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Published July 14, 2014, 09:16 AM

Bare soil kills pests and friendly insects

Cover crops are all the rage these days, and might be a part of the solution for problems confronting the long-term sustainability of agricultural production in the U.S.

By: Jonathan Lundgren, Agweek

Cover crops are all the rage these days, and might be a part of the solution for problems confronting the long-term sustainability of agricultural production in the U.S.

Simply defined, cover crops are plant “place-holders,” designed to cover bare soil during fallow periods and between growing seasons. Their benefits are many, from reducing soil erosion, to replenishing soil nutrients, to suppressing weeds, to growing soil microbial communities. Arguably the most important benefit is in reducing pest insects and growing beneficial insect communities.

Bare soil kills a lot of insects. Actually, bare soil kills most biology in a system. For this reason, farmers and entomologists alike have long touted that a good way to remove pests from a farm or garden is to till it and get rid of any noncrop vegetation. But the problem is that you remove all of the friendly insects from the system, as well. Predators (lady beetles, ants, spiders, ground beetles, lacewings, pirate bugs, etc.), pollinators and detritivores are also driven off the farm. And farms need these beneficial insects to function properly.

Then the farmer comes back in the spring and plants entire fields of a single plant species, the first to arrive is the pest. And there is no biotic resistance to the pest’s proliferation because all of the predators that keep those pests in check have been driven out of the system, too. So the farmer sprays insecticides to replace the predation that Mother Nature normally gives for free and further drives down the natural enemy communities, while temporarily suppressing the pests.

An alternative is to provide habitat for natural enemy communities, so they are there when the pests arrive in the spring. And cover crops are a great way to do this.

Research at the U.S. Department of Agriculture Agricultural Research Service laboratory in Brookings, S.D., has shown that cover crops preceding corn or soybean can have dramatic effects on natural enemy communities, sometimes increasing predator numbers by 10 times those found in insecticide-sprayed fields; these predators eat things such as corn rootworms and soybean aphids.

This research shows that cover crops preceding corn (and their associated predators) reduce the abundance of corn rootworms and the damage they cause to corn plants. Now we are testing whether cover crops could be economically competitive with “traits-based management” (Bt corn, neonicotinoid seed treatments, etc.) on farms throughout the plains region.

But like any technology, cover crops need to be used correctly. Simply replacing one monoculture cash crop with a monoculture cover crop has been shown to foster pest populations such as pea weevils and armyworms. The science is still rolling in, but it seems that diversifying the cover crop mix to include several plant species might help overcome these unique and infrequent pest problems.

Using plant diversity to foster natural processes — especially those that foster soil health and biology — seems like a good alternative to constantly fighting for control against natural systems.

Cover crops could dramatically reduce farming input costs for things such as pesticides. Now we need to get the science involved to make it as easy as possible for interested landowners and gardeners to implement these tools with predictable success.

Editor’s note: Lundgren is a research entomologist with USDA in Brookings, S.D.

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