GOODING • Livestock feed and improved soil health are two reasons why growers across southern Idaho are planting more cover crops. But another reason is starting to emerge.
By selecting specific species, growers can manage nematode and insect populations that plague cash crops. There is even some evidence that cover crops may even help control voles.
Cover crops seem best suited to managing nematode populations in the soil, Carlo Moreno told growers at a cover crop meeting sponsored by the Gooding Soil Conservation District and University of Idaho Extension.
Cereal cyst nematode is becoming a large problem in Minidoka County, where Moreno is the UI Extension educator. Researchers with UI, Oregon State University and Washington State University estimate cereal cyst nematode reduces wheat profitability in the Pacific Northwest by at least $3.5 million annually.
Nematodes are tiny but complex unsegmented roundworms. Many species are beneficial to agriculture particularly when breaking down organic matter. But some, like the cereal cyst and sugar beet cyst nematode, are parasitic to crops.
These nematodes invade the roots of cash crops and cause swelling in the roots that make it difficult for the plant to uptake water and nutrients. Patches with stunted or chlorotic plants distributed unevenly across a grain field may be a sign that cereal cyst nematodes are present.
“(Crop) rotation is a key but nematodes also attack the crops you rotate to,” Moreno said.
Some cover crops, such as oilseed radish or white mustard, trap juvenile nematodes in plant tissues and leave them vulnerable to pesticide applications or winter injury. Although these species are proven to be highly effective, the seed is hard to find and is very expensive, Moreno said.
Sunn hemp is a warm season legume that produces fantastic fodder for livestock and is also a terrible host for nematodes. Just the presence of sunn hemp is enough to dissuade some nematodes from living in the field.
Brassicas and sorghum-sudangrass can be grown as biofumigants. These crops need to be planted at least six weeks before the juvenile nematode populations peak (generally late spring), Moreno said. The cover crop should be mowed at least two weeks before flowering to minimize volunteer plants and incorporated immediately after mowing to incorporate the resulting gasses that kill nematodes.
Using cover crops to manage insect pests is similar to that of controlling nematodes.
Rye, triticale, millet or sorghum-sudangrass are all good species for trapping insects. Planting a border around a winter grain field with one of those species may serve as a barrier to aphids that don’t fly well. Aphids are often carried on the wind from corn fields to newly emerging winter grain fields so planting a border may block some and reduce the incidence of barley yellow dwarf virus, a disease carried by aphids.
Red clover has also been shown to be very effective for controlling aphids and some wireworms. Moreno has seen some farmers in developing countries plant corn directly into red clover.
Leaving grain stubble or using no-till seeding can promote habitat for beneficial insects such as wolf spiders, ground beetles and staphylmid beetles that will then feed on insect pests. Flowering plants along borders may also help attract beneficial insects, Moreno said.
While Moreno can see clear benefits of using cover crops for nematode or insect control and is working with farmers to implement these practices; he is less convinced that cover crops can control voles. Indeed, UI extension educators have seen voles wipe out several cover crop demonstration plots around the Magic Valley.
Still, Moreno is working with an organic grower who plants a cover crop border around his barley fields, and then baits the border. He does not count the border in his organic acres and does not harvest the border so he does not impact his organic certification.
Other growers have tried planting a crop that voles don’t like between the rows of the desired crop; while others have tried compacting the soil or tilling frequently around the perimeter of a field to discourage voles from entering a field.
Using cover crops to control pests is complicated, Moreno said. In many cases, pesticides are cheaper. But if a grower can get other benefits from the cover crop — such as extra livestock feed or a boost in soil organic matter — than some additional pest control may be a nice bonus.