1994 Annual Report for AW94-033
Influence of Cover Crop and Non-Crop Vegetation on Symphylan (Scutigerella immaculata) Density in Vegetable Production Systems in the Pacific Northwest
Summary
Objectives
1. Determine the effect of specific cover crops on symphylan (a pest of vegetables) density using three cropping scenarios: fall-planted crops, no-tillage; fall-planted crops, spring incorporated (or turned under); and spring-planted crops, undisturbed.
2. Develop and test (pest) trapping techniques, using baits or attractants that may help determine symphylan density in the field and contribute to more environmentally-sound and effective means of control methods.
3. Characterize the unique community structures and key crop nutrition levels present in areas of high and low symphylan density.
4. Determine the influence of cover crops and green manures on populations of a predatory mite (or beneficial insect) of the garden symphylan, Pergamasus quisquiliarum.
Abstract of Results
Cover crops Micah barley, Wheeler rye, Monida oats and white mustard were both fall- and spring-planted, preceding sweet corn, in no-till and conventional tillage production systems. Soil samples were taken within the sweet corn row approximately six weeks after planting and again at harvest. Soil arthropods (insects and other pests) were extracted and counted from the soil samples. In one trial, the impact of cover crops on the abundance of the symphylan pest were evaluated in a traditional green manure system and a system with no spring disturbance other than opening the soil for planting (no-till). Symphylan density was decreased by spring oats, unaffected by barley, slightly increased by winter cereal rye and dramatically increased by white mustard compared to treatments without a cover crop. Plots with spring tillage had fewer symphylans than no-till plots.
In another test, cover crops were planted in late spring and desiccated with glyphosate ten days before sweet corn was planted into undisturbed cereal residues. Symphylan density was determined prior to cover crop planting, and six weeks after planting. The change in symphylan amounts from a first to second sampling period was most for cereal rye and least for spring oat crops. The change in symphylan density in the spring oats was actually less than in plots treated with the soil insecticide Dyfonate.
Several soil traps for determining symphylan density were designed and tested in the field as well. In areas with a high number of the pests, a wire mesh bag adequately attracted symphylans with a number of seeds used as bait. However, in tilled conditions, these traps were much less effective. Attempts to install permanent traps in the soil that could replace bait during the season did not work well. The best system for trapping was use of a fresh cut potato placed on the soil surface.
Soil samples were taken from two sites. At one site the grower did not apply Lorsban insecticide in one of every four rows of sweet corn. We took soil samples from areas in this row that were both damaged by symphylans and areas where corn growth was normal. This field had a history of symphylan trouble and the grower suspected that the poor corn emergence was due to the pests. However, there was a very poor correlation between the number of symphylans and the amount of damage to the corn. Interestingly, the highest symphylan population was in an area with no corn damage. However, the total number of organisms per unit volume at this site was nearly three times that of adjacent areas.
At another farm site, we took soil samples from a pumpkin field that was totally devoid of crop plants, and then compared the (soil) community structure to areas immediately adjacent that were productive. Symphylan density was highest in the affected area. Of the other soil organisms present, predacious mites were most abundant where symphylans were present, and fungal feeding springtails were most abundant where no symphylans were found. There were no differences detected between samples for bacterial and fungal biomass.
Pergamasus quisquiliarum mites were extracted from samples taken in cover crop plots. Mite densities were very low at the beginning of the season but increased steadily through November. However, this arthropod was found only where soil disturbance (spring plowing and tillage) was eliminated and cover crop residues remained on the surface. The number of P. quisquiliarum was closely correlated with cover crop biomass remaining on the soil surface.
Among other findings, these early trials found that populations of important predators such as centipedes and mites were greatest where cover crop biomass was highest. This abundance of beneficial predators was independent of the tillage system used. Cover crop residues also impacted soil microbial communities. Bacterial and fungal biomass were highest in plots with a cover crop. Microscopic analysis of roots indicated that symphylan damage to roots was less in areas with high fungal biomass compared to plots with low fungal biomass, even when symphylans were present.
Reported in 1996