al. (1995) found repeated and continued CRC damage to alfalfa stand yield, quality, and persistence.
The CRC originated in Europe, and the insect’s life cycle varies in different regions in the U.S. In Virginia (Underhill et al. 1955) and Maryland (Phillips and Ditman 1962), it was found that most CRC eggs were laid in the fall, however other sources indicate spring or season-long egg laying. The CRC adults migrate short distances from infested fields or other suitable areas, and can repeatedly infest an alfalfa field over its life. Survival and damage by CRC larvae varies depending on soil conditions. Pacchiolo and Hower (2004) reported that CRC larvae survival and feeding damage were related to soil texture. Moist silt-clay loam contained cracks larger than 1.0 mm which enabled increased access of CRC first instars to feed on alfalfa root nodules compared to sandy loams. The sandy loams had smaller pore spaces, and it was postulated that the sand particles were abrasive to the cuticles of the CRC larvae (Pacchiolo and Hower, 2004).
The incidence and severity of CRC are not currently well understood in Montana. Many alfalfa plant samples submitted to the MSU-IPM Diagnostic Lab have significant tap root damage and girdling caused by feeding patterns characteristic of the CRC. In recent monitoring trials, adult Sitona spp. were recorded across Montana between mid-March and early October (Fig. 1). High adult CRC numbers (>25 per sweep) in September in Gallatin County (western Montana) would indicate egg laying in the fall, however more observation is needed. During identification of CRC adult species collected from sweep net samples, we found that the majority (61%) were S. hispidulus, 26% S. flavescens, and 12% S. lineelus. Although the recognized CRC according to the Entomological Society of America and Canada, is S. hispidulus, Bright (1994) reported that other Sitona species including S. flavescens and S. lineellus can cause economic damage to alfalfa. Therefore, in this report we refer to the CRC as the complex of these three Sitona species.
This project consisted of four activities: a) intensive monitoring of alfalfa stands established in 2004 for productivity and pests in diverse Montana production systems during 2005-2007, b) measure and demonstrate the impacts of annual “nurse” crops on establishment and productivity of dryland alfalfa, c) evaluate cultivar and harvest management effects on alfalfa production and stand dynamics, and d) evaluate timing and impacts of insecticide application on CRC root feeding symptoms. All trials were coordinated by the primary investigators, Drs. Sue Blodgett and Dennis Cash, with sample collection and data analyses by trained research associates Rebecca Baril and Cecil Tharp. Significant assistance was provided by Dr. Mary Burrows, Extension Plant Pathologist, and numerous producers and county Extension faculty.
A. Statewide Monitoring: Fifteen alfalfa fields were identified by Extension agent participants as trial sites in 2005. The field sites were selected on the basis of stand age (all were established in 2004), access, interest by the producer cooperators, and the availability of field history and production records during crop growth. Detailed alfalfa production records were collected by annual producer interviews with Extension personnel and a mid-term survey (Appendix 1). In 2006, three field sites were discontinued due to stand failure or the lack of personnel for sample and data collection. The locations of the 12 field sites monitored in 2005 through 2007 in nine Montana counties are shown in Fig. 2.
The field sites ranged from 8 to 97 acres (Table 1), and the participating growers manage a total of 5721 acres of alfalfa hay production (Appendix 1). A majority of the hay produced by the 12 cooperators is produced for on-site cow-calf production, with limited amounts fed in feedlots or marketed for dairy or horses. Eight of the monitored sites are irrigated (7 by flood, 1 by sprinklers) and four are dryland. Three of the irrigated stands were alfalfa-grass mixtures (orchardgrass or meadow bromegrass), and the other irrigated stands were monocultures of alfalfa. Further, three producers applied insecticides for the control of alfalfa weevil in all years or 2006 and 2007. Based on locations, soil types, field history and crop management practices these 12 sites appear to be a representative cross section of Montana alfalfa production systems.
During the growing season, Extension agents and producers collected bimonthly insect samples from all alfalfa fields in 2005-2007. The samples were obtained by a 25-sweep collection with a standard 38 cm2 net. The arthropods collected were placed in sample vials and shipped immediately to the laboratory, where they were stored in a freezer prior to enumeration and identification. Field samples were collected by project coordinators each year during spring green up and in the autumn. Data included stand counts and evaluation of CRC feeding damage, foliar diseases and root or crown rot symptoms. Stand density (including crop mixtures and weeds) was evaluated by counting stems in 10 random 0.1m2 ring samples. Plant and pest evaluations were obtained by excavating 10 random plants. Individually-labeled plants were transported to the laboratory and evaluated visually for stem number per plant and the presence of foliar insect damage, alfalfa mosaic virus, spring blackstem, CRC root feeding damage, and the incidence of crown and root rot symptoms.
In 2005 and 2007, leaflet samples from all plants were evaluated for AMV infection using the DAS-ELISA technique (Agdia Inc., Elkhart, IN). Symptoms of CRC damage were visually appraised on a 0 to 5 scale (Kalb et al, 1994) based on the percentage of individual roots with feeding damage: 0 (no damage), 1 (1-10%), 2 (11-35%), 3 (36-65%), 4 (66-90%) and 5 (90-100%). Data for CRC recorded at each sample date included the incidence (percentage of 10 plants with a CRC score of 1 to 5) and average severity index (ASI = mean CRC damage score for the 10 plants). In 2005 and 2006, crown and root rot incidence were recorded, however in 2007 all roots and crowns were scored individually on a 0 to 5 scale: 0 (no rot), 1 (slight to 10% area infected), 2 (11-30%), 3 (31-60%), 4 (61-100%) and 5 (dead plant). Specific notes on any root rot symptoms adjacent to CRC feeding injuries and other comments were maintained on an individual-plant basis. In 2007, infected root or crown tissues from all plants were maintained from the spring and fall samples for detection of P. sclerotioides (causal agent of brown root rot) with DNA test kits. (A complete description of the P. sclerotioides testing procedure is in the Appendix 2).
In addition to plant and insect sampling, soil, climate and detailed producer records of fertilizer, pesticides, irrigation and harvest were monitored. Soil texture and pH were evaluated for all sites. In 2005, daily precipitation and temperatures from nearby weather stations were used. In 2006 and 2007, on-site climate was monitored in all fields using HOBO data loggers (Onset Computer Corp., Pocasset, MA).
All crop and production data were summarized in annual reports, and maintained through 2007 for comprehensive analyses. Summary analyses for alfalfa stand density (both by stems per plant and stems per foot) and reported forage yield were evaluated by regression. Predictive models to determine when to renovate an alfalfa stand are used in other regions (Undersander et al. 1998), however have not been evaluated in Montana, and particularly on dryland alfalfa. All data for disease and CRC damage (incidence and ASI) were summarized over time.
Categorical contrasts of dryland vs. irrigated, monoculture alfalfa vs. alfalfa-grass mixtures (all in irrigated stands), and insecticide applied vs. no insecticide (all in irrigated stands) were calculated for all variables by t-tests (two-sided, unequal variance). Contrasts involving stand mixtures or insecticide application were likely confounded due to sites combining these practices (Table 1), however the analyses were performed to evaluate trends. Five producers planted alfalfa with a nurse crop (cereal or millet) that was harvested for hay or grain. No contrasts were calculated for the practice of planting alfalfa with a nurse crop due to limited site numbers and confounding with other categories. There are limitations to the inferences that can be made for many of the traits observed due to the effects of confounding, differences among cultivars, soil types, producer management and other factors. Further, with only 10 samples per site-period, accuracy of measuring some variables may be suspect. However, comparisons of trends across the diverse monitoring sites were of interest, so conservative tests and interpretations were made. Regression analyses were used to explore other relationships of interest.
B. Nurse Crop Trial: In many regions in the U.S. alfalfa has traditionally been planted with annual nurse crops. This practice remains fairly common (five producers in the statewide monitoring trial), particularly on dryland in Montana. Very few studies have been conducted to compare the impact of nurse crops that are harvested for hay or grain in a dryland environment.
A replicated trial was established at the Central Montana Agricultural Research Center near Moccasin, MT in April 2004. (Specific site and climate details for this site are available at: http://animalrangeextension.montana.edu/Forage/forage_pub.htm ).
The trial consisted of ‘Shaw’ alfalfa (5 pounds per acre) seeded alone and in various factorial combinations of treatments seeded in-furrow or perpendicular to the alfalfa. These included (low and high seeding rates of nurse crops in pounds per acre shown in parentheses): barley harvested for grain (25, 50), barley harvested for hay (20, 40), spring wheat for hay (20, 40) triticale for hay (20, 40). The trial was established as split-plot design, with the main plots seeded in-furrow with or perpendicular to the alfalfa. Plots were 5 x 12 feet, with 12-inch drill row spacings. All factorial treatment combinations were replicated twice, and alfalfa seeded alone (control) had eight replications for a total of 40 plots.
In 2005, forage yields were determined on all plots with a self-propelled sickle plot harvester. Based on 2005 results and due to a personnel shortage at the center, forage yields were not obtained in 2006 or 2007. Stand counts (as described in Statewide Monitoring above) and crop heights were monitored in the spring and fall from 2005 through 2007. All data variables were analyzed by ANOVA.
C. Cultivar and Harvest Management Trials: No trials have been conducted in Montana to determine the potential variability among alfalfa cultivars for susceptibility to CRC root feeding injury or CRC-root pathogen interactions. In October 2003, a root pruner was used to excavate alfalfa roots in the MAES irrigated variety trials at Bozeman (Gallatin County) and Huntley (Yellowstone County), MT. These replicated trials were planted in 2000, and consisted of the same 18 cultivars at each site. Forage yields were monitored for four years prior to the termination of the trials. At Bozeman, all plants excavated within the area pruned (5 square feet) were evaluated, and 10 plants per plot at Huntley were scored. Roots were scored for the incidence and severity of CRC feeding damage and crown rot symptoms as previously described. A description of the cultivar testing program and these particular sites is at: http://animalrangeextension.montana.edu/articles/forage/main-varieties.htm.
Prior to this WSARE project, several replicated winter survival trials had been conducted at MSU near Bozeman, MT. New replicated trials to evaluate the impacts a poorly-timed late summer harvest date on alfalfa yields and stand decline were established in 2000, 2001 and 2002. These trials were superimposed on the existing irrigated variety trials at Bozeman, MT. All plots were managed identically for the first and second harvests. For the third harvest, the paired plots received differential harvest dates – half were harvested on September 1, and the other half were harvested in mid-October. Forage yields were obtained with a plot harvester, and forage yield subsequent to the third harvest treatment was used as an indicator of treatment effects. During the autumn of 2003 and 2004 (end of fourth production year of the trials planted in 2000 and 2001, respectively) a root pruner was used to excavate all plots for final stand counts and to examine root and crown disease symptoms and CRC root damage (described previously). Assistance was provided by this WSARE grant for the root evaluations in 2004. Data for all variables were analyzed by ANOVA to determine differences among cultivars and harvest management treatments.
D. Insecticide Trials: The potential for applying topical insecticides to reduce CRC root feeding damage was investigated in four trials in irrigated hay production fields. Two initial trials (Amsterdam 1 and Amsterdam 2) were established in fields that were planted in 2002 and 2004, respectively. During the spring of the one-year-old stands (2003 and 2005), replicated 20 x 50 foot plots were assigned as control or carbofuran (Furadan 4F at 1 pound active ingredient per acre) treatments. The Amsterdam 1 site was sprayed once on May 16, 2003 (r=8) and sampled on May 4, 2004. The Amsterdam 2 site was sampled on May 6, 2005 immediately prior to insecticide application (all plants had very initial low CRC scores, 0 to 1). Roots samples from all plots (r=4) were excavated. At the conclusion of both trials, 10 plants were dug from all plots and scored for CRC damage as previously described. These trials were short-term due to the producers’ crop rotation needs.
Two multiple-application insecticide trials were established near Huntley (planted in April 2003) and Bozeman, MT (planted in 2005). Treatments in these trials were control plots, and Furadan 4F applied every fall (including year of planting), every spring, and every spring and fall. Prior to spring and fall insecticide applications, 10 plants were excavated and evaluated for CRC root feeding damage and root symptoms as described previously. All data were evaluated by ANOVA.
A. Statewide Monitoring: A large amount of data were compiled from the 12 producer field sites. Arthropod populations: Significant numbers of alfalfa weevil larvae, pea aphid and other insect pests were found at some sites during the growing season, however rarely above established economic thresholds for control (Table 2, Appendix Table 2). Producer awareness about the losses of first-harvest alfalfa due to alfalfa weevil larvae has increased in Montana during the past decade. Interestingly, two growers applied insecticide in all three years and one grower in 2006 and 2007, despite all being below the threshold for alfalfa weevil larvae.
Among beneficial arthropods, there were significantly higher (P< 0.10) ladybird beetle populations in irrigated fields and monoculture alfalfa stands than in dryland or mixed stands, respectively (Table 2). There were higher (P< 0.10) pea aphid numbers in irrigated fields than in dryland stands, which could explain the differences in ladybird beetle populations in irrigated fields. Populations of plant bugs and alfalfa caterpillar were higher P< 0.10) in monoculture alfalfa stands than in alfalfa-grass mixes (Table 2).
Across years, three alfalfa fields that were sprayed with insecticides (2005 – 2007 or 2006 – 2007) for alfalfa weevil larvae control subsequently had reduced (P< 0.10) numbers of CRC adults and pea aphid compared to untreated fields (Table 2). Insecticide application tended to reduce CRC adult numbers each year (NS), and across years (Table 3). Interestingly in the insecticide-treated fields, there were no significant reductions in the number of alfalfa weevil larvae and adults (target pest) or other pest or beneficial arthropods as compared to the untreated fields. The temporal and spatial variability of insect populations among these 12 sites preclude many global conclusions, however the trends noted will be of interest for producers of dryland or mixed stands of alfalfa-grass.
The CRC was detected at all sites, though not in all years at each site (Table 3). Fairly high numbers were noted in Phillips County (site 10) in all years. This is the first report of widespread distribution of the CRC in Montana. All cooperators in this project manage large acreages of alfalfa, so infestations of new stands by the CRC would appear to be fairly common across these counties.
All of the notable foliar and root diseases in Montana were observed in the statewide monitoring project (Table 4).
Alfalfa mosaic virus (AMV) has not been widely monitored in the state, but was confirmed by the DAS-ELISA tests in all fields except site 2 (Rosebud2). Average infection by AMV approached 20% by the end of 2005 (Table 4). By the completion of the trial in 2007, AMV infection was confirmed in 56% and 10% of the plants in irrigated and dryland fields, respectively (P< 0.10). The pea aphid is a vector for AMV, so these differences likely reflect the higher aphid numbers in irrigated alfalfa fields. The foliar symptoms are quite classic, however there was not much agreement in visual observations and results from the DAS-ELISA test (Table 5). For plants with visual AMV symptoms, DAS-ELISA confirmed that 20 to 65% of the plants were AMV-infected. Conversely, 14 to 30% of visually asymptomatic plants were infected with AMV according to DAS-ELISA. These results differ from those of Martin et al. (1997), who reported that 100% of all symptomatic red clover plants infected with AMV under laboratory conditions tested positive for AMV, and all symptomless plants tested negative.
These data are the first statewide confirmations of AMV incidence across Montana. The virus is seed-borne and the majority of fields likely were initially contaminated with AMV through the planting of infected seeds. Once in the field, the virus spreads from infected plants to healthy plants by sap transmission or by plant fertilization, either through insect feeding or harvesting machinery. The insect most commonly associated with transmitting the disease is the pea aphid. Crop losses due to AMV are not well described, but forage yields in alfalfa are generally reduced due to reductions in nitrogen fixation and, and increased energy consumption through increased respiration.
Spring blackstem SBS was found at all sites, ranging from 34 to 93% incidence in the spring and 12 to 40% in the fall (Table 4). Spring incidence of SBS was generally higher in irrigated stands than in dryland stands, but this difference was only significant (P< 0.10) in 2005. The disease was present at similar levels in both monoculture alfalfa and mixed stands. This disease is widespread across Montana in the early summer, though losses to this disease are not clear.
Crown rot symptoms of alfalfa increased from 9% in Fall 2005 to 73% affected plants in Fall 2007, which is similar to previous evaluations in Montana. Average severity (ASI) of crown rot symptoms across the 12 sites was 1.80 in Fall 2007, which indicates low to moderate infection. There were no differences in crown rot incidence or severity among irrigated vs. dryland stands or monoculture vs. alfalfa-grass mixed stands (Table 4).
Root rot incidence increased from 21% in Fall 2005 to 85% in Fall 2005 (Table 4). The incidence of root rot symptoms was higher (P< 0.01) in irrigated stands than dryland stands in the Fall of 2005 and 2007, so it appears that irrigation impacts disease development by the root rot organisms. Average root rot severity (ASI = 1.45)) was low in Fall 2007, and there were no differences related to irrigation or stand types.
Clover root curculio (CRC) root feeding damage increased more rapidly over time than the crown and root rot symptoms (Fig. 3). Average incidence of CRC damage increased from 7% affected plants in Spring 2005 to 98% in Fall 2007 (Table 4). The incidence and severity of CRC were generally higher in irrigated stands than in dryland stands, however these differences were only significant (P< 0.10) for ASI in Fall 2005. Interestingly, grass-alfalfa stands tended to have higher incidence and severity (ASI) of CRC damage than monoculture grass stands, however these differences were not significant in all years. It is not known if the grasses in a mixed stand act as preferred hosts or beneficial habitat for CRC oviposition, or simply the reduced alfalfa density per unit area concentrates CRC feeding on fewer plants.
A further difference was noted in CRC root feeding damage in fields where insecticides had been sprayed to control alfalfa weevils. Insecticide-treated fields had lower (P< 0.10) incidence and severity of CRC feeding in Fall 2005 and lower severity in Spring 2006 than untreated fields, though these differences diminished by 2007 (Table 6). These CRC feeding damage results generally agree with the reduced CRC numbers in sweep samples following insecticide application (Table 3). The timing of CRC seasonal migration and egg laying in Montana are not clearly understood, and the efficacy of controlling adult CRC with insecticides is questionable. However these data indicated that insecticides or other control strategies may have potential for reducing damages from this pest.
Interactions of CRC with root diseases: The overall increase in crown rot, root rot and CRC damage indicated a positive correlation among these pests (Fig. 3). Leath and Hower (1993) reported a positive relationship among crown and root rot in alfalfa and the activity of CRC. Kalb et al. (1994) also found highly significant, positive linear correlations between CRC feeding predisposing alfalfa plants to more severe crown and root rot especially to Fusarium spp. In this statewide pest survey, 240 individual plants were scored for the severity of crown rot, root rot and CRC feeding damage in 2007. Regression analyses indicated that there were limited relationships in CRC feeding damage vs. root rot severity (R2 = 0.0135) or crown rot severity
(R2 = 0.000, Fig. 4). Many plants had severe root or crown rot symptoms independent of CRC feeding damage (Fig. 5).
These results contrast with those of previous reports (Leath and Hower, 1993, Kalb et al., 1994). The crown and root rot complexes in Montana have not been fully identified, but Fusarium spp. are routinely present in diagnostic samples received to MSU. Most of the cultivars evaluated in this trial have a high level of resistance to F. oxysporum, however resistance to other Fusarium spp. or other local root and crown rot pathogens is not known. The stands at the 12 Montana sites were monitored in the Spring and Fall through three years of production post-planting. Symptoms of crown rot, rot and CRC feeding damage were mild to moderate at the end of the trial, and perhaps more significant relationships between CRC and root disease symptoms would develop over time with more severe disease symptoms. However, at the termination of this trial there appears to be no evidence of a cause-and effect relationship between CRC feeding sites and increased root or crown rot disease development.
Soil texture and CRC: During this statewide pest survey, soil samples (0 to 15 cm cores) were obtained from the 12 sites and tested for texture, organic matter, pH and salinity. Regression analyses were computed with sand and clay contents compared with the average 2007 severity scores for crown rot, root rot and CRC feeding damage. CRC damage was negatively associated with sand concentration (R2 = 0.2632) and positively associated with clay concentration (R2 = 0.6118, Fig. 6). These data agree with the report by Pacchiolo and Hower (2004), and it appears that clay content is fairly predictive of potential CRC feeding damage. Alfalfa is grown on a large acreage in Montana with heavy-textured soils, so these results will be of interest to many producers.
Alfalfa yield and stand dynamics: Stands declined from an average of 10.9 plants per 0.1 m2 (Spring 2006) to 3.7 plants in Fall 2007 (Table 7). Irrigated stands had higher (P< 0.10) plant populations than dryland stands in Spring 2005 and in 2006, but these differences diminished by 2007. These data are similar to previous stand observations in Montana where stands declined from about 200 plants per m2 in the fall of the establishment year to about 50 plants per m2 in the third production year. Under ideal growing conditions and in the absence of pests, there is tremendous interplant competition that leads to significant plant mortality in a young alfalfa stand. Dryland stands are planted at lower seeding rates than irrigated stands because the rainfed environment will support a lower final alfalfa population. Stems per 0.1 m2 declined from an average of 55 in Spring 2005 to 32 in Fall 2007 (Table 7). Irrigated stands had significantly more (P< 0.10) than dryland stands in 2005, Spring 2006 and Fall 2007. Stem numbers per unit area (comparing spring to spring or second cutting to second cutting across years) typically remain fairly constant in the early years of an alfalfa stand. Stems per plant were variable, ranging from 4.8 to 11. The stems per plant and apparent decline in stem densities in this trial could reflect an interaction of sampling dates with environmental or management practices across the 12 sites evaluated. Alfalfa crown diameters increased from an average of 4.8 mm in Spring 2005 to 12.9 in Fall 2007 (Table 7). Crown diameters did not vary between irrigated and dryland sites, but alfalfa in grass-mixed stands had larger (not always significant at P< 0.10) crowns than monoculture alfalfa stands. These data reflect differential alfalfa root development rates in mixed stands. Annual hay yields of irrigated stands were 5.3 to 5.9 tons per acre, compared to 1.4 to 1.9 tons per acre on dryland (P< 0.10, Table 7). In 2005, alfalfa–grass mixed stands (6.0 tons per acre) had higher yields than monoculture alfalfa stands (4.8 tons per acre, P< 0.10), but over time these differences diminished. Percent weed cover varied considerably across sites. Dryland stands had higher weed populations than irrigated stands, but these differences were only significant in Fall 2005 and Spring 2006. The difference in weed populations in irrigated vs. dryland is interesting, however since all stands evaluated were planted in 2004, these results may strictly be related to the year of establishment. Producers planting dryland alfalfa always face considerable risks. Producers in this project used a variety of accepted crop rotation and herbicide strategies prior to alfalfa establishment. Only two producers (one irrigated, one dryland) used herbicides after planting, and clipping or haying during establishment is often fairly successful for weed control. At low production potentials, it is unlikely that dryland alfalfa producers will routinely invest in annual herbicide applications, so alternative weed control strategies are employed. Prediction models for of alfalfa yield: Several predictive models have been developed to estimate alfalfa yield based on plants or stems per unit area. These models are most useful for producers early in the spring to make the decision to terminate a stand that is not economically viable to maintain. Models to predict alfalfa yield based on stand density have not been evaluated in Montana. Data from the statewide monitoring trials were analyzed to determine the relationships between seasonal hay yield and spring densities of plants or stems per 0.1 m2. Prior to regression analyses, the plant data were converted to plants per square foot to compare with existing models, and for potential use by producers. Spring counts of plants per square foot provided poor prediction of seasonal yields, with R2< 0.03 for both dryland and irrigated stands (Fig. 8). The low relationships could be due to the limited numbers of samples (all three years of dryland stand data were included) or the young age of the stands. In previous unpublished research trials, yield predictions based on plants per unit area have not proven to be accurate in Montana, and are not applicable for dryland alfalfa. For example, ‘Ladak 65’ alfalfa has very broad crowns, and in many cases can sustain reliable forage yields with plant populations of one plant per square foot, as in this trial. Stem count in spring has been reported to be a good predictor of subsequent seasonal forage yield in Wisconsin by Cosgrove and Undersander in 1992 (cited in Undersander et al., 1998). In the 2005 through 2007 statewide monitoring sites, the University of Wisconsin model overestimated forage yield at dryland sites (Fig. 8). A new predictive equation from the Montana dryland data was developed (Fig. 8) with fair fit between stem counts per square foot and hay yield (R2 = 0.26). In the irrigated statewide data, only 2006 and 2007 were used due to extremely high stem counts at two locations (sites 5 and 6) in 2005. For irrigated sites, regression of yield on stem counts resulted in very poor fit. This is reflected by four irrigated site-years with seasonal yield of about 5 tons per acre that had spring counts of 12, 28, 57 and 77 stems per square foot (Fig. 8). From these results, it appears that existing models to predict alfalfa forage yield from stand density have limited applicability to Montana stands of less than four years in age. Likely, more research in older stands will be required to develop accurate prediction models. Dryland alfalfa yields were positively related to growing season precipitation in 2005 through 2007 (Fig. 9). The marginal relationship (R2 = 0.1117) could likely be improved by calculating precipitation from the previous autumn, however inadequate reliable data were available. Within a dryland site, annual hay yield is closely related to annual precipitation. These data evaluated across alfalfa stands suggest that other factors such as soil type, pests and grower management also impact alfalfa yield. B. Nurse Crop Trial: Dryland alfalfa stands at the Moccasin, MT site declined from an average of 11 plants per 0.1 m2 in the fall of the establishment year (2004) to 4.2 in 2007 (Fig. 10). Alfalfa seeded alone had significantly (P< 0.05) better stands in 2004 and 2005 than the average of all nurse crop treatment combinations, however these differences diminished for the duration of the trial (Fig. 10). Forage yields in July 2005 were affected by an interaction in companion crops and their seeding rates (Table 8). Alfalfa planted with spring wheat (high seed rate) harvested for hay had significantly higher yield in 2005 than alfalfa planted with hay barley (high rate) or barley for grain (high rate, Table 8a). Interestingly, alfalfa planted with nurse crops at high seeding rates tended to have higher alfalfa yields in 2005 than lower seeding rates, however this difference was not significant. In spring 2006, alfalfa stands planted with a nurse crop planted perpendicular to the alfalfa were superior (P< 0.05) to those planted in-furrow (Table 8b). There was an interaction of orientation with nurse crops which was likely due to differential slopes in the response. Statistical differences among planting orientation (in-furrow vs. perpendicular with alfalfa), nurse crops or monoculture vs. nurse crops (averaged over seed rates and orientation) were not detected for the majority of stand, crop height or weed measurements made for the duration of this study. From these data, it would be premature to conclude that nurse crops have minimal effects on dryland alfalfa establishment and longevity. This type of trial should be repeated over more dryland sites and planting seasons with collection of alfalfa yield data to be confident for grower recommendations. In the meantime, our current recommendations of planting nurse crops that are less competitive (wheat), planting the nurse crop at an angle or perpendicular to the alfalfa, and harvesting the nurse crop as forage would appear to be viable. Reduced seed rates of the nurse crops would also be more economical than high seeding rates. C. Cultivar and Harvest Management Trials: In 2003, replicated plots of 18 alfalfa varieties grown in MAES trials planted near Bozeman and Huntley, MT were evaluated for crown rot and CRC damage. There were significant differences among varieties for crown rot symptoms at Bozeman in 2003 (Table 9). The cultivar ‘4200’ (ASI = 2.29) had significantly lower crown rot ratings than six other cultivars at Bozeman. A majority of the 18 varieties were released since 1995, and are reported to have high levels of resistance to F. oxysporum and numerous root diseases http://www.alfalfa.org/pdf/NAFA%2007-08%20Varieties%20Leaflet.pdf, but there did not seem to be any correlation in this information and the crown rot symptoms we noted. ‘Ladak 65’ is the oldest cultivar tested in these trials. This variety (released in 1965) predates most of the standard tests for disease resistance. Only four cultivars tested had lower crown rot severity ratings than Ladak 65 (ASI = 2.84) at Bozeman. There were no differences among cultivars for CRC feeding damage at both locations or for crown rot at Huntley (Table 9.) Crown rot ratings among locations were correlated across locations (r= 0.428), and fourth-year forage yields were negatively correlated to crown rot severity at Bozeman (r= -0.428) and Huntley (r= -0.302). Across cultivars, average CRC damage at Bozeman (ASI = 4.55) was more severe than at Huntley (ASI = 3.25, P< 0.001). Although there were no differences among cultivars for CRC feeding damage, about 58 plants (of 5827) at Bozeman and 142 plants (of 720) at Huntley at CRC root damage scores of 1. These plants were selected for breeding purposes, and if CRC tolerance is a heritable trait, it should be possible to develop cultivars with increased tolerance. In the harvest management trials at Bozeman, 52 cultivars were evaluated under a regime to evaluate the effects of a poorly timed third seasonal harvest. Across the three trials, fourth-year and total alfalfa yields were significantly reduced by the September 1 harvest date (Table 10). The fourth-year forage yields (as a measure of cumulative treatment effects) of the intensive treatment were 39, 15 and 21% lower than resulted from the normal third harvest date in the 2000, 2001 and 2002 trials, respectively (Table 10). The 2000 trial received the intensive cutting treatment in the year of establishment (2000) and the two subsequent years, whereas the 2001 and 2002 trials had normal harvest management in their first year. The “intensive” harvest schedule imposed in the 2000 trial matches the protocol published to evaluate space-plants of cultivars for winter survival (http://www.naaic.org/stdtests/wintersurvivalnew.htm). Interestingly in these 2000 – 2002 trials, there were no significant differences among cultivars of known winter survival for differential yield effects; i.e. the poorly-timed harvest resulted in similar (NS) percent yield losses in all cultivars. Alfalfa stand density and root/crown biomass were reduced, and weed biomass increased as a result of the intensive late summer harvest treatment, although these effects were not always significant (Table 10). Many of the weeds were winter annuals that likely invaded the stands during the fall when there was adequate soil moisture and limited crop canopy. Interestingly, there were significant (P< 0.05) increases in the severity of crown rot and CRC damage in the intensively-harvested plots in the 2000 trial (Table 10). It is possible that the increased stress of alfalfa plants related to the harvest regime was responsible for the increased pest symptoms. This trial should be conducted again to determine if these results are repeatable, as there are no previously published reports of alfalfa cutting schedules impacting CRC feeding damage. It is clear that late summer harvest schedule impacts yield and longevity of irrigated alfalfa stands. Recommending a critical “no harvest” period is difficult because the decision is made well ahead of freezing conditions, which vary widely among years and locations in Montana. It is assumed that poorly-timed grazing by livestock and wildlife (deer, elk, antelope) would have similar effects. No data are available for dryland alfalfa, however if adequate summer rains resulted in significant regrowth for a second cutting, it is likely that the same impacts would be noted. Of the 24 third harvests in the statewide monitoring trials (eight irrigated sites x three years), 12 (six of eight growers) were harvested during the critical late summer period. It is apparent that a significant level of education for growers is needed on this topic. Aside from the severe economic losses in hay production from poorly-timed harvest, these data indicate that harvest management has critical implications on stand longevity and crop rotation. Nitrogen credits from alfalfa stand termination and weed problems should be considered by alfalfa producers in their farming plans for long-term sustainability. D. Insecticide Trials: Mixed results were obtained in the single-application insecticide trials at two locations. In The Amsterdam 1 site, average CRC root feeding damage following Furadan application (ASI = 1.13) was significantly lower than the control (ASI = 1.79, Table 11). At the Amsterdam 2 site, there was no statistical difference in CRC feeding damage between the control (ASI = 1.38) and Furadan-treated (ASI = 1.35) plots (Table 12). In the Amsterdam 2 trial, the average incidence of CRC root feeding damage increased from 10% in the spring to 88% on 3 October 2005 when the trial was terminated. In the same period, CRC adults collected were 0.3 per 10 sweeps and the spring and 11.5 per sweep in the autumn. Based on the rapid CRC symptom development at the Amsterdam 2 site in 2005 and the different results in these two trials, it appears that the timing of insecticide application is critical. Further, the migration of CRC adults after insecticide application from untreated areas (the majority of the field and control plots) and the short duration of Furadan activity may confound the results of these plot trials. Trials of multiple-applications of insecticide were conducted at two locations. In the Huntley trial, the initial Furadan application was sprayed on the Fall and Spring/Fall treatments during the year of establishment. Very few CRC adults were collected throughout the trial (Table 13). The incidence of CRC root damage increased from 7% in May 2004 to 100% in May 2005. All Furadan treatments had lower (P< 0.05) CRC feeding damage severity compared to the control in May 2005, however these differences diminished by September 2005 (Table 13). The severity of CRC feeding damage declined in Spring 2006 (Fig. 11), but this is likely due to variability in scoring technique. In May 2006, CRC root feeding severity in Spring and Spring/Fall insecticide treatments were significantly lower than the control and Fall treatments (Table 13). There were no differences among treatments for stand density or the numbers of other insect pests in this trial (Table 13). The results from the Huntley site suggest that early (year of establishment) and repeated insecticide applications may slow the progression of CRC damage in an infested site. However since the insecticide treatment dates were not continuous across years (Furadan treatments did not occur in Fall 2005), it is unclear if the effect of the effect of the insecticide diminished or there are continual migrations and re-infestations by CRC. In the Bozeman trial, the Furadan treatments were initiated in October 2005 during the planting year, and the insecticide treatments were continuous throughout the trial (Table 14). The incidence of CRC root feeding damage increased rapidly from 5% in May 2006 to 85% in October 2006. The severity of CRC root feeding damage in the control (ASI = 3.00) was significantly higher than all Furadan treatments (ASI mean = 1.90) in May 2007 (Table 14). There were no statistical differences among treatments for stand density or numbers of CRC adults and other insect pests sampled during the trial. Previous literature includes reports of varying effectiveness of insecticide treatments in reducing root feeding damage by CRC. Dickason et al. (1968) found no significant differences in alfalfa yield or plant mortality following insecticide treatments to control CRC. In contrast, Neal and Ratcliffe (1975) reported that one early season application of granular carbofuran (Furadan) reduced CRC larval feeding and resulted in significantly higher levels of regrowth as compared to the control. The results from the Amsterdam 1 and Amsterdam trials had varying results similar to published single-application insecticide trials. Very little research has been published evaluating CRC dynamics over several years with repeated insecticide applications. In the multiple-application trials (Huntley and Bozeman), Furadan treatments were initiated in the year of alfalfa planting. The results from these insecticide trials indicate that alfalfa root damage by the CRC can be delayed but likely not eliminated. Evaluation of these trials over a longer period would be beneficial. While the results from these insecticide trials are promising, much more research is needed in Montana. Fairly low adult CRC numbers were present in sweep samples taken in the spring and fall at the time insecticides were applied. Without a thorough understanding of the CRC life cycle and biology, insecticide application is very haphazard. Specifically, simple enumeration methods for CRC larvae in field soil and models for peak CRC oviposition and larval activity based on heat units or date would be very useful. Data from the insecticide trials indicated that the timing of Furadan application is critical. Likely, in some instances the carbofuran was ingested by larvae which may have reduced immediate feeding damage. However, in all cases the positive effects of insecticide treatments appeared to diminish over time. The efficacy, economics and sustainability of multiple applications of insecticides on alfalfa hay are also in question. Furadan was clearly a useful research tool in this project, however it is highly unlikely that multiple insecticide applications over multiple years of an alfalfa stand would be a desired practice. Literature Cited: Bright, D.E. 1994. Revision of the Genus Sitona (Coleoptera: curculionidae) of North America. Annals Entomol. Soc. Am. 87(3): 277-306. Dintenfass, L.P. and G.C. Brown. 1988. Influence of larval clover root curculio (Coleoptera: Curculeonidae) injury on carbohydrate root reserves and yield of alfalfa. J. Econ. Entomol. 81: 1803-1809. Dixon, P., S.D. Cash, J. Kincheloe and J.P. Tanner. 2005. Establishing a successful alfalfa crop. Mont. St. Univ. Ext. Montguide 200504. http://www.animalrangeextension.montana.edu/articles/forage/alfalfa/alfalfa_est.htm Godfrey, L.D. and K.V. Yeargan. 1989. Effects of clover root curculio, alfalfa weevil (Coleoptera: Curculeonidae), and soil-bourne fungi on alfalfa stand density and longevity in Kentucky. J. Econ. Entomol. 82: 1749-1756. Hower, A.A., M.A. Quinn, S.D. Alexander and K.T. Leath. 1995. Productivity and persistence of alfalfa in response to clover root curculio (Coleoptera: Curculeonidae) injury in Pennsylvania. J. Econ. Entomol. 88: 1433-1440. Kalb, D.W., G.C. Bergstrom and E.J. Shields. 1994. Prevalence, severity, and association of fungal crown and root rots with injury by the clover root curculio in New York alfalfa. Plant Dis. 78: 491-495. Leath, K.T. and A.A. Hower. 1993. Interaction of Fusarium oxysporum f. sp. medicaginis with feeding activity of clover root curculio larvae in alfalfa. Plant Dis. 77: 799-802. Neal, J.W. Jr. and R.H. Ratcliffe. 1975. Clover root curculio: control with granular carbofuran as measured by alfalfa regrowth, yield, and root damage. J. Econ. Entomol. 68: 829-831. Pacchioli, M.A. and A.A.Hower. 2004. Soil and moisture effects on the dynamics of early instar clover root curculio (Coleoptera: Curculionidae) and biomass of alfalfa root nodules. Environ. Entomol. 33: 119-127. Phillips, W.G. and L.P. Ditman. 1962. Studies on biology and economic importance of the clover root curculio Sitona hispidulus (Fab.) in Maryland. MD Agric. Exp. Stn. Bull. A-121. 21 pp. Tan, Y. and A.A. Hower. 1991. Development and feeding behavior of clover root curculio (Coleoptera: Curculeonidae) larvae on alfalfa. Environ. Entomol. 20: 1013-1018. Undersander, D., C. Grau, D. Cosgrove, J. Doll and N. Martin. 1998. Alfalfa stand assessment: is this stand good enough to keep? University of Wisconsin-Extension, Cooperative Extension. Publication#A3620. Wunsch, M.J. and G.C. Bergstrom. 2006. Brown root rot of alfalfa caused by the fungal pathogen Phoma sclerotioides. Report of survey results. Dept. Plant Pathology, Cornell University, Ithaca, NY.
All activities in this project targeted optimal stand longevity of alfalfa in hay production systems. A prime result of this project was the demonstration of the widespread distribution of CRC in Montana. This pest has frequently been detected at numerous locations, and in this project the feeding damage by CRC was monitored in multiyear sites across diverse locations and grower practices. Previous literature suggests that feeding damage by CRC is directly related to increased incidence and severity of root and crown pathogens. Our results indicate that this relationship is predominantly temporal. Damage by CRC feeding, crown rot and root rot progress over years in an alfalfa stand, but correlations among CRC and root or crown rot symptoms of individual plants are very low.
In insecticide trials, we found that multiple applications of Furadan delayed the progression of CRC damage, but did not eliminate it. While useful for research purposes, multiple applications of insecticides over several years of an alfalfa stand is likely cost-prohibitive and unsustainable. More research is needed to determine the peak activities during the CRC life cycle to target specific control measures.
Statewide monitoring of 12 Montana alfalfa stands over three growing seasons for the prevalence of pests, stand mortality and grower practices was very instructive. In addition to CRC, crown rot and root rot symptoms, we demonstrated that alfalfa mosaic virus (AMV) is widely prevalent in the state, infecting 56% and 10% of plants in dryland and irrigated sites in the third year, respectively. Use of the DAS-ELISA procedure enabled accurate diagnosis of AMV, because visual AMV detection is unreliable. The absence of the causal organism for brown root rot in the 12 sites is a very promising result. Currently, no cultivars with resistance to this pathogen are available. The only other cultural control measure for this pathogen is a crop rotation out of alfalfa for four or more years, which could be very disruptive for livestock producers who rely on stable acreages of alfalfa hay.
Additionally in the 12 statewide monitoring trials, we encountered producer practices that are uneconomical or directly impact alfalfa stand longevity. The awareness of the losses caused to first-cut alfalfa hay due to alfalfa weevil larvae has increased greatly since the 1990’s. Four growers in the statewide trial applied nine insecticide treatments to control alfalfa weevil larvae (AWL) prior to first harvest, despite only one site having counts that were above our current recommended threshold. Many growers recognized that “early harvest” (MAES recommendation) is a good strategy to avoid AWL losses, and this will be a topic of future Extension presentations. A second practice relates to the timing of late summer harvests to allow for optimal overwintering by alfalfa. In numerous trials, we have demonstrated that harvesting irrigated alfalfa in early September reduces yield and stand longevity. In the statewide trial, 12 of 24 third-harvests at irrigated sites were taken during this interval. The risks to stand persistence by this practice will continue to be an important topic at upcoming Extension workshops and field days.
In the future, there are several anticipated outcomes from this project. It is likely that more intensive investigations on the CRC will be initiated. In the cultivar evaluation trials, there were no differences among alfalfa varieties for tolerance to CRC feeding damage, however there was a low frequency of plants with limited feeding damage that were selected. If this is a heritable trait, it may be possible to develop cultivars which are more tolerant or inhibit feeding by CRC. There is a significant level of crown and root disease in Montana alfalfa varieties that have high levels of multiple pest resistance. After proper identification of the organisms isolated from diseased plants in the statewide trial, direct selection for resistance to those pathogens could commence. Other practices such as grass-alfalfa mixtures appear to have many advantages for livestock producers, and the information gained from this project will be applicable for making future recommendations.
Educational & Outreach Activities
Numerous publications have been initiated during the initiation and progression of this project. One abstract and a reviewed fact sheet have been written:
Baril, R., C. Tharp, S. Blodgett, K. Kephart and D. Wichman. 2005. Taproot damage by clover root curculio, Sitona hispidulus (Coleoptera: Curculionidae) and other factors affecting alfalfa stand longevity in Montana. Abstr. Entomol. Soc. Amer. 15 -18 Dec. Fort Lauderdale, FL.
Cash, S. D. R.L. Ditterline and M. Manouikian. 2008. Proper late summer harvest management of alfalfa. http://www.animalrangeextension.montana.edu/articles/forage/hay/alfalfaharvest.htm
Two manuscripts are in preparation for submission to refereed journals. These include a summary of the harvest management trials and results from the statewide pest monitoring survey. A third planned manuscript will be a summary of the insecticide trials.
The preliminary data from this project have been incorporated into Extension and outreach presentations. In 2006 and 2007, this information was presented at 8 workshops to 120 crop advisors or agency personnel, and in 20 field days or informal meetings to 766 agricultural producers. A mid-term survey was completed by the 12 cooperators in the statewide pest monitoring trial in January 2007 (Appendix 1). These survey results provided an improved context for the preparation of this final report and future newsletter articles and workshops.
A major output of this project was a fairly detailed final summary of results provided to all 12 producer cooperators and county agents at the termination of the trial (Appendix 3). Initial feedback from both agents and producers has resulted in numerous requests for future field days and workshops.
At the conclusion of this project, simple economic evaluations were computed for several important findings.
A. Costs of unnecessary insecticide applications: three producers at irrigated sites applied eight insecticide treatments to control AWL infestations prior to first harvest. Of these eight treatments, the growers had intended to harvest early rather than spray insecticide on two sites, so the costs of unnecessary insecticide was evaluated for six cuttings. Costs for insecticides and applications costs ($18.00 to $21.50 per acre) and values for hay in 2005 through 2007 ($70 to $95 per ton) were used to develop estimated gross returns. The costs of the unnecessary applications insecticide ranged from $21.50 to $60.00 per acre (Table 15). At high production levels, these additional costs only accounted for losses in gross revenue of 1.6 to 3.9%. From a risk management standpoint, these producers recognize that insecticide treatments can be economically used to prevent severe AWL losses. However, better insect monitoring should be practiced to eliminate unnecessary costs and detrimental impacts on beneficial arthropods.
B. Poorly-timed harvests in late summer can have a major impact on alfalfa stand persistence. For commercial hay producers with short crop rotations, this principle can be ignored. However, most producers who desire long-term stands are reluctant to leave a vigorous crop standing in the field in early September. Another complication is the widespread use of aftermath forage growth in alfalfa fields for grazing in late fall and winter. From past trials conducted on alfalfa in three-cut systems, we have noted that annual yield is very similar regardless of when the third harvest occurs.
Two simulated rotations were developed for irrigated conditions from data from this project and previous trials. In the first rotation, alfalfa is harvested for hay in a three-cut system ignoring the date of the third harvest (Table 16). It is assumed that the alfalfa stand will require rotation after six years of production, with two years of crop rotation prior to re-establishing alfalfa. In the second management regime, alfalfa is harvested twice prior to early August, and the aftermath is grazed (or ensiled). These stands will be renovated after eight years, with two years of an alternate crop prior to replanting alfalfa.
After 25 years in this simulation, there are distinct differences in the management regimes. In the first system, the field has begun its fourth rotation cycle compared to the hay-aftermath system still in its third rotation cycle (Table 16). There is a slight economic advantage for the hay-stockpile system ($961.50 per acre over 25 years). However for many livestock producers, the major benefits would be reduced workloads, lower risks associated with tillage and farming practices, and the significant level of high quality forage for aftermath grazing. This simulation needs to be verified in the field, but is a realistic systematic approach for alfalfa stand management in Montana.
C. Nitrogen Credits from alfalfa: One interesting sidelight from this WSARE project was an accurate estimation of the N credits available from a terminated alfalfa stand. Random root/crown samples excavated from the cultivar trials (Table 10) were analyzed for total N concentration (mean = 2.8%). Based on the biomass of roots and crowns remaining after terminating alfalfa in its fourth year, potential N credits ranged from 123 to 208 pounds per acre. At present N prices, these are equivalent to $74 to $125 per acre.
The final summarization of the data in this project has only recently been completed. Twelve producers in the statewide monitoring trial have an aggregate of 5721 acres of alfalfa. The sites and management practices appear to be representative of much of Montana’s 1.5 million acres of alfalfa grown for hay. Preliminary results from the trials have been presented to 886 producers, agri-business clients and other agencies. A significant impact of the project was a result of the bimonthly sweep sampling and monitoring for insects by county agents and producers. Most of the 12 producers are very keen to employ their new knowledge of insect thresholds (particularly alfalfa weevil larvae) to judiciously make decisions about insecticide applications. Aside from economic considerations, unnecessary insecticide applications increase exposure and are inconvenient for many integrated crop-livestock enterprises.
Workshops on alfalfa stand have been well received. To date, there is much skepticism among hay producers on the topic of alfalfa harvest schedules. In recent workshops, a systems approach to alfalfa for either commercial hay production or long-term hay-stockpile management has generated a great amount of interest.
Areas needing additional study
Several research topics requiring additional investigation were generated from this project. The 12-location monitoring trial provided a significant amount of information on alfalfa for three years of production. At the completion of this project, we identified many factors related to stand persistence, however the measurements did not reach the end point of stands requiring renovation. Sustainable alfalfa stands might be developed through management practices to persist over 10 years on irrigated land or 20 years on dryland. Unfortunately, no funding sources are available for this type of research.
Additional crop breeding efforts should be aimed at improving alfalfa persistence per se, and resistance or tolerance to crown rot, root rot, clover root curculio (CRC) larvae feeding damage and other pests. It appears that there is adequate variability in alfalfa populations to improve these traits. Genetic improvement in alfalfa is generally superior to other means of pest control, and it would complement other methods in an integrated program. Brown root rot should continue to be monitored in Montana. Despite its absence in this study, it has been confirmed in several counties.
More research trials should be conducted to determine the impacts of nurse crops on alfalfa establishment and persistence, particularly on dryland. Better techniques for enumeration and predicting peak CRC activities are needed. The damage from this pest appears to be responsive to insecticide treatments, however more targeted control methods would be beneficial.
During this project, we noted that many crop consultants, county agents and producers need an elevated level of training and experience with alfalfa production and management practices, diseases and insect pests. Alfalfa IPM is a recognized model program in the U.S., but there ia often a disconnect in relating alfalfa management to pest management in the field.