Management of Garden Symphylans (Scutigerella immaculata Newport) with Crop Rotation Tactics and Improved Sampling Methods

Final Report for SW03-033

Project Type: Research and Education
Funds awarded in 2003: $160,132.00
Projected End Date: 12/31/2005
Matching Non-Federal Funds: $19,851.00
Region: Western
State: Oregon
Principal Investigator:
Jon Umble
Oregon State University
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Project Information

Abstract:

Tools for the management of garden symphylans were improved through the development of crop rotation tactics to decrease populations and refine sampling methods. Cultivation of potatoes was found to lead to a 2- to 4-fold reduction in pest populations over a broad range of conditions, with populations remaining low into the following cropping cycle. In greenhouse trials, population decreases were observed in 6 potato varieties with different alkaloid profiles. This effect was not observed with any other crops. Sampling methodology studies facilitated the development of guidelines for the efficient and reliable use of the potato baiting method.

Project Objectives:

The overall objective of this work was to improve the management of GS with improved crop rotation tactics and sampling methods.

Specific objectives were:
Objective 1 (crop rotation experiments) Evaluate the effect of a weed-free potato cropping system and a potato cropping system with a planted weed host (of GS) on GS populations and the subsequent growth of broccoli (a highly susceptible crop) in the field

Objective 2 (plant screening) Screen additional crops for activity against GS

Objective 3 (sampling experiments) Further develop the bait sampling method so it may be used effectively by growers, researchers and agribusiness

Objective 4 (damage curve development) Improve ability to interpret GS population density estimates for management purposes by developing a damage curve and action thresholds for a highly susceptible crop

Objective 5 (information dissemination) Disseminate information about biology, ecology and management of GS to a broad audience, including conventional and organic growers, extension agents and agribusiness

Introduction:

Garden symphylans, Scutigerella immaculata, Newport (GS), are key pests of the roots and other below ground parts of over 100 crops in Oregon (OR), California (CA) and Washington (WA). Eradication is unlikely since GS may retreat to a depth of several meters in the soil and persist by feeding on organic matter and other soil fauna. Consequently, latent populations cause severe economic losses in many reduced-input farming systems in OR, CA and WA. Difficulties in accurately sampling populations leads to preventative and/or improper pesticide use. Furthermore, the removal (and impending loss) of many soil pesticides poses a threat of widespread losses to GS in more pesticide-reliant systems.

The primary impetus for this project was our discovery in 2002 that under certain conditions the cultivation of potatoes greatly reduced GS populations in the lab and in a non-replicated field trial. This was a significant finding since prior to this work no crops had been documented to significantly reduce populations. Following this discovery it was of interest to further investigate this population reduction, using replicated field trials at multiple sites and laboratory trials, and to screen other crops for activity against GS. Of additional interest was to determine whether the population decrease we observed also occurred when a good host (e.g. weed species, other crop) was growing with the potatoes. This issue has broad implications, both for evaluating the effectiveness of the potato crop reduction tactic when weed hosts (of GS) are present and for evaluating other potential applications of the potato crop reduction tactic (e.g. intercrop). A complementary aspect of our work focused on sampling, a critical component of GS management. We had previously demonstrated some potential advantages of a recently developed bait sampling method over the standard soil sampling method. In this grant we examined several key aspects of this bait sampling method in order to further determine how it could best be utilized to improve GS management.

Literature Review: GS are not insects, but members of the Class Symphyla. Species of this Class are very common soil arthropods worldwide (Edwards 1958). Symphyla are small whitish “centipede-like” creatures ranging from less than 1/8 of an inch up to about 5/8 of an inch (up to 1/4 of an inch for GS). They have 6 to 12 pairs of legs (depending on age) which makes them easy to distinguish them from common soil insects (e.g. springtails) and diplurans, which only have 3 pairs of legs (all on thorax, or middle, body segment). Though their color may vary depending on what they have eaten, Symphyla are generally whiter and smaller than true centipedes which are also soil arthropods with many pairs of legs (1 pair per body segment) and quick movements.

Some Symphyla species primarily feed on dead or decaying organic matter, playing an important role in cycling nutrients (Edwards 1958). Other species, such as GS are important pests as they primarily feed on living plants (Savos 1968). Several Symphyla species are present in the Western United States (U.S.), however, GS are the only Symphyla species documented to cause crop damage in the Western U.S. GS are by far the most common Symphyla species found in Western U.S. agricultural systems.

In the Western US, eggs, adults and immature GS can be found together throughout most of the year (Berry 1972). Temperature plays a key role in regulating oviposition, and the greatest numbers of eggs are most commonly deposited in the spring and fall. Eggs are pearly white and spherical with hexagonal shaped ridges. Egg incubation period is from about 25 to 40 days when temperatures range from 50 to 70F, but hatching occurs in about 12 days as temperatures reach 77 F (Berry 1972). First instars emerge from the egg with 6 pairs of legs and 6 antennal segments. These first instars are rarely found in the rooting zone and within days molt to second instars. Each of the six subsequent molts results in the addition of a pair of legs and variable numbers of body and antennal segments. Total time from egg to sexually mature adult (seventh instar) is about 5 months at 50F decreasing to about 3 months at 70F and about less than 2 months at 77F (Berry 1972). Therefore, it may be possible to have 2 complete generations a year (Berry 1972). Interestingly, unlike adult insects which do not molt, adult GS may molt over 40 times.

GS are unable to burrow through the soil, but use pores, seasonal cracks and burrows made by other soil animals, such as earthworms, to travel through the soil profile (Edwards 1961). In general, practices that improve soil structure (e.g. addition of organic matter, reduced tillage, raised beds) improve the ability of GS to move through the soil. As a result, high populations of GS are more commonly found in fine-textured heavier soils with moderate or better structure and many macropores, than in sandy soils (Edwards 1961). In the Pacific Northwest and Northern CA GS are commonly found in alluvial soils.

Within a favorable soil habitat GS may migrate from the soil surface to a depth of over 3 feet (Edwards 1959, Michelbacher 1937). The soil profile, including compacted or sandy horizons and high water tables that may impede movement, determines the depth to which GS may migrate. Timing of vertical migrations is primarily due to the interaction among 1) moisture 2) temperature and 3) endogenous feeding cycles (cycles originating internally) (Edwards 1959). A general understanding of these interactions is important both for timing and interpretation of sampling efforts, and for selecting management tactics.

GS tend to aggregate in the top 6 inches of soil when the soil is moist and warm, and move to deeper soil strata when soil becomes very dry or cool. In OR, WA and CA, GS are generally found in the surface soil from March through November, with the highest surface populations observed in May and June. GS may be found in the surface soil under fairly warm conditions (e.g. air temperatures exceed 95 F) if sufficient moisture is present and roots are shallow or absent (Savos 1968).

GS migrate to the surface soil (root zone) to feed, then return to the deeper strata to molt, demonstrated by the large number of molted skins that are observed in these strata. When GS are feeding ravenously after molting they may enter the surface soil in generally unfavorable (e.g. hot and dry) conditions. Since migrations are not synchronized, portions of the population are usually present throughout the habitable portion of the soil profile. Presence of GS in the surface soil may also be influenced by other variables which impede movement, such as tillage and compaction from tractor tires.

Diagnosing a GS problem is sometimes difficult since damage may be exhibited in a number of forms and GS are not always easy to find when damage is observed. Economic damage may result from direct feeding to root and tuber crops and stand loss to direct seeded or transplanted crops (Berry and Robinson 1974). However, most commonly, root feeding reduces the crops’ ability to uptake water and nutrients leading to general stunting (Michelbacher 1935). Root damage may also render plants more susceptible to some soil-borne plant pathogens.

Sampling for GS is extremely important for identifying damage, making informed management decisions and evaluating the effects of management tactics. Sampling, however, is often difficult. Three main sampling methods are used: baiting methods, soil sampling methods and indirect sampling methods (Umble and Fisher 2003c). Each method has benefits and drawbacks, and the selection of a sampling method will vary depending on the objectives of the sampling (e.g. detection vs. precise population density estimation), time of year and the site conditions. Part of the difficulty in sampling results from the patchy spatial distribution of populations. To obtain information about the spatial patterns of the population, sample units are often taken in a grid pattern (Umble and Fisher 2003c). Stratification of sampling by site factors such as soil type, drainage and cropping history may provide valuable information about the distribution of populations within a site.

Soil sampling is the standard/historic method for estimating how many GS are present in a field (i.e. approximate number of GS / unit of soil, or population density estimate). Sample unit sizes vary; the most common soil sample units have been (length, width, depth) 12 x 12 x 12 in., 6 x 6 x 12 in., a “shovelful”, or cores of 3 or 4 in. diameter by 4 to 12 in. deep (Umble and Fisher 2003c). When soil samples are taken, the soil from each sample unit is usually placed on a dark piece of plastic or cloth where the aggregates are broken apart and the GS are counted (Berry and Robinson 1974). Sampling must be conducted through the entire habitable region of the soil profile (i.e. possibly to a depth of over 3 feet) to obtain absolute population density estimates, but this is rarely done for management purposes because of the extensive time and resources required (Michelbacher 1937). Therefore, sampling is usually conducted when GS are present in the top 6-12 inches of the root zone (Umble and Fisher 2003c).

In recent years, bait sampling methods have been developed (William 1996). Bait samples are generally much faster to take than soil samples, but they are also more variable (Umble and Fisher 2003c). To bait sample, a 1/2 sliced potato or beet is placed on the soil surface and sheltered with a protective cover (e.g. white pot or 4″ PVC cap). Baits are generally checked 1 to 5 days after placement. Baits are checked by lifting the bait and counting first the GS on the soil and second the GS on the bait.

Management of GS can be difficult. For management purposes it is important to make a distinction between tactics that decrease populations and tactics which reduce damage to crops, but may not necessarily decrease populations. In most cases, effective garden symphylan management involves establishing a balance between these two strategies. It is important to note that in most cases little can be done after damage is noticed, without replanting. Sampling is, therefore, important in determining the proper course of action.
No simple, inexpensive, and completely reliable method of controlling symphylans has been developed. Tillage is probably the oldest control tactic used, and is still one of the most effective. Tillage can physically crush garden symphylans, thus reducing populations (Michelbacher 1937). Tillage may also detrimentally decrease populations of key garden symphylan predators such as centipedes and predaceous mites. However, in annual cropping systems, benefits of increased predator populations (from reduced tillage) have not been shown to be as effective as tillage in decreasing garden symphylan populations (Peachey et al. 2002).

In conjunction with tillage, pesticides are commonly used to manage garden symphylans. Plant protection is probably achieved by direct mortality as well as repelling symphylans from the root zone. Pesticides are most effective if applied before planting as broadcast and incorporated applications (Berry and Robinson 1974). Banded/incorporated applications may provide acceptable protection for some crops. In some perennial crops, such as hops, post plant pesticide applications can reduce symphylans sufficiently to promote plant vigor. Fumigants and organophosphate and carbamate pesticides have historically been the most effective, but many are no longer registered for symphylans in many crops (Berry and Robinson 1974).

Garden symphylans can feed on a wide range of plants, and can persist in even fallow soil. Plants may vary greatly in their suitability for garden symphylan population development (Umble and Fisher 2003a). Crop rotation may partially explain seemingly sudden shifts in garden symphylan populations. Populations have been shown to decrease significantly in potato crops (Umble and Fisher 2003a). Populations have also been found to be lower after a spring oat (‘Monida’) winter cover crop than after a mustard (‘Martiginia’), barley (‘Micah’) or rye (‘Wheeler’) winter cover crop (Peachey et al. 2002).

Most plants can tolerate some level of garden symphylan feeding during all or part of the growing season and numerous tactics can be used to successfully grow healthy crops in garden symphylan infested soil (Umble and Fisher 2003b). Susceptibility to garden symphylan feeding can vary dramatically among different plant species and varieties. Generally, smaller seeded crops tend to be more susceptible than larger seeded crops (Umble and Fisher 2003b). Commonly damaged crops include broccoli and other cole crops, spinach, beets, onions and squash. Beans and potatoes are rarely damaged even under high garden symphylan populations. Perennial crops, such as strawberries, raspberries, blueberries, hops and bare root trees can also be damaged, particularly during establishment (Berry and Robinson 1974). Within a crop, susceptibility is often related to stage of the crop planted. For example, direct seeded tomatoes are generally more susceptible than transplants. Broccoli transplants, conversely, often fail to establish under high garden symphylan populations (Umble and Fisher 2003b).

Garden symphylans are quite active and surprisingly mobile for their size, moving vertically and horizontally through the soil profile. They rely on soil pores and channels made by roots and other soil organisms, to move through the soil. Therefore, access to roots is strongly correlated with soil structure, bulk density or “fluffiness” of the soil and pore connectivity. Some tactics focus on temporarily reducing the number of garden symphylans in the surface soil then planting, thus allowing these plants to establish while garden symphylan densities are low. Tillage is an important tactic for decreasing populations in the surface soil. Along with directly killing garden symphylans tillage breaks apart soil aggregates, modifying soil pores and pore connectivity. The effects of tillage may vary with type of implements used. In general, the more disruptive the tillage the greater effect this tillage will have on garden symphylan movement and feeding. Plowing or discing, followed by thorough preparation of a fine seed bed using a rotiller or roterra often reduces surface feeding garden symphylan populations for 2-3wks (Umble and Fisher 2003a).

Cooperators

Click linked name(s) to expand
  • Tom Denison
  • Mike Dickman
  • Rex Dufour
  • James Fisher
  • Mendel Friedman
  • Fisher Glenn
  • Jack Gray
  • Peter Kenagy
  • Jim Leap
  • Daniel McGrath
  • James Todd
  • Mark VanHorn
  • Michelle Vesser

Research

Materials and methods:

Objective 1 (crop rotation experiments):

The effect of three treatments: 1) a weed-free potato cropping system 2) a potato cropping system with a planted GS host (broccoli or sweet corn depending on site-appropriateness) and 3) a control (broccoli or sweet corn), on GS were investigated at 4 sites with historic GS problems using a randomized complete block (i.e. site = block) experimental design with 3 within-block replications at 3 of the 4 sites. Treatments (crops) were applied in year 1, and in year 2 all plots were planted to a broccoli indicator crop.

Site Descriptions: The 4 sites were farms with connections to the major participants. Two of the farms are organically managed: 1) University of California at Davis Student Experimental Farm (UCD) and 2) University of California at Santa Cruz, Center For Agroecology and Sustainable Food Systems Farm (UCSC), and two of the farms are conventionally managed: 3) Oregon State University Horticulture Farm, Corvallis, OR (OSU) and 4) The Kenagy farm, Albany OR. At each site, an infested area to conduct the trial was identified by sampling fields with historic GS problems in the spring of year 1. Plots were delineated so that they had as similar populations as possible. Treatments were subsequently randomly applied to plots. Plots were from 30-35 feet/ side depending on site.

Plot Management: Plots were managed as similarly as possible among locations (e.g. tillage, irrigation, fertility management). Management was also maintained consistent among treatments within each site.

Evaluation of Effect of Treatments on GS : GS populations were estimated at each site before, during and after the cultivation of each crop using potato baits (20 sample units / plot). Treatment effects were evaluated by using Analysis of Variance (ANOVA) to test for differences in the estimated GS densities among the treatments at 2 critical periods, immediately following the harvest of the first crop (potato, intercrop, cash crop) and near the planting of the indicator (broccoli) crop.

Evaluation of Indicator (broccoli) Growth: The growth of the broccoli crops in year 2 was evaluated by estimating the total number and dry weight of plants in a 20’x 20’ area in the center of each plot. Dry weights were calculated by first measuring the wet weight of the plants in each area, then converting to dry weight using an oven-dried subsample.

Objective 2 (plant screening):

Stage 1. In Stage 1 we investigated likely alkaloids (compounds present in potatoes) related to the observed decrease in GS populations in potato, with intent that this investigation would aid in selecting additional crops to be screened for activity against GS in the greenhouse (Stage 2). Cohorts of 5 GS in 100 mm (diameter) containers were used as experimental units. The two predominant potato alkaloids, alpha-solanine and alpha-chaconine were tested for repellency and toxicity to GS at 4 concentrations (0, 341, 1251 and 2918 PPM) when dissolved in DMSO and applied to 0.4” diameter lettuce leaf discs. Repellency was evaluated by measuring the amount of feeding to treated lettuce leaves (loss by weight) after 7d in choice / no-choice assays. Toxicity was evaluated by measuring GS survival in treatments after 8wks, when treated leaves were replaced each week.

Stage 2. Forty crops (or varieties) were screened for activity against GS in the greenhouse in four separate trials over the two year period. The suitability of each crop (or variety) for GS population development was evaluated by establishing crops in pots (7 reps), infesting with 35 GS and measuring the change in population density after 8 wks. ANOVA was used to test for differences in GS densities among treatments after this period.

Objective 3 (sampling experiments):

At the initiation of this grant, considerable advantages (time efficiency) of the potato bait sampling method over the standard soil sampling method had been recently documented. The baiting method, however, sometimes provided inconsistent results for unknown reasons limiting its utility for many applications. Consequently, though this method showed great potential, it was unknown under what conditions it could be used effectively.

It was our goal to identify conditions under which the bait sampling method could be used effectively and reliably. In the initial stages of this grant we conducted extensive exploratory sampling to identify factors on which to focus our efforts. Based on these exploratory sampling efforts, we focused our efforts on investigating the relationship between population densities estimated using the recently developed potato bait method (1/2 potato left out for 1 day) and population densities estimated using 1) a smaller bait, 2) a longer baiting duration and 3) population estimates determined using soil cores (i.e. calibration).

For each of these 3 relationships, 5-10 sites with a range of GS populations were sampled using both baits and soil cores starting on the same day (and time of day) during, April, May and June, the time period when sampling for management purposes commonly occurs. All sites had sparse or no vegetation. Forty to 50 sample units (baits or soil cores) were used for each sampling method on each sampling date.

Objective 4 (damage curve development):

In order to develop a crop damage curve for a highly susceptible crop (i.e. broccoli), we described the relationship between GS densities in the broccoli indicator plots (objective 1), estimated at the time of planting using bait sampling, and the percent of the targeted plant population (thinned density) population remaining at harvest using nonlinear modeling techniques.

Objective 5 (information dissemination):
1) Conduct on-farm grower field days, including information about our research, discussion, and additional literature about GS biology, ecology and management.
2) Update and expand the section addressing GS in the Pacific Northwest insect management handbook.
3) Present research results at meetings/workshops that growers attend.
4) Continue work with electronic-forms of information dissemination by getting the GS website up and running
5) Publish articles in 3 written-media sources that routinely carry articles covering gardening and agriculture

Research results and discussion:

Objective 1 (crop rotation experiments):

Potatoes successfully reduced GS populations across all sites. The treatments had a significant effect on GS populations immediately following harvest the first season (F2,24, P = 0.03). Populations at this time were 2.6 times (95% CI from 0.21 to 4.9 times) lower in the potato treatment than in the control (Fig.1). Populations in the intercrop treatment, were numerically lower on average than the control at all sites (Fig. 1), but were not significantly different.

The magnitude of the effect of the potatoes appeared to increase up to the time of planting of the indicator crop (3-6 months following harvest of the first season). Differences between the control and other treatments at this time were greater than those observed immediately following harvest (F2,24, P < 0.001). At this time, populations were 3.9 times (95% CI from 1.9 to 6.0 times) lower in the potato than in the control. Populations in the intercrop were 2.9 times lower (95% CI from 0.94 to 5.0) than in the control (Fig. 2). This objective provided extremely important information about an effect that had previously been observed only in the laboratory and in a non-replicated field
trial. The effect of potatoes on GS was reasonably consistent across a range of conditions (4 sites, variable soils, irrigation, equipment, climate, planting date, etc..), significantly decreasing populations at all sites. At each site, variability was observed among plots (e.g. control plots with low populations, potato plots without as great a decrease in GS populations), likely owing to a number of factors including non-homogeneity of populations at the start of the experiment, edge effects and tillage effects. Populations were significantly reduced in the intercrop plots which indicates that considerable population decreases can result even with abundant “good” host plants available to the GS. This study does not directly elucidate the specific mechanism leading to the population decrease, but it does suggest that the decrease is either related to the GS feeding directly on the potato roots, or that the potatoes are somehow modifying the soil environment unfavorably for the GS.

Objective 2 (plant screening):

Forty-two crop species and/or varieties were screened over a two-year period in the greenhouse for activity against GS. Crops/varieties were selected based on grower and researcher observations and scientific literature. Along with 6 potato variety treatments, with different alkaloid profiles and a control (no plant) treatment, crop treatments included varieties of: annual ryegrass, barley, endophytic fescue, nonendophytic fescue, oats, orchardgrass, perennial ryegrass, wheat, California poppy, broccoli, sweet corn, eggplant, French marigold, garden huckleberry, lettuce, Mexican marigold, mustard, sudan grass, snap beans, garlic, meadowfoam, phacelia, rye sunflower, sordan. Six potato varieties and two intercrops (potato + corn or broccoli) consistently reduced populations by greater than 75% (Fig. 3). No other crops provided significant control (Fig. 3). Additionally, in Stage 1 laboratory screening no significant differences were observed in GS feeding or in GS mortality across alkaloid compounds and concentrations.

We infer from these results that the effect of potatoes on GS was not strongly related to potato variety. Significant decreases were observed on all potato varieties screened, several of which had dramatically different alkaloid profiles. This confirms what we have observed in the field (i.e. decreases have been observed regardless of variety). No effect of feeding or mortality was observed when the two predominant alkaloids (alpha-solanine and alpha-chaconine) were presented to GS in the laboratory at a range of concentrations.

Objective 3 (sampling experiments):

Our goal was to identify conditions where the bait sampling method could be used reliably and effectively. Success was primarily evaluated by comparing bait sampling results with soil sampling results. We, therefore, wanted to identify conditions that led to a consistent relationship between the population of GS estimated using the baits and the actual population of GS in the soil. Problem situations were noted when GS were found using soil sampling, but were not collected on baits, since this would lead to misdiagnosis of an infestation. In the initial stages of this grant we conducted extensive exploratory sampling using both methods to identify factors on which to focus our efforts.

The results of our exploratory sampling indicated that a number of factors likely influenced the baiting method in some cases. These factors included the presence of vegetation, soil temperature, time of day, soil moisture, bait size, and baiting duration. Quantifying the significance of the presence of vegetation was of particular interest since sampling is often conducted when plants are present. However, after sampling numerous vegetated sites it became evident that this was a highly complex issue since vegetation likely interacted with a number of other factors such as soil moisture and crop species. In several cases GS populations estimated using baits were extremely low when soil sampling indicated that many GS were actually present in the soil. Similarly, differences in soil temperature and soil moisture also appeared to lead to inconsistencies. Because of the complex nature of these interactions, we focused our efforts on developing recommendations for the baiting method under commonly used “targeted sampling conditions” where the effects of vegetation, soil temperature and moisture were minimized and did not confound sampling results. These targeted sampling conditions were: 1) no or very sparse vegetation present 2) at least 3wks following tillage 3) sufficient soil moisture and temperature for growth of annual vegetables in the spring (April – June).

Under these targeted sampling conditions we examined the relationship between population densities estimated using the potato bait method (~5 oz potato piece left out for 1 day) and population densities estimated using 1) a smaller bait (~2.5 oz), 2) a longer baiting duration and 3) population estimates determined using soil cores (i.e. calibration).

When sampling within the targeted sampling conditions at 10 sites using both methods, a reasonably strong (R2 = 0.67) linear relationship was identified between the estimated number of GS per square foot (to a depth of 6”) and the estimated number of (log transformed) GS per bait (Fig.4). From this observed trend we conclude that the development of targeted sampling conditions successfully reduced much of the variability and inconsistencies observed in our exploratory sampling (conducted under a wide variety of conditions), and that when the baiting method is used within the targeted sampling conditions, results can be reliably related to the “true” number of GS present in the soil.

Decreasing the bait size from a 5 oz to a 2.5 oz bait had no effect on GS population density estimates when 5 sites were sampled using both methods. A strong (R2 = 0.99) 1:1 relationship was observed between the population density estimates obtained using the two bait sizes (Fig.5). From this we conclude that it is possible for bait sizes to vary (from 2.5 – 5 oz) without influencing sampling adversely. This may decrease sampling costs, as well as the weight of sampling materials in the field.

The effects of baiting duration (i.e. how long the bait was left on the soil before checking) were more complex. We knew from our exploratory sampling efforts that in July and August, the number of GS per bait generally decreased when baits were left on the soil for greater than 1 day, though we did not focus our efforts on examining this closely, since growers rarely sample during these months. Within our targeted sampling conditions (April – June), however, this trend was reversed (Fig.6). The data were variable, but on average approximately twice as many GS were collected by leaving baits out for 3 days as compared to the standard 1 day in a trial conducted at 5 sites.

Objective 4 (damage curve development):

Results from this study suggest that considerable GS damage can result from relatively low populations, and action thresholds for the baiting method are likely similar to those used for direct soil sampling (i.e. ~5 GS/ft3). The percent of the targeted plant population (broccoli indicator crop) remaining at harvest decreased sharply with increasing GS populations increased (Fig. 7). A nonlinear curve describing this relationship predicted a decrease of 60% in the amount of plants remaining at harvest as populations increased from 0 to 8 GS per bait (Fig. 7). Overall, populations were generally lower at all sites in 2005, thus higher population densities (i.e. >10 GS/ bait) are not well represented in this study. However, populations in commonly observed range of populations (i.e. 0 to 5 GS/bait) are very well represented.

Objective 5 (information dissemination):

See “publication and outreach section”

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Berry, R. E. and R. R. Robinson. 1974. Biology and control of the GS. Oregon State University. Extension Service. Extension Circular 845.

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Research conclusions:

We were successful in accomplishing many aspects of our primary goals of improving sampling methods, increasing interpretability of sampling results and development of crop rotation tactics to decrease populations. Specific key results/outcomes of this work were: 1) the identification of specific conditions where the bait sampling method could be used to provide consistent results, 2) improved understanding of the “meaning” of bait sampling results through the development of a damage curve 3) determination of the effect of key crops on GS populations under a number of different conditions and 4) dissemination of information concerning GS sampling and management to a broad range of end users.

Prior to our work, the greatest drawback of the bait sampling method was that it yielded erratic results for unknown reasons, which led to an unacceptable level of risk for many growers and crop consultants. The recommendations we have developed have greatly improved the consistency of the method. We did not succeed in identifying a simple reliable method that will work in all situations; we still recommend the use of soil sampling under a number of conditions. However, knowing the correct tool for a given set of conditions greatly improves sampling efficiency while reducing misdiagnoses. Much of the pre-plant sampling in conventional cropping systems will likely continue to use soil sampling methods. The increasing use of baiting by crop consultants, organic growers and researchers may have a number of significant impacts: 1) correct diagnosis of damage and selection of management tactics, 2) reduction of pesticide applications from common misdiagnoses (e.g. slugs and craneflies) 3) reduction of damage in organic systems by sampling before planting.

The impact of our crop rotation work is closely tied to our work in disseminating information, and advancement of sampling methods. We have conclusively demonstrated that potatoes have an extremely strong negative effect on GS populations under a broad range of conditions. Where appropriate, the inclusion of potatoes in rotations, before highly susceptible crops has effectively reduced damage in a number of farms where GS have been a major problem. Unfortunately, the use of potatoes in a rotation to decrease GS populations is only economically feasible for a limited group of small scale and organic growers. Likely of greater impact, this work has highlighted the dynamic nature of GS populations, and the subsequent opportunity for growers and crop consultants to approach GS management differently. New approaches are founded in the understandings that changes in populations can be predicted to some extent, damage is influenced by a number of factors including crop rotation and effective use of sampling methods provide a method for evaluating the effects of plants on GS. The impact of these new approaches has already become evident in new innovative approaches that a number of growers have already initiated at their own farms, such as dramatically decreasing pesticide usage by spot treating individual hotspots, planting “indicator crops” to identify the location of infestations and manipulating factors such as planting date, plant density, and soil compaction to decrease damage.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Refereed Publications:
1. Effect of GS on Bare Root Trees in Oregon (submitted)
2. Crop rotation effects on GS (in preparation for submission)
Other written publications:
1. Pacific Northwest Insect Management Handbook, revision of GS section
2. IR4 Newsletter Vol. 35:3, 2004
3. Featured Article: OSU Extension Service
4. Website publication: ATTRA/NCAT

Information Dissemination Talks/Field Days:
2006 Pacific Northwest Insect Management Conference, Portland, OR
2006 Oregon Processed Vegetable Commission Meeting, Salem OR
2005 Oregon Horticulture Society, Vegetable Section, Salem OR
2005 Octoberpest, sponsored by North Willamette Extension Center, Aurora, OR
2005 Oregon Hop Commission Meeting, Wilsonville, OR
2005 Hop Field Day, Northern Willamette Valley, OR
2005 OACFA Safety and Stewardship Seminar, Eugene, OR
2005 OACFA Safety and Stewardship Seminar, Wilsonville, OR
2005 Oregon Seed Growers League, Portland, OR
2005 Western Farm Service Grower Meeting, Tangent, OR
2005 Oregon Annual Ryegrass Growers Meeting at Ag Expo, Albany, OR
2005 Oregon State University Department of Horticulture Seminar Series, Corvallis OR
2004 USDA/ARS Crop Improvement and Protection Research Unit Seminar Series, Salinas CA
2004 Oregon department of horticulture field day, Corvallis OR
2004 6th Annual Small Fruit Growers Workshop, Vancouver, WA
2004 “Bug Fair” sponsored by OSU Integrated Plant Protection Institute, Corvallis, OR
2004 Oregon Seed Growers League, Portland, OR
2004 Oregon Ag. Chemical and Fertilizer Association Seminar, Eugene OR
2004 Oregon Ag. Chemical and Fertilizer Association Seminar, Wilsonville OR
2004 OSU Crop and Soil Science extension personnel field day, Corvallis, OR

Project Outcomes

Project outcomes:

Use of potatoes to Decrease Populations:
Costs: in many agricultural systems, growing potatoes is not economically feasible, growing potatoes would not be profitable for use only to decrease populations, if potatoes are not marketable.
Returns: when economically feasible, significantly decrease GS populations and grow susceptible crops with very low risk from damage from GS.
Risks: effect of potatoes on GS has been extremely consistent (with plot sizes used in our studies), most of the risk involves economic profitability of growing potatoes.

Use of bait sampling methods:
Costs: Sampling fields (up to approx. 60 acres) commonly takes between 2-6 hours and may cost several hundred dollars if conducted by a professional agricultural consultant. Time costs may also be significant for growers with tight planting windows since sampling may delay planting, or require growers to modify timing of tillage operations
Returns: Where pesticides are currently used preventatively, knowledge about populations allows informed decisions to be made concerning pesticide applications which may lead to reduction cost and amount of product applied (e.g. spot treatments, or avoiding treatments). For organic growers, sampling may greatly reduce damage by helping growers identify the location infested areas, and to manage these areas accordingly.
Risks: Interpretation of sampling results has been greatly improved, but still has risks. Populations are often very patchy, and damage may still be observed in some areas in fields when pesticides are not used. Other risks in sampling are largely related to ensuring sampling is conducted when conditions are favorable (e.g. populations are at the surface). When sampling is conducted in non-ideal conditions (which is inevitable) sampling results are more difficult to interpret.

Potential economic impact of this work includes:
– Conventional system: economic savings and reduction of environmental impact from reduction of “inappropriate” pesticide applications from misdiagnoses (as crop consultants increasingly adopt bait sampling for diagnosis), and reduction of pesticide rates (as growers become more comfortable with results from sampling methods and spot spraying becomes viable)
-Small-scale and organic systems: economic savings from the reduction of damage through the use of potatoes in rotation to decrease populations and damage
-All cropping systems: savings from the reduction of damage through the use of sampling methods, and subsequent selection of appropriate sampling methods

Farmer Adoption

The greatest adoption/modification in the area of sampling methods, associated with our work, has been with conventional crop consultants in the Willamette Valley in OR, and with organic farmers in CA and OR. Most growers and consultants understand the great need for effective sampling methods and have been eager to experiment with baiting. When used under correct conditions in infested soils, growers and consultants have been very enthusiastic about being able to effectively diagnose damage and determine the size and location of hotspots, and relative differences in populations. We anticipate adoption of bait sampling methods will continue as the risk associated with this method decreases.

Adoption of crop rotation tactics (i.e. use of potato in rotation to decrease GS populations) is generally limited to some small-scale and organic growers; therefore direct adoption of this tactic is not extensive. However, as mentioned above, this work has directly led to the adoption of a new perspective that views GS populations as dynamic and highly complex, influenced to some degree by numerous management tactics. Adoption of this viewpoint has led to a number of innovative management strategies, such as spot treatments, directed tillage operations, timing of cover crop incorporation and numerous others. Sampling allows growers to measure these influences.

Recommendations:

Areas needing additional study

-Sampling to understand seasonal vertical migrations
-Study of populations in perennial crops
– Development of methods to use baiting in the summer
– Development of a smaller soil sample unit (standard is 0.5 cubic foot)
– Continued screening of other crops for activity against GS

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.