Benefits - Drawbacks of Various Winter Cover Crops in Vegetable Pest Management

Benefits - Drawbacks of Various Winter Cover Crops in Vegetable Pest Management

Summary

Winter cover crops improve the sustainability of vegetable farms in the Northeast because of their beneficial effects on soil quality and nutrient management. However, the effects of cover cropping practices on insect management and on plant disease management are not well understood.

This project studies interactions between cover crops and selected beneficial and pest insects and arthropods. Targeted insect pests are tarnished plant bug and potato leafhopper, which are known to move from cover crops to main season crops, and the wireworm complex, which carries over from year to year in the soil, and thus might be affected by cover crops. Additionally, the project studies the interactions between cover crops and soil-dwelling bacteria affecting plant health.

Objectives/Performance Targets

1. Measure the density of selected insect pests and generalist arthropod predators over time in seven winter cover crops in the field. Determine what effects cover crop management might have on their survival and on movement out of the cover crop.

2. Evaluate the growth and survival of wireworms on roots of cover crops in the laboratory, and determine the effect of cover crop residues incorporate into field soil on their growth and survival.

3. Examine the effect of winter cover crops on diversity of plant-growth-promoting bacteria and deleterious bacteria in the rhizosphere of the cover crop and on the subsequent crops.

4. Isolate bacteria associated with wireworm mortality and examine their effects on plant root health.

Accomplishments/Milestones

In the fall of 2000 and 2001, cover crops of rye, rye/vetch, crimson clover, oats, wheat, (and in 2001 rape), and a bare control were established, and in spring 2001 and 2002, spring cover crops were planted into the oats (which winter killed in the winter of 2000-2001, but not in 2001-2002). Spring cover crops were annual ryegrass, oats, oats + field pea, or a bare control. Rape was used as spring cover crop the first year, but put on very little biomass and went quickly to seed. In the second year, it was planted in the fall, and overwintered successfully. We assayed cover crop and weed biomass in the plots once in spring of 2001 and twice in 2002.

Beneficial and potential pest insects in cover crops were evaluated using pitfall, sweep, and vacuum samples. Rhizosphere populations of microbial groups were assayed using ten-fold dilutions spread onto plates of 10% Tryptic soy agar, King’s B agar, and Mn-dioxide agar for estimating total bacteria, fluorescent pseudomonads, and Mn-transforming bacteria.

Wireworm studies have been delayed due to the difficulty of accumulating adequate numbers of wireworms. After several unsuccessful attempts to collect wireworms at our experimental farm, we began collecting them from a severely infested garden plot, and have been accumulating them in cold storage to get enough to do experiments.

Impacts and Contributions/Outcomes

Results from the 2001 sweep samples for insects:

Of the potential pests, potato leafhopper adults (Empoasca fabae) moved into the rye/vetch plots at much higher levels on June 19, June 25, and July 3 than in all other plots. Tarnished plant bug adults and nymphs (Lygus lineolaris) were more abundant in the bare control (living in weeds) and in rye/vetch than in the rye and wheat plots through all June samples. Thrips (species not distinguished) were more abundant in rye and wheat than in other crops in the samples from June 8 and 19, and were more abundant in rye/vetch, wheat, and annual ryegrass on June 25. Among beneficial insects, syrphid flies were more abundant in annual ryegrass than other crops on July 3. Adult Orius bugs were more abundant in rye/vetch plots than all other plots on June 25 and July 3.

The results from assays of rhizosphere microbes found that bacteria were increased 5-fold under rye plus vetch compared to wheat. However, there was no difference between soils left bare and soil cropped to rye plus vetch. Fluorescent pseudomonads and Mn-transforming microbes were not affected by cover crop in 2002.

Collaborators: