In Gainesville summer fallow tillage and infrared transmitting (IRT) film used in combination with a vigorous crop can effectively suppress purple nutsedge infested areas for organic production. In Tifton, yellow nutsedge and other weeds were suppressed by IRT film but propane flaming, sunn hemp cover crop, and fallow-tillage the preceding summer were not effective. Yellow nutsedge was absent from fall-seeded crops in both years, regardless of the preceding summer treatment, suggesting that the timing of cultural practices may be a useful means to avoid losses from yellow nutsedge. At Clemson, frequent tillage or use of IRT film with or without turnip followed by handweeding was not effective in eradicating purple nutsedge. Season-long management was essential to prevent increases in purple nutsedge tuber density over time.
The overall objective of this project is to evaluate weed management strategies for use in the integrated management of purple nutsedge and yellow nutsedge in organic vegetable production systems for the southeastern US.
1. To compare of the summer fallow techniques of a summer cover crop, soil solarization, clean fallow with disking, clean fallow with flaming, and a weedy fallow on purple nutsedge population density, tuber number and size distribution, and tuber viability.
2. To evaluate the persistence of suppression in two subsequent fall cash crops with differing canopy sizes and rates of growth and development.
3. To compare the effect of clean fallow and an allelopathic winter cover crop on purple nutsedge tuber viability.
4. To assess the effect of spring crops of differing canopy type and rate of growth and development and weed-suppressive synthetic mulch (IRT – infrared transmitting film).
5. To identify a combination of treatments applied in sequence that result in the most cost effective and efficacious suppression of purple nutsedge.
1. To compare of the summer fallow techniques of a summer cover crop, soil solarization, clean fallow with disking, clean fallow with flaming, and a weedy fallow on yellow nutsedge population density, tuber number and size distribution, and tuber viability.
2. To evaluate the persistence of suppression in two subsequent fall cash crops with differing canopy sizes and rates of growth and development.
3. To compare the effect of clean fallow and an allelopathic winter cover crop on yellow nutsedge tuber viability.
4. To assess the effect of spring crops of differing canopy type and rate of growth and development and weed-suppressive synthetic mulch (IRT – infrared transmitting film).
5. To identify a combination of treatments applied in sequence that result in the most cost effective and efficacious suppression of yellow nutsedge.
Clemson, South Carolina
1. To evaluate purple nutsedge tuber dynamics over two growing seasons using various integrated strategies in organically grown fall-planted bell pepper.
2. To compare the economics of various integrated strategies for purple nutsedge management.
Gainesville Economic Analysis
To compare the monetary costs and returns to producers in comparisons to conventional (non-organic) production systems, non-market environmental and social benefits associated with reduced consumption of pesticides, and regional economic impacts of expanded local vegetable production.
The purpose of this project is to develop an effective holistic management system for controlling purple and yellow nutsedge in organic vegetable production systems. Infestations of perennial weeds are significant obstacles to organic production and can result in growers removing infested acreage from production. A systems approach to perennial weed suppression for organic farms in the southeastern US with purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus) infestations is outlined. The relative effectiveness of individual control measures also will be evaluated by nesting such practices within the systems under evaluation (Drinkwater, 2002). The primary focus of the study addresses the second priority area for 2005 funding in that the intended outcome is the development an integrated management strategy for improving weed management that is compatible with organic vegetable production enterprises of all sizes. The multistate study involves a systems approach and will be conducted on-farm at Rosie’s Organic Farm in Gainesville, Florida, and at research farms at Tifton, Georgia, and Clemson, South Carolina. We are interested in systems that not only promote biodiversity and that are protective of the environment, but that are cost-effective for the farmer and accrue economic benefits.
Conventional weed management is strongly dependent on herbicide use and as a result a large proportion of research time and effort has focused on chemical control of weeds. Due to the high cost of herbicides, limited availability of herbicides for minor crops, and increased environmental concerns, researcher interest in issues of sustainability and integrated weed management has intensified. Although weed management has been identified by organic producers as a major constraint to organic production, and was established as their number one research priority (Walz, 1999), research in the area of organic weed management has received much less attention.
In a recent review of studies of weed management in organic farming, it was noted that most of the studies used the reductionist approach that is typical of studies done for conventional production (Bàrberi, 2002). The need for a more holistic or system approach to pest management is being advocated both by scientists (Bàrberi, 2002; Lewis et al.; 1997) and organic growers (workshop sponsored by the Florida Certified Organic Growers and Consumers, Inc. (FOG) in November 2001), and the Organic Farming Research Foundation (OFRF) (Lipson, 1997). More importantly the National Organic Standards require that producers use a planned systems approach to weed management. The approach encourages practices that improve soil health, promote good sanitation measures, and employs cultural practices that enhance crop diversity, the utilization of crop varieties that are more competitive against weeds, and the control of weeds and other pests through mechanical, physical, and cultural methods. Non-synthetic biological, botanical, or mineral inputs may be employed to manage weeds; however, these substances are allowed only when the practices described above are insufficient to prevent or control them. If such a substance is necessary for weed control, then a biological or botanical substance or a substance included on the National List of allowed synthetic substances is acceptable for use in crop production (Koenig and Baker, 2002). Currently, a very limited number of organic herbicides are available for organic producers and none of these materials can sufficiently control purple and yellow nutsedges.
Nutsedges are perennial, herbaceous plants that propagate primarily by underground tubers. Not only are they a significant problem in the Southern region, they are regarded among the world’s worst weeds due to the wide range of crops infested in many countries (Holm et al., 1977). Purple nutsedge tubers typically occur in chains. Apical dominance within a tuber chain restricts sprouting to the most apical tuber and sprouting of other tubers is inhibited. Yellow nutsedge is a closely related species. It differs from purple nutsedge in that tuber chains are not produced. Each tuber is borne singly at the end of a rhizome. Unlike purple nutsedge which has a range in the southeast US from Florida to Virginia and west to Texas, yellow nutsedge is adapted to cooler environmental conditions and is found in all states of the continental US (SWSS 1998.). Nutsedge infestations cause serious problems in various horticultural and agronomic crops. Purple nutsedge is among the ten most common and/or troublesome weeds in many crops throughout the southern United States (Bryson, 1989; Dowler, 1993).
In addition to dormancy, nutsedge tubers can also exhibit quiescence during conditions that are unfavorable for sprouting. Both species can negatively affect crop growth and yield through competition for resources (Morales-Payan et al, 2003) and purple nutsedge also causes allelopathic interference; Quayyum et al., 2000). We have found evidence at Rosie’s Organic Farm that purple nutsedge can serve as an alternative host for rootnot nematode (Meloidogyne incognita) (Myers et al., 2004). However, at a second organic location (Hammock Hollow Farm), which utilizes cover crops during the summer fallow period to a greater degree than Rosie’s, infestation by plant pathogenic nematodes was much lower. In recent studies we have evaluated the leguminous cover crops sunn hemp (Crotalaria juncea), velvetbean (Mucuna deeringiana), and cowpea (Vigna unguicuata cv. Iron Clay) to identify optimum plant populations for the suppression of weed growth during fallow periods (Collins et al. 2003).
The management of nutsedges on organic farms is critical since low uncontrolled populations lead to accumulation of tubers and worsening of the infestation. In another study at Rosie’s Organic Farm, high, uncontrolled populations of purple nutsedge resulted in complete crop loss (Warnick et al., 2006). Efforts to control nutsedges through non-chemical means are not new. Some of the results of earlier control and eradication studies are still pertinent (Davis and Hawkins, 1943; Day and Russell, 1955). Tillage operations to unearth purple nutsedge tubers can be effective since the tubers rapidly lose viability when dried. Yellow nutsedge tubers appear to be less susceptible to desiccation than purple and, therefore, tillage to achieve control of these species by desiccation is likely to work only with purple nutsedge (Day and Russell, 1955). A more likely method of controlling both species is by depletion of tuber reserves. Davis and Hawkins (1943) reported that nutsedges can be controlled by means of weekly removal of shoots under moist soil conditions that promote resprouting. Depletion of smaller tubers through multiple shoot removal operations is also supported by the work of Santos et al. (1997a).
Many non-chemical methods such as solarization, suppression with translucent mulches, tuber depletion, plant residues, cover cropping, crop rotations and tillage to expose tubers to adverse environmental conditions have been employed individually for the management of purple nutsedge with varying degrees of success (Chase et al., 1999ab; Chivinge, 1992; Long, 1988; Norsworthy, 2003; Patterson, 1998, Smiley, 2002). In addition to the Long, Norsworthy, and Smiley SARE reports, two other SARE projects have reported on the efficacy of various non-chemical approaches to dealing with nutsedge infestations (Coates, 1996; Kloepper, 2003; Long, 1988; Norsworthy 2003; and Smiley, 2002). Coates (1996) found that although their mechanical digger would remove nutsedge tubers from soil to 6 inch depth, it was not commercially viable since nutsedge shoots emerged from tubers deeper in the soil that tilling deeper than 6 inches was not energy efficient. Kloepper (2003) found that clover and oat winter cover crops failed to suppress yellow nutsedge.
The energy of the sun can be utilized to disinfest moist soil by covering the soil with clear polyethylene film during the hottest months of the year. This process is termed soil solarization. Some clear thermal-infrared absorbing films are formulated with constituents that result in higher soil temperatures than standard low density polyethylene (Chase et al., 1999a). Such temperature enhancement can be a benefit since the weather during the hottest months of the year in Florida can be overcast and rainy, which limits the effective of soil solarization.
The mechanisms of suppression of nutsedges (C. rotundus and C. esculentus) by soil solarization and by infrared transmitting (IRT) film are related. We have found that although nutsedges readily penetrate opaque polyethylene films, they are less able to penetrate transparent films. Patterson (1998) also reported little penetration of translucent IRT films. Light penetrating clear and IRT mulches causes a change in growth from rhizome elongation to leaf expansion, and nutsedge plants become trapped under the mulch (Chase et al. 1998). With clear mulches this can result in foliar scorching and tuber depletion and with IRT film only very low levels of photosynthetically active radiation penetrate the mulch, sufficient to induce photomorphogenesis, but insufficient to promote nutsedge growth and tuber formation. These data with IRT film are supported by the finding of Santos et al. (1997b) that a linear decline in shoot and tuber dry biomass occurs with increase in shade such that no tubers were produced with shade in excess of 70 percent.
Foliar scorching is an important mechanism of for nutsedge control with soil solarization since many tubers occur at soil depths that do not achieve temperatures that are lethal to nutsedge tubers. When Chase et al. (1999b) exposed purple nutsedge tubers to diurnally fluctuating temperatures that are typical with soil solarization, they found that temperature regimes with a maximum temperature of 45C just slowed the emergence of nutsedge shoots. However, regimes with a temperature maximum of 50C were lethal to nutsedge tubers.
Flame weeding or flaming has been shown to be an effective method of weed control that is dependent on weed size, leaf thickness, and whether the weeds possess protected growing points (Ascard, 1995). Flaming controls or suppresses weeds by removing part of or the entire shoot, killing or slowing the development of weeds. Perennial weeds often readily regrow after such treatment. A similar response could be expected from flaming of purple nutsedge, which will kill the shoots but will not control tubers. Therefore, flaming will provide only temporary suppression unless combined with other methods of control or done multiple times during the fallow period in order to exhaust tuber reserves through multiple sprouting and shoot removal events. Santos et al. (1997a) have evaluated the potential of tubers of various sizes to resprout after their shoots have been removed by clipping every 6 days for a maximum of seven removals. When the initial clipping was done 6 days and 12 days after sprouting tubers, it was possible to deplete 0.25 g purple nutsedge tubers after 5 and 6 clippings, respectively. However, 0.5 g tubers required 6 shoot removals before tuber depletion occurred when clipping was initiated 6 days after sprouting. Larger tubers of 0.75 and 1 g and 0.5 g tubers with the first clipping occurring 12 days after sprouting were not depleted.
Leguminous crops, including cover crops, can be particularly valuable components of organic farming rotations. Organic producers commonly utilize crop rotations and cover crops in their cropping systems and they have identified them as important research priorities (Waltz, 1999). In the survey, researchers found that crop rotation was a recurring pest management strategy used by farmers. Rotations were used for insect pest management (75% of respondents), disease and nematode management (80% of respondents), and weed control (75% of respondents). Crop rotation and cover crops are important components of organic systems because they contribute to healthy soils, biodiversity of the system, and suppression of pests.
Leguminous cash crops and cover crops fix nitrogen and thereby can be used to improve soil fertility directly by addition of nutrients and contribute indirectly by addition of soil organic matter, which improves nutrient holding capacity. Some legumes also demonstrate allelopathic potential, suppressing pathogenic nematodes and/or weeds.
None of the treatments described above are individually capable of effectively managing nutsedges sustainably and economically. Therefore, we propose that integration of several of these strategies into a systems approach to vegetable crop management may provide improved weed suppression and crop yields.
Economic Analysis of Integrated Weed Control in Organic Vegetable Production
Organic fruit and vegetable production in the United States has grown significantly in recent years, as consumers have become more aware of the freshness and potential health benefits of organic foods. The top organic fresh fruits and vegetables purchased in the U.S. are tomatoes, leafy vegetables, carrots, apples, potatoes, peaches, bananas and squash. Sales of organic produce were estimated at $10.4 billion in 2003, or about 1.8 percent of total U.S. retail food sales. Growth through 2010 is forecast at 9 to 16 percent annually, with sales projected to reach $23.8 billion or 3.5 percent of total retail food sales (Oberholtzer, Dimitri and Greene, 2005). Growth in the industry has been stimulated by the Organic Foods Production Act (1990) finally instituted in 2002 to provide standards for organic food production.
During the 2000-05 period, certified organic vegetable production area in the U.S. increased from 62,342 to 98,525 acres, while in twelve southern states production area grew from 4,213 to 9,048 acres (Table 1). Significantly higher prices received for organic produce, and development of high-value niche markets have encouraged more growers to adopt organic practices. The leading states in the region for organic acreage are Florida and Virginia. However, organic production in the southern U.S. has not been adopted as rapidly as some other areas due to intense pest pressures, and perceived lack of control by producers, and organically managed production remains small in comparison to overall production.
This project sought to evaluate the costs and returns to organic vegetable production systems in comparison to conventional (non-organic) production, through cost accounting and analysis of wholesale markets. Specifically, the economic outcomes of organic weed control practices were evaluated, including organic and plastic film mulches, cover crops with mulching or disking, soil solarization, flaming and tillage. Four crops were selected for study in this research: broccoli, leaf lettuce, bell peppers and squash. Production area, harvested area, production volumes, average yields, prices and values for these crops in the U.S. in 2007 are summarized in Table 2. Broccoli is the largest crop at 736,849 acres, followed by leaf lettuce (656,355 acres), bell peppers (468,387 acres) and squash (227,518 acres). There is significant production of bell peppers and squash in Florida, Georgia and South Carolina.
Price premiums for organic versus conventional produce have been examined for several important vegetable crops, including broccoli, carrots and mesclun mix (Kremen, Greene and Hanson; Oberholtzer, Dimitri and Greene, 2005), using a database of organic prices available at www.ers.usda.gov/tata/organicprices. Weekly farmgate prices (f.o.b. shipping point) for organic and conventional broccoli during 1999-2007 are shown in Figure 1. It is apparent that prices may vary dramatically, and are especially volatile for organic broccoli, but prices for both products typically move together, and the organic price premium has slightly increased over time. The overall average price for organic broccoli was significantly higher than the conventional broccoli ($16.14 vs. $7.16 per carton, 14-18 bunch count), representing a 2.25 fold price premium. Organic price premiums for carrots were of similar magnitude. Generally, the organic premium is greater at the wholesale market level than at the farmgate level.
Locations and Species
Field experiments are proposed with a systems approach to management of purple and yellow nutsedges in the southeastern US where both species of nutsedges are problems. Researchers will pool their knowledge and experience to allow evaluation of efficacy and cost effectiveness of a wide range of control techniques to be utilized concurrently or in succession for the integrated management of both species. The occurrence of the two nutsedge species throughout the southeast, the differences in climate from Florida to South Carolina and the economic importance of different crops in the different regions have led to adaptation of the experiments to locations, so that the three proposed studies are not identical. It affords us an opportunity to collaborate on a common problem and broadens the scope of the work and inferences that can be drawn.
In Gainesville, the project will be conducted on certified land on Dr. Koenig’s organic farm (Rosie’s Organic Farm, Gainesville, FL) where there is already a heavy purple nutsedge infestation. The other studies will be conducted on research station farms on non-certified land. Only two states in the southeast have certified organic acreage (Sooby, 2003) and prior to obtaining certified research acreage, North Carolina State University demonstrated that research applicable to organic systems can be accomplished on noncertified land. Dr. Norsworthy has been actively involved in evaluating weed management strategies in organic agriculture over the past few years, with funding through sources such as the OFRF. The farm at Clemson is not certified site because of the difficulty in establishing effective buffers. However, crops are produced using certified organic practices. Considerations in the data analysis may need to be made based on these site specific constraints.
Although the best situation would be on-farm evaluation, to achieve the level of infestation needed in a sufficiently large area to conduct the study would require deliberate infestation of organic growers’ fields. Nutsedge species are recalcitrant even in conventional systems and we prefer not to increase existing infestation on grower acreage to facilitate the research. Efficacious and cost effective management systems that arise from this project can be validated on certified grower acreage in future projects.
In early June 2005 the weed population at the experimental site will be evaluated. Weed species will be identified and counted to define the species present and to estimate the shoot and tuber populations prior to establishment of the weed management systems. Six systems will be initiated in a randomized complete block design with four replications in 0.25 acre field infested with purple nutsedge. Plots 12 ft wide and 40 ft long will be established. Quadrats (0.25 m2) will be randomly placed within each plot to assess initial purple nutsedge shoot densities. Multiple soil samples will be taken from each main plot to a depth of 10 inches using a golf cup cutter to determine the initial tuber density, tuber size distribution, and tuber viability. To test tuber viability, tubers will be cut in half. One half will be incubated for 30 minutes in 0.1% triphenyl tetrazolium chloride solution while the other half is held in water. The development of a pink color in previously white tubers will indicate viability.
Objective 1: To compare of the summer fallow techniques of a summer cover crop, soil solarization, clean fallow with disking, clean fallow with flaming, and a weedy fallow on purple nutsedge population density, tuber number and size distribution, and tuber viability.
Summer fallow treatments will be initiated in mid-June, 2005. All plots except for the weedy fallow will be tilled to provide a friable, weed free, surface. A legume cover crop (Crotalaria juncea – sunn hemp) will be used in two of the systems. In System 1, the cover crop residue will be retained on the soil surface as organic mulch for the fall cash crop, and in System 2 it will be incorporated to provide a nutrient source. The nutrient source for all other systems will be composted manure. System 3 will be initiated with soil solarization, System 4 will have a clean fallow with tillage, a clean fallow in System 5 will be maintained by flame weeding, and in System 6 the existing weed species will be retained for a weedy fallow. The clean fallows will be flamed weeded or rototilled weekly and irrigated monthly to stimulate sprouting and depletion of tubers. Although this is hard on the soil, it may be necessary to achieve tuber depletion and to reduce the number of viable purple nutsedge tubers by desiccation in the case of the tillage. Fallow treatments will be conducted until the end of August when the nutsedge tuber populations and tuber viability will be reassessed.
Soil solarization will be conducted by mulching preirrigated soil with clear solarization polyethylene film. Soil temperature in the solarized treatment will be measured at 30-minute intervals at 5 and 10 cm depths using a CR10 datalogger equipped with copper-constantan thermocouples. The temperature of non-solarized beds will also be measured for comparison. At the end of August, the solarization film will be removed, and the cover crop will be sampled for biomass accumulation and undercut or incorporated, and the weedy fallow plots tilled in preparation for cash crop establishment. Sunn hemp for incorporation will be undercut and incorporated by mid-August so that nutrients would be readily available when the fall cash crops are established in September.
Objective 2: To evaluate the persistence of suppression in two subsequent fall cash crops with differing canopy sizes and rates of growth and development.
In September, 6 ft by 40 ft subplots will be marked and broccoli and lettuce will be established from transplants, one species per subplot. These crops and the pepper and squash for spring were selected for their differing rates of growth and canopy structure and are expected to differ in their competitive interaction with purple nutsedge. Nutsedge counts will be taken at 2-wk intervals. After each nutsedge count, the crops will be handweeded and the time needed to hand-weed each treatment will be noted. The broccoli and lettuce will be harvested and marketable yields determined.
Objective 3: To compare the effect of clean fallow and an allelopathic winter cover crop on purple nutsedge tuber viability.
In December after harvest of the fall cash crops, the plots will be tilled to incorporate crop residues and the winter fallow treatments will be initiated. A winter cover crop, rye, will be compared with clean fallow with tillage that will expose nutsedge tubers to desiccation and freezing until the end of February. Broccoli and lettuce plots will be divided into two halves. The rye and clean fallow plots will be established at right angles to the former crops so that half of each broccoli plot and half of each lettuce plot will receive the rye and the other halves of the plots will be rototilled. This would result in winter fallow treatments being applied to 12 ft by 20 ft plots. Data to be collected during winter fallow includes: identification and enumeration of weed species that occur in the rye cover crop treatment; cover crop and weed biomass in rye plots; and nutsedge counts, tuber number and tuber viability in both rye and clean fallow treatments.
Objective 4: To assess the effect of spring crops of differing canopy type and rate of growth and development and weed-suppressive synthetic mulch (IRT – infrared transmitting film).
In early March, the rye will be mowed and retained on the soil surface as an allelopathic organic mulch for weed suppression. Two 6 ft by 20 ft plots will be established and the spring cash crops of pepper and squash randomly allocated to the plots. The clean fallow will be similarly split into two plots, mulched with a weed-suppressive synthetic mulch (IRT) and pepper and squash randomly allocated to the plots. Soil temperature will be measured as described previously, since IRT mulch can be expected to result in warmer soil temperatures than rye mulch. Data will be collected on weed suppression and crop growth and yield. Nutsedge (and other weeds occurring in the rye-mulched plots) will be counted at two week intervals prior to hand weeding plots. Time needed for handweeding will be documented. Crop growth will be evaluated by measuring crop height during the season and sampling plants to obtain dry biomass during and at the end of the season. Fruit will be harvested as recommended by the grower and marketable yield will be determined.
Objective 5: To identify a combination of treatments applied in sequence that result in the most cost effective and efficacious suppression of purple nutsedge.
The experiments described for objectives 1 through 4 will be repeated in the second year and efficacy of nutsedge control for individual seasonal treatments will be established. In addition, the cumulative efficacy of all the treatments applied as a system will also be evaluated (objective 5). Effectiveness will be based on nutsedge control and crop yields achieved. The cost effectiveness of each system will be determined as described below in the section on economic analysis.
The nesting of individual treatments in systems will allow an understanding of which individual treatments and which systems were best and permit prediction of how untested combinations may work to suppress nutsedge populations. A statistician was consulted in the development of the design and will assist in the analysis of the data.
Data involving counts often require the use of transformation for stabilization of variance. Square root transformation will be done on the data prior to analysis if needed. Analysis of variance will be performed using the MIXED procedure of SAS (SAS System for Windows, Version 9). This procedure will accommodate the split plot analyses necessary for analyzing individual studies nested within systems. When significant differences due to treatments are detected with PROC MIXED, treatment means separation will be accomplished using the least squares means option and contrasts.
A study similar to that described above for Gainesville will be conducted by Dr. W. Carroll Johnson at the Coastal Plain Experiment Station Ponder Farm, near Tifton, GA. The primary nutsedge species there is yellow nutsedge and so a field infested with yellow nutsedge will be utilized. Many growers have both nutsedge species to contend with in the southeastern region and assessing both species broadens the scope and impact of the project. Other differences in the procedure at Tifton include the use of direct-seeded turnip green instead of lettuce, since lettuce is not commonly grown in the Tifton area. Cabbage will be substituted for broccoli since it is the more important of the two crops in the Tifton area.
The biology of yellow nutsedge is sufficiently different from purple nutsedge that the outcomes of the Gainesville and Tifton studies may be quite different. Although, tuber depletion is expected to work well on both nutsedge species, yellow nutsedge tends to be taller than purple nutsedge and is less susceptible to competition for light and purple nutsedge tubers are more sensitive to desiccation and freezing than yellow nutsedge tubers. Because of the differences in the studies, data will not be compared across locations. Statistical and economic analyses will be conducted as described for Gainesville.
Clemson, South Carolina
Dr. Jason Norsworthy was responsible for the two-year study conducted at Clemson, SC.
A field experiment was initiated at Clemson, SC, in mid-March 2005 and continued through November 2006. The experimental site had a natural population of purple nutsedge at the initiation of experiment in March 2005. The experiment was organized in a split-plot design with four replications. Main plots consisted of integrated purple nutsedge management strategies from mid-March through July of 2005 and 2006. The main-plot factors were: 1) green polyethylene film, 2) clear polyethylene film, 3) turnip followed by (fb) green polyethylene film, 4) turnip fb clear polyethylene film, 5) tillage every three wks, and 6) fallow. The embossed green film and the smooth clear film were 1.0-mil thick (0.0254 mm). ‘Seventop’ turnip was drill-seeded in 18-cm-wide rows at 6 kg ha-1 in mid-March and flail mowed in mid-June. Immediately after mowing, turnip was incorporated into soil to a 10-cm depth and covered with polyethylene film (green or clear film) through July. The fallow treatment included no nutsedge management, except one tillage in mid-March.
In early-August each year, the main-plot treatments were terminated, and each main plot was divided into three subplots after roto-tilling. Subplots consisted of three factors: 1) handweeding, 2) mulching with wheat straw, and 3) no weeding in bell pepper. Subplots were handweeded once per week in 2005 and once every other week in 2006.
‘Heritage’ bell pepper transplants (4- to 6-leaf stage) were planted at 0.3- by 0.3-m spacing in a double row pattern, a total of 16 transplants per subplot. A 7-cm-thick wheat straw mulch was applied in mulched subplots at 7300 kg per field ha. Plots were fertilized with fish meal (45 kg N, 28 kg P, and 28 kg K ha-1) prior to transplanting bell pepper and were drip irrigated throughout the growing season. Plots were handweeded and straw mulched in a 0.3-m strip adjacent to either side of the planted row (total of 0.9 m wide). The time needed for handweeding bell pepper was recorded for each treatment.
Soil samples (30 samples per main plot and 10 samples per subplot) were pulled to a 15-cm depth using a 7-cm diameter soil probe in early March, early August, and early November of each year. Soil was sieved for purple nutsedge tubers using a 0.5 cm screen and only viable tubers were counted.
Cost of nutsedge management was averaged over both years. The total expenses associated with each integrated strategy included only direct costs, as fixed costs were similar among all treatments. Direct costs included the cost of each input and application cost, excluding cost of fuel, equipment depreciation, and interest on operating capital. Costs were derived from actual expenses incurred and the estimated cost of equipment operation based on enterprise budgets (Ferreira and Rathwell 2006). Polyethylene-mulched treatments included the cost of the polyethylene film, disking, plastic laying, and plastic removal. Treatments combining polyethylene film with turnip included the additional cost of turnip seed, drill seeding, flail mowing, and roto-tilling. Cost of tillage plots included the cost of six roto-tilling operations. The cost of roto-tilling for land preparation in mid-March and early-August were excluded because all treatments were tilled at this time. Handweeding cost was determined by multiplying the number of hours spent hand hoeing by a labor wage of $7 hr-1. Straw mulching cost included the cost of wheat straw and labor wage for applying the mulch.
Data were analyzed using PROC GLM in SAS. Initial tuber population in mid-March, 2005 was used as a covariate factor when analyzing the tuber data. Subplots were compared within main plots for tuber density using Fisher’s protected LSD at a = 0.05 level.
Gainesville Economic Analysis
Pro-forma budget information on costs of conventional vegetable production were compiled for four selected crops: broccoli, squash, green peppers, and lettuce or leafy greens. These budgets were developed by university extension specialists in Florida, Georgia, Alabama and South Carolina (Hewitt, 2006; Smith, 2004; Westbury and Mizelle, 2000; Mizelle and Westbury, 2000), based on consensus opinion of growers, allied suppliers and researchers, and are assumed to represent best management practices. For each budget, information was provided on quantities and prices of inputs used, and total costs per acre. In some cases, separate budgets were available for double cropping practices. Expenses include both direct costs such as seed, fertilizer, chemicals, fuels, equipment repairs, maintenance, cultural and harvest labor, and fixed costs such as rent, asset depreciation and interest. Expense items for each budget were evaluated to determine the items that may change under organic production practices, by substitution of labor and other allowable inputs for non-allowable chemicals and synthetic fertilizers.
For organic vegetable production trials at the University of Florida (2005-07), data were gathered on labor time, direct expenses and vegetable yields by the horticultural investigators in the project. Experimental plots for each crop were 0.132 acres in size. A randomized block design was used to evaluate weed control treatments including SunnHemp cover crops with mulching or disking, soil solarization, flaming and tillage, as well as a weed fallow control. For the spring crops, an infrared reflecting plastic film mulch was also tested in split subplots. Expenses and yields for the small plots were expanded to represent full scale commercial production on a per acre basis. Labor costs were estimated at $8.84 per hour, the average wage for experienced farmworkers in Florida in 2006 (Florida Agency for Workforce Innovation). For comparison to organic production practices, it is appropriate to consider only the preharvest production costs, since harvest/marketing costs and fixed costs can be assumed to be the same for organic and conventional production. Also, fixed costs were not considered since the available budgets were inconsistent in how these were estimated.
Prices for conventional produce were taken from USDA-Agricultural Marketing Service data on farm gate sales and terminal markets. Prices and values for organic products were estimated at 2.25 times the corresponding conventional price.
Soil was sampled for initial purple nutsedge tuber density in late June, 2002 and an initial assessment of existing weed species and nutsedge shoot density was done on July 1. No difference in viable tubers or purple nutsedge shoot density was observed.
Prior to establishing the fall crops, flaming had the highest number of viable tubers of the fallow treatments, with all other treatments similar to the weedy control. However, during lettuce and broccoli crops nutsedge shoot density was suppressed by all fallow treatments to lower levels than with the weedy control, but solarization was the least effective. Leaf-cutting insects eliminated the crops in the sunn hemp mulch treatment within days of being transplanted. Lettuce stands with all other treatments were similar and greater than with the weedy control. Highest broccoli stands were obtained with flaming, solarization, and tillage; but broccoli stand with incorporated sunn hemp was similar to the weedy control. Highest lettuce yields occurred with incorporated sunn hemp, solarization, and weekly tillage. However, lettuce yields with flaming and the weedy control did not differ statistically. Broccoli yields were greatest with flaming, solarization, and tillage. Broccoli development was delayed with the weedy control and incorporated sunn hemp treatments and no significant yield was obtained.
Suppression of nutsedge by summer fallow treatments (2005) persisted into spring 2006, so that in summer squash, all treatments had significantly lower nutsedge infestations than the 219 plants/m2 obtained in the weedy control. Nutsedge densities in fallow treatments ranged from 7 to 51 plants/m2, but were not statistically different. In bell peppers, again, nutsedge density was highest with the weedy control. With the fallow treatments, nutsedge densities were lowest with weekly tillage, intermediate with flaming and sunn hemp-mulched, and highest with sunn hemp-incorporated and soil solarization. In both squash and peppers, the use of IRT film significantly reduced nutsedge infestation. Fallow treatment had no significant effect on zucchini squash yields when grown without IRT film. However, squash yields with all fallow treatments were higher than the control when beds were mulched with IRT film. The use of IRT film significantly increased squash yields by 27% to 48% with the exception of the sunn hemp-incorporated treatment in which the observed was not significant. In the bell pepper crop, fruit yields were highest with weekly tillage and lowest with the weedy control. The use of IRT film increased pepper number by 25% and pepper fresh weight by 21%.
In summer 2006 at the end of the bell pepper harvest but prior to the initiation of the second year of summer fallow treatments, the highest nutsedge plant density was 93 plants/m2. Although this was not significantly different from the 64 plants/m2 with the sunn hemp incorporated treatment, all other fallow treatments had lower levels of infestation than the weedy control (ranging from 54 plants/m2 with solarization to 21 plants/m2 with tillage).
Tuber viability was highest with the weedy fallow in fall just prior to establishing lettuce and broccoli. By Nov. 21 nutsedge plant density in lettuce and broccoli crops were also highest (115 plants/m2) in the weedy control than with all other summer fallow treatments. The lowest nutsedge density was 2.3 plants/m2 and occurred with the tillage fallow treatment. In Fall 2006, lettuce yields were lower with flaming and the sunn hemp incorporated treatments than with the weedy control. All other treatments had yields that were not significantly different from the weedy control. Persistence of control due to winter mechanical fallow and spring IRT film was observed so that lettuce yields were higher in that side of the plots than the side that received winter rye cover crop and no IRT in the spring. This difference was not apparent with broccoli. Lowest broccoli yields occurred with the sunn hemp mulched fallow treatment. Yield with sunn hemp incorporated was intermediate and highest yields were obtained with flaming, solarization and tillage, which were not significantly different from the weedy control. As for fall 2005 plant stand counts of both lettuce and broccoli were negatively impacted by the sunn hemp mulch.
By the end of the spring 2007 season, nutsedge density was highest in the weedy control and significantly lower with all other summer fallow treatments. The use of IRT film resulted in a lower nutsedge density than bare soil. There was no difference in nutsedge tuber viability due to summer fallow treatments or to IRT use. However, there were more viable tubers with the lettuce/pepper system than with the broccoli/squash system. Bell pepper yield response differed depending on whether or not IRT film was used. Without IRT film yields were lowest with weedy and flaming fallow treatments. There was no difference in yield among the sunn hemp treatments, solarization and tillage. However, with IRT film yields with all fallow treatments were not significantly different. Unlike spring 2006, bell pepper yield was improved by IRT film use only where soil solarization was the fallow treatment. In spring 2007 zucchini squash yield was lowest with the weedy fallow treatment. Yield with all other fallow treatments were not significantly different from each other. The use of IRT film resulted in higher yields than zucchini grown on bare ground.
The results indicate that all summer fallow treatments have the potential to suppress purple nutsedge infestations. However, fall leafy vegetable crops were negatively impacted by leaf cutting pests if cover crop residue was maintained as mulch in the fall. Incorporation of the residue may also be problematic either due to allelopathic suppression of seedlings or to nitrogen deficiencies. Because soil solarization is conducted only on the beds reinfestation tended to occur by the following spring, but the use of IRT film helped to ameliorate this problem. Systems that utilized tillage during the summer and IRT film in the spring appear to have the best potential for suppressing nutsedge. The use of vigorous crops such as zucchini squash that grow rapidly and close and form a dense canopy should be used rather than slower developing crops like bell pepper that did not result in a closed canopy.
The results are a further validation that summer solarization has potential as an alternative method of weed management in organic crop production. Propane flaming, fallow tillage, and sun hemp cover crop failed to adequately suppress annual grasses and these weeds increased as the trial progressed and became the yield-limiting factor at the conclusion of the study. In fields with several weed species present, summer solarization was the only treatment that consistently reduced densities of all weed species present.
At the initiation of the experiment in mid-March 2005, average tuber density was 910 tubers m-2 (Figure 2). Purple nutsedge tuber density in fallow plots increased to 1,685 tubers m-2 by August 2005, an 86% increase over the initial density (Table 3). Tuber density in all main-plot treatments was lower than the fallow treatment in August 2005, with the lowest density being in polyethylene film plots. Tuber density was comparable in tillage, turnip fb green film, and turnip fb clear film plots. Differences among main-plot treatments diminished as the season proceeded from August to November in both years (Table 3). Among subplots, handweeding reduced tuber density compared with nonweeded plots both years when averaged over main plots (Table 3). Mulching with wheat straw was between nonweeded and handweeded treatments for tuber suppression. Tuber dynamics from mid-March 2005 through November 2006 in various integrated strategies are discussed below.
Fallow. In fallow, nonweeded plots, tuber density increased to >5,400 tubers m-2 by November 2006 (Figure 2a), which was higher than fallow, straw-mulched (3,683 tubers m-2) and fallow, handweeded plots (1,280 tubers m-2). Yearly tuber density remained relatively constant over 2 yr when the fallow period was followed by handweeding in bell pepper. Straw-mulched plots following the fallow period had tuber densities comparable to fallow, nonweeded plots at all sample times, except November 2006, when densities were lower for mulched plots. Tuber density in handweeded plots was lower than in nonweeded and straw-mulched plots on all sample dates. Greater than 40, 300, and 500% increase in tuber density occurred over 2 yr when fallow was fb handweeding, straw mulching, and no weeding, respectively. Hence, intensive management only during the cropping season is not sufficient for managing purple nutsedge tuber density.
Tillage. Tillage at a 3-wk interval generally caused tuber density to decline gradually from mid-March through July; however, tuber density increased to a level higher than the initial density by November of both years when subplots were not weeded (Figure 2b). A similar but lower trend occurred in most straw-mulched plots, with tuber density comparable to handweeded plots. After 2 yr, tuber density decreased by 36% in tillage plots that were subsequently handweeded compared with a 142% increase when tillage was no weeding, respectively. However, tuber density in tillage fb straw mulched plots were similar to that of tillage fb handweeded plots.
Green and Clear Film Alone. There was a sharp decline in tuber density in green film plots from March to August of each year (Figure 2c). The effectiveness of green film is evident in that no differences in tuber density were found among handweeded, straw-mulched, and nonweeded plots during August 2006. In contrast, tuber density in nonweeded plots rapidly increased once the main-plot treatments ceased in August. Green film fb straw mulching or handweeding for 2 consecutive yr reduced tuber density by 47 to 58%, but density increased 47% when no weed management followed during the cropping season. A similar trend was found for clear film (Figure 2d), with a 35% decrease and 47% increase over the initial tuber density during the 2 yr when clear film was fb handweeding, and no weeding, respectively. However, no difference was observed in tuber density when clear film was fb either straw mulching or no weeding. Use of translucent films supplemented with other control tactics has been suggested to reduce purple nutsedge density in the soil (Patterson 1998).
Turnip fb Green or Clear Film. Treatments combining the green film (Figure 2e) or clear film (Figure 1f) with turnip followed a similar trend as observed with either film alone. However, the magnitude of control was less compared with polyethylene films alone. Tuber density in November 2006 increased over the initial density when main plots were not supplemented by handweeding, regardless of polyethylene film type. Mulching with wheat straw was less effective than handweeding in managing the tuber density. After 2 yr, tuber density had decreased by 41% in handweeded plots of turnip fb green film and 25% in handweeded plots of turnip fb clear film. However, the tuber density had increased by 25% in nonweeded plots of turnip fb green film and 81% in nonweeded plots of turnip fb clear film.
Educational & Outreach Activities
Journal Article and Abstracts
Bangarwa, S. K., J. K. Norsworthy, P. Jha, and M. S. Malik. Purple nutsedge management in an organic production system. 2008. Weed Sci. (Accepted).
Chase, C.A., R.L. Koenig, J.E. Pack, and C.L. Brinton. 2007. Integrating nonchemical options to manage purple nutsedge (Cyperus rotundus) in organic vegetable production. Weed Science Society of America Abstract #290. http://www.abstractsonline.com/viewer/viewAbstract.asp
Chase, C.A., R.L. Koenig, J.E. Pack, and C.L. Brinton. 2007. Effectiveness of cultural and physical measures in suppressing purple nutsedge in organic vegetables. Proc. Southern Weed Science Society 60: 240.
Chase, C.A., R.L. Koenig, J.E. Pack, and C.C. Warren. 2006. Purple nutsedge management for organic vegetable production. HortScience 41:505.
A field day on nutsedge management in organic vegetable production was attended by more than 200 participants. Pre and post tests were provided to attendees. Thirty-six paired pre and post tests (pre and post test from the same individual) were returned. A t-test for two dependent samples was performed. The t-value was -4.94 and the p-value was <0.0001 indicating a statistically significant difference on pre and post test scores for the paired responses.
Twenty-seven attendees returned only a completed a pre-test (no post test) and 45 returned only completed a post test. A t-test for two independent samples was used to compare the scores on the paired pre and post tests with the scores on the one test only (pre or post, respectively) to see if the individuals who completely only one test differed significantly from those who completed tests. For the pre-test only group the t-value was -0.858 and the p-value was 0.394. For the post-test only group the t-value was 0.152 and the p-value was 0.879. There was no statistical difference between the “one test only” groups and the “pre and post test” group.
As a result all pretest and all post test scores were compared. A t-test for two independent samples was performed where treatment consisted of pre or post test to compare overall pre-test and post-test scores. The t-value was -5.56105 and the p-value was <0.0001. This result indicates that overall, based on mean scores only, there is a significant difference between pre- and post-test scores. Therefore, the training was effective.
Gainesville: Integration of multiple measures such as summer fallow tillage, competitive crops, and IRT mulches can be effectively used for managing purple nutsedge in organic cropping systems.
Tifton: Summer solarization is an effective, albeit drastic and disruptive technique to manage perennial nutsedges and other weeds in organic cropping systems.
Clemson: In order to reduce purple nutsedge tuber density in a heavily infested field, a year-round intensive management program should be adopted by integrating various strategies before as well as during the cropping season. Except for fallow plots, tuber density over 2 yr decreased 36 to 58% in all main-plot treatments fb handweeding, indicating that even an intensive weed management program for multiple years is not able to eradicate purple nutsedge. Purple nutsedge eradication is not technically or economically feasible; thus, efforts should be made to manage the tuber density to minimize its competition with crops (William 1976).
Annual purple nutsedge management costs calculated for each main-plot and subplot revealed that tillage was the least expensive ($145 ha-1) method for managing purple nutsedge (Table 4). Translucent polyethylene film alone was at least 4.5-fold more costly than tillage. Green film was 1.3 times more expensive than clear film, and use of turnip with any polyethylene film added $230 ha-1 in cost.
Straw mulch alone during the fall cost $729 ha-1. The addition of tillage prior to the cropping season fb straw mulch during the cropping season was the most economical means of providing season-long purple nutsedge management at a cost of $874 ha-1.
Purple nutsedge management systems involving handweeding were the most costly strategies evaluated, ranging from $6,180 to $7,671 ha-1 (Table 4). The cost was due to the hours spent handweeding bell pepper. The hours spent handweeding bell pepper was comparable among main plots involving frequent tillage or use of a polyethylene film with or without turnip, ranging from 768 to 879 hr ha-1 yr -1 (data not shown). When purple nutsedge was not managed prior to the cropping season, the time spent handweeding during the cropping season increased to 1,096 hr ha-1 yr -1, averaged over years. Hence, it is not likely that an economic return can be realized at the intensity of management put forth in handweeded plots. An alternative to reduce handweeding costs is to handweed bell pepper less frequently or to handweed only during the first few weeks after transplanting. Time of weed emergence relative to bell pepper transplanting influences the competitiveness of weeds with the crop as well as crop yield loss (Fu and Ashley 2006). However, it is possible that the tuber density during the latter portion of the cropping season may increase when handweeding ceases.
Conventional Production Costs
For conventional vegetable production, total budgeted expenses varied widely among crops and across states, from under $1,400 per acre to over $13,000 per acre (Table 5). Preharvest production costs, including field preparation, planting and crop protection, ranged from $353 to over $5,000 per acre. Harvest and marketing costs ranged from $943 to over $4,500 per acre. Fixed costs for land, machinery/equipment ranged from zero to over $3,000 per acre. Expenses for chemicals and fertilizer, which would be eliminated in organic practice, ranged from $212 to $1,955 per acre.
Organic Production Weed Control Costs
Estimated weed control costs for organic vegetable production were based on labor and materials used in experimental plots. The results shown in Table 6 represent data pooled across all crops. Note some unspecified labor for general hand weeding was equally allocated to each treatment. These expenses include activities for the summer fallow period, which was considered integral to the organic weed control practice. As an overall average, 42.2 hours per acre of labor were expended for weed control activities. Assuming a wage rate of $8.84 per hour, this represents a labor cost of $382 per acre. Total costs for weed control, including seed and fuel for some treatments, averaged $455 per acre. The Sunn Hemp cover crop treatments (mulched and disked) had the lowest time for weed control activities (30.6 hours per acre). This treatment also had quite low other expenses (seed @ $30 per acre), which resulted in the lowest total cost ($301 per acre). The tillage treatments were next in terms of labor efficiency (43.8 hours per acre) and total cost ($415 per acre). The soil solarization treatment was also intermediate in labor efficiency (42.0hours per acre), but had high expenses for plastic film ($339 per acre), resulting in higher total costs ($710 per acre). The flaming treatment was not only the least efficient for labor (56.4 hours or $498 per acre), but also had quite high costs for propane fuel ($234 per acre), resulting in the highest total cost ($732 per acre).
Yields and Value
Marketable yields and value for each crop and experimental weed control treatment are summarized in Table 7. Yields of marketable produce (meeting market grades and standards) averaged 7.8 hundredweight (cwt) for broccoli, 17.1 cwt for leaf lettuce, 16.4 cwt for bell peppers, and 93.0 cwt for squash. The soil solarization treatment produced the highest yields for broccoli and squash, and the second highest for leaf lettuce. Tillage produced the highest yield for bell peppers, and second or third highest for the other crops. The cover crop treatment (Sunn Hemp disked) provided the highest yield for leaf lettuce. Flaming provided competitive yields only for broccoli. For all treatments, yields were significantly greater than for the control (weedy) plots.
Market prices per hundredweight for these organic vegetables were estimated to range from $67.5 to $90.9, based on a 2.25 fold premium above conventional prices. Total marketable value per acre averaged $637 for broccoli, $1,152 for leaf lettuce, $1,425 for bell peppers, and $8,454 for squash. Market values per acre for the best weed control treatment were $998 for broccoli, $1,639 for leaf lettuce, $2,175 for bell peppers, and $9,221 for squash
Taking the marketable values (Table 7) together with weed control costs (Table 8), we can estimate the returns net of weed control costs for each crop and treatment, as shown in Table 8. Returns per acre net of weed control costs averaged $97 for broccoli, $612 for leaf lettuce, $885 for bell peppers, and $7,914 for squash. The tillage treatment provided the highest gross returns for broccoli, bell peppers and squash, while the Sunn Hemp cover crop (disked) was highest for leaf lettuce.
Gross Returns for Organic vs. Conventional Production
A comparison of yields, values, costs and gross returns for conventional and organic vegetable production is summarized for each of the four crops evaluated in Table 9. Marketable yields for organic vegetable production in these experiments were significantly lower than for conventional production, except for squash, in which case they were similar. Even with a 2.25 fold price premium for organic produce, the lower yields resulted in substantially reduced total value, again with the exception of organic squash.
Total preharvest production costs for organic production were estimated from the budget preharvest costs for conventional practice, less chemical and fertilizer expenses which are not used in organic production, plus organic fertilizer expense and additional labor and materials for weed control. Total preharvest costs were generally higher for organic vegetables than for conventional produce. Although chemical and fertilizer expenses were significant for conventional vegetables, the elimination of this expense was generally offset by higher costs for certified organic fertilizers (Nature Safe). Organic production also required additional labor and materials for weed control in these experiments ($540 per acre). Considering all of these cost elements together, total preharvest costs for organic vegetables were higher for all crops examined, except bell peppers. Organic preharvest costs per acre were $1,725 for broccoli, $926 for leaf lettuce, $3,470 for green peppers and $2,388 for squash. As noted before, these estimates do not include costs for harvesting/marketing or fixed costs for land and equipment, which are assumed to be the same regardless of production system.
Preharvest gross returns per acre, calculated as the difference between total crop value and preharvest production costs, were -$727 for broccoli, $713 for leaf lettuce, -$1,295 for green peppers and $6,593 for squash. In comparing gross returns per acre for organic versus conventional production, the conventional system provided significantly greater returns in excess of $5,000 per acre greater for broccoli, lettuce and bell peppers, however, for squash the organic practice produced gross returns more than twice as great and conventional production.
This research examined costs and returns for organic production with innovative weed control practices for four common vegetable crops in the southern U.S. The analysis was based upon information from experimental weed control plots together with secondary market data. In general, it can be concluded that organic production practice has lower yields and higher production costs, resulting in lower gross returns per acre than for conventional vegetable production. An important exception to this finding was for squash, which had higher yields and greater gross returns per acre for organic production. The higher prices received for organic produce in major wholesale markets was not sufficient to offset the lower yields and greater costs. This finding could be different for local farmers markets or other direct market outlets, where price premiums may be greater.
Among the organic weed control practices examined, the best yields and economic outcomes vary across crops. The tillage treatment was best for broccoli, peppers and squash, while the Sunn Hemp cover crop was best for leaf lettuce.
These results will help vegetable growers to better evaluate tradeoffs for organic vs. conventional production systems.
Areas needing additional study
Weekly tillage throughout the summer can have adverse effects on the soil. Also, rainfall during the summer may prevent timely operations. Studies are needed to determine the maximal tillage interval that would permit effective suppression of purple nutsedge.
Alternative methods to apply solarization film and cover the tractor tire tracks are needed. Otherwise, these non-solarized areas become sources of weed re-infestation. Follow-up studies are needed to explore the observation that timing of cultural practices for fall-planted crops can be manipulated and greatly suppress the presence of perennial nutsedges in these crops.
1. To test the biofumigation potential of various Brassica species in order to select best species for commercial vegetable production.
2. To test various types of plastic mulch for purple nutsedge suppression.