Influence of Cover Crop Vegetation on Symphylan (Scutigerella immaculata) Density in Vegetable Production Systems in the Pacific Northwest

1996 Annual Report for AW96-019

Project Type: Research and Education
Funds awarded in 1996: $0.00
Projected End Date: 12/31/1998
Matching Federal Funds: $7,860.00
Matching Non-Federal Funds: $3,000.00
Region: Western
State: Oregon
Principal Investigator:
Ray William
Oregon State University, Dept. of Horticulture

Influence of Cover Crop Vegetation on Symphylan (Scutigerella immaculata) Density in Vegetable Production Systems in the Pacific Northwest


1.Characterize arthropod and microbial community structure and trophic level changes (temporally and spatially) due to cover cropping and tillage practices in sweet corn cropping systems with specific reference to symphylans, beneficial arthropods and potential predators of symphylans in both microplot and on-farm research.
2.Evaluate cover crop and tillage impacts on weed population dynamics and sweet corn yield.

Tillage and cover crop effects on arthropod and weed communities were determined in vegetable cropping systems. Cover crops were fall-planted preceding sweet corn in fall (direct seed) and spring (conventional tillage) systems in microplots at the OSU research farm in the third of three years. An on-farm trial compared fall-planted cover crops preceding squash in a spring tillage system. Soil samples for arthropod extractions were taken at three times: 1) before crop planting, 2) at canopy closure and 3) at harvest. Soil arthropods were extracted and counted from the soil samples with Berlese funnels. Symphylan traps were placed on the soil surface next to each soil extraction site and symphylan abundance was evaluated weekly throughout the season. The effect of cover crops on winter weed survival, summer annual weed emergence and sweet corn yield was determined.

Symphylans were least abundant in the Micah barley and oat plots in the on-farm trial with conventional soil tillage to incorporate the cover crop residues. Symphylans were most abundant in the common vetch plots. These results follow those of previous years and studies indicating that small grain cover crops such as Micah barley and Monida oat have the greatest potential to reduce symphylan populations in conventional tillage systems. However, in the same trial, we found that Diabrotica larvae (a root feeder on many crops) were more common following small grain cover crops than in the legume treatments of common vetch and crimson clover.

Microplot on-station research indicated that symphylan abundance during the sweet corn growing season was lowest following small grain cover crops of Wheeler rye and Monida oats in both conventional tillage and direct-seed systems. Symphylans were most abundant in the Micah barley and direct-seed systems that were not tilled in the spring before sweet corn planting. The ratio of macro predators to symphylans followed the trend of previous years with the highest ratio in the rye and oat cover crop treatments. Fungal biomass in the soil was greatest in the rye plots and lowest in the fallow treatments.

Nightshade and pigweed emergence was reduced by 90 to 100 percent by eliminating all spring tillage before sweet corn planting and direct-seeding through cover crop residues. When the soil was tilled before planting sweet corn, weed emergence was much greater regardless of cover crop type or residue biomass. In direct-seeded treatments, total weed emergence averaged two seedlings per m sq. whereas in the conventional tillage treatments emergence averaged 81 seedlings per m sq. Sweet corn yield in the direct-seed treatments was comparable to that of the conventional tillage plots, although average ear wt. of the direct seed treatments was 6 percent lower than the conventional tillage treatments.

Potential Contributions
Cover crops provide a source of carbon and energy for soil ecosystems. This energy may be used to restructure arthropod communities to the benefit of the crop and farming systems. Our data indicates that populations of several potential predators of symphylans may increase when moderate amounts of cover crop biomass are designed into the system. In some situations, symphylan populations have declined where cover crops were used. This could dramatically reduce the amount of pesticides routinely used to control symphylans in vegetable crop rotations.

Fall tillage with direct seeding (cross-slot planting) sometimes reduces the number of field operations in the spring for planting vegetables such as sweet corn. In other research, we have demonstrated that reduced cultivation and herbicide rates can be integrated. However, farmers must learn a completely new production system, often requiring a substantial investment of time and resources over several years.

Farmer Adoption and Direct Impact
Changes in practice. Integration of cover crops is increasing among farmers, but use is constrained because of perceptions that cover crops add management complexity and cost to systems that already have low rates of return. Long-term benefits are outweighed by the immediacy of current economics. If symphylan populations can be manipulated by cover crop components, this will provide an additional incentive to adapt cover crop strategies. Specifically, soil insecticide and herbicide use may decrease and allow more selective pesticide usage that would minimize impact on other important soil predators and vegetable rotations. The result may be multiple consequences and tradeoffs that encourage growers to make knowledgeable choices.

Our purpose involves determining consequences or impacts of fall and spring tillage systems on various biological components of soil systems; not to recommend. However, evidence suggests that cover crops may either increase or decrease symphylan populations, depending on cover crop species and growth pattern. Growers should carefully consider the type of cover crop based on these findings. More important is the observation that many important generalist predator populations are enhanced by adding cover crops during the fallow season or by minimizing early season tillage disturbances.

Farmer Comments
Producer involvement has been principle in giving direction to the research trials. This had included design of the trials, selection of cover crops and evaluation of results. University personnel have primarily been involved in data collection. This involvement has led to some non-traditional approaches. For instance, in the on-farm trial, the participating grower suggested that cover crop treatments that apparently reduced symphylan populations in 1996 be planted on plots that were previously planted to cover crops that increased symphylan abundance. Even though this confuses long-term analysis of the successive effects of the same cover crop from year to year, it emphasizes the priorities of the producer; i.e., positive and immediate effects on arthropod communities.
Reported in 1998