Benefits - Drawbacks of Various Winter Cover Crops in Vegetable Pest Management
There has been a lot of effort in sustainable agriculture to expand the range of cover crops used by farmers. Information about how cover crops affect pest and beneficial insects has been pretty scant, however, especially in the Northeast. Some important vegetable pests (tarnished plant bug, potato leafhopper, aster leafhopper) are generalist insects, known to feed on many field crops or cover crops.
This project has primarily studied cover crop growth, weed suppression, and the numbers of beneficial and pest insects above ground on cover crops. We originally planned more work on wireworms and bacteria, but those aspects of the project have not gone as well as we hoped.
- 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.
Evaluate the growth and survaival of wireowrms 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 crover crops on diversity of plant-growth-promoting bacterial anddeleterious 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.
- Winter and spring cover crops tested:
Fall planted: crimson clover, rye, rye + vetch, wheat, oats, rape (fall 2001)
Spring planted (into oat residue from previous fall): annual ryegrass, oats, oats + field peas, rape (spring 2001)
Site: Lockwood Farm (Hamden, CT)is in USDA zone 6b (average annual minimum temperature 0 to –5 degrees F.) The minimum winter temperatures varied strongly from year to year, resulting in variation in cover crop survival and growth (especially oats and crimson clover).
During the winter of 2000-2001, we had one brief cold spell in January, when the temperature went down to –3. In that year, oats grew well in the fall and winter-killed, leaving a mulch that suppressed early spring weeds, and crimson clover grew moderately well, with 60% clover ground coverage and 14% weed coverage in May.
The winter of 2001-2002, the lowest temperature was 11 degrees F. Oats did not winter-kill, and kept re-growing after we mowed it in the spring. Crimson clover grew vigorously with high ground coverage and the highest biomass (both fresh weight and dry weight) of all the cover crops.
During the winter of 2002-2003, we had several cold spells below 0 (min. temperature –5) and lots of snow and rain. The oats did not grow well, winter-killed early, and no residue was visible in the spring. Crimson clover mostly survived, but did not grow as vigorously, with 46% clover ground cover and 34% weed cover. Crimson clover had less biomass than rye/vetch, rye, or wheat.
Major weeds in the May samples: chickweed, Arabidopsis, campion, horseweed, red clover
Impacts and Contributions/Outcomes
- Winter rye alone has low levels of generalist pests (tarnished plant bug, potato leafhopper, aster leafhopper), but also tends to have low levels of beneficial insects.
Winter rye plus hairy vetch has high levels of tarnished plant bug and potato leafhopper, but also has high levels of wasps and other beneficials.
In addition to rye + vetch, several other treatments have high numbers of tarnished plant bug adults (and later in the season, nymphs): rape, crimson clover, and weeds (no cover crop planted.
Although rye + vetch was the most attractive crop to potato leafhopper adults, they did not come in until after the beginning of June. Thus, for rye +vetch covers killed in a timely way, attractiveness to potato leafhopper may not be important in most years. (They don’t overwinter here and are brought up by wind patterns from the south.)
Tarnished plant bugs overwinter here as adults and thus were found even in the earliest samples in April. They tend to move to crops in the order they flower and set seed. Thus, rape and undisturbed weeds had higher numbers early (Arabidopsis, one of our major weeds, flowers in April, as does rape), crimson clover in late April to May, and rye + vetch in late May – June.
Connecticut Agricultural Experiment Station