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

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

Summary

In our first year, we tested fall-planted cover crops (bare control, rye, rye/vetch, crimson clover, oats) and spring-planted cover crops following a fall oat crop (bare, spring oats, oat/field pea, annual ryegrass, rape). Strips of each cover crop were plowed and planted or strip-tilled and planted in sweet corn. Effects of the cover crops on weeds, insects, microbial densities were measured. Our method of strip-tilling increased microbial densities in rhizosphere soil, but allowed too much regrowth of the cover and weeds, which competed with the corn so that there was no marketable yield.

Objectives/Performance Targets

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 movement out of the cover crops.

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

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.

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

Impacts and Contributions/Outcomes

In fall 2000 through spring of 2001, we planted seven randomized complete blocks with ten different cover crop treatments. Those planted in the fall were rye, rye/vetch, wheat, oats, and an unplanted bare ground control. Oats were also planted in the fall to winter-kill in the plots where spring covers were planted. The spring cover crops were: annual ryegrass, spring oats alone, spring oats with field pea, and rape. Crossing these ten cover crop treatments were three management treatments: 1) plowed and planted with sweet corn (with fertilizer added according to soil tests in each plot); 2) strip-tilled and planted with sweet corn with periodic mowing of the vegetation between the rows; and 3) mowed and then allowed to grow to maturity, with no summer crop planted.

Plant measurements: We assessed the cover and biomass of the cover crops twice during the spring, and also assessed the weed cover and identified weed species twice. The rye/vetch, rye alone, and wheat cover crops were still covering the plots densely and smothering nearly all weeds on May 8 and June 11. The winter-killed oats was still covering the ground as a mulch and providing effective weed suppression on May 8, although the weeds were emerging by June 11. Except for annual ryegrass, the spring cover crops following oats did not substantially improve weed suppression. The strip-cropping method did not manage regrowth of the cover crops and weeds effectively. Due to competition with the weeds and regrowth of cover, there was no marketable sweet corn yield in the strip-cropped plots. There was no significant difference in yield among the cover crop treatments in the plowed plots.

Insect measurements: We assessed insect activity in the cover crop plots using emergence cages in late spring, pitfall traps through the summer, and sweep and vacuum samples through the summer. We also sampled pitfall traps weekly on 3 cooperating farms in order to collect and identify species of wireworms (elaterid beetles) present.

Microbial measurements: Microbial densities from soil cores removed from cover crop soils on 1 June had elevated levels of total bacteria in soil cropped to rye. Deleterious manganese-oxidizing microbes were increased in clover, rye, rye/vetch, and wheat soil. Manganese-reducing microbes, which are presumed to be beneficial, were increased in soil cropped to clover and wheat. However these trends were not seen in later samples. Levels of beneficial microbes, such as the fluorescent pseudomonads, and deleterious microbes, such as the Mn-oxidizing microbes, were both in greater densities in rhizosphere soil from strip-tilled plots than from plowed corn plots.

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