Fighting Corn Rootworm Naturally
Corn rootworm (CRW) is a common corn insect that costs producers about $1 billion dollars a year in lost yields. CRW started to thrive after World War II for several reasons. First, farms got bigger and the crop rotation got simpler. Larger equipment and more corn on corn or a simple rotation of corn and beans led to poor soil health. Predators to CRW like to live in healthy soils with many cracks and pores and live roots so they can move around. Tillage and compaction increased the prevalence of CRW.
Here are six natural ways to fight corn rootworm (CRW). First, minimize tillage and soil disturbance. CRW do not thrive in undisturbed soils because of all the roots, microbial diversity, and insect diversity. CRW are prey to numerous viruses, bacteria, protozoa, and fungi, with 10 billion microbes representing over 11,000 species in just one teaspoon of soil. The most current estimate is that there are a quintrillion insects on planet earth. A quintrillion is a billion billion, or a 1 followed by 18 zeros. Other larger macro fauna like nematodes, worms, and arthropods like centipedes, millipedes, springtail, mites, spiders, and other small vertebrates consume CRW.
A second way is to minimize using broad spectrum insecticides. Why? Because they are deadly to all the predators of CRW. For example, Dr. Dwayne Beck got in trouble for advocating zero insecticide use at the research station he was in charge of in North Dakota. He was using no-till, cover crops every year, and zero insecticides in an area known for high CRW and had little to no corn damage. Researchers doubted him, so they planted 100 CRW eggs every foot to test his claims. After 6 weeks, they found zero CRW. Why? Upon further study they found a billion predators who may or may not like eating CRW, but when you are hungry, they eat everything in sight. If you have been doing a lot of tillage and using insecticides, it might take 3–5, even 7 years to restore that kind of diversity back in your system.
The third way to increase beneficial prey to CRW is to increase plant diversity. That means adding more roots and adding cover crops. Cover crops supply the habitat (food, shelter, moisture, pore space) for CRW predators to thrive. Lots of roots improve crop residue and pore space for these critters to move around to find their prey. Lots of different plant roots give many different microbes, insects, arthropods, and small vertebrates a place to thrive.
A fourth and fifth way is to keep the soil covered not only in crop residue but also in living plants. It is not only plant diversity and root diversity; it is the density of roots and shelter and the length of time that soil is covered with live plants and crop residue. A healthy soil should be covered with live plants and live roots year-round and buzzing with insects, worms, and other beneficials. Keeping the soil covered keeps the soil warmer in the winter and much cooler in the summer. Corn thrives in the summer under these conditions and has less stress. CRW love to attack crops that are under high stress. In a hot dry summer, soil temps may be 20–40 degrees cooler with cover crops and residue compared to bare soil and will hold more moisture.
A sixth way to hurt CRW is to make the CRW’s life more complicated. Increase crop rotations by adding more crops, perhaps a perennial like hay or wheat. CRW thrives when the crop rotation is short (corn–soybean) or especially corn after corn. The western CRW has even adapted to laying its eggs in adjacent soybean fields so that it can attack the corn rotated to those fields. CRW are insects that have adapted to simple rotations, simple continuous use of certain insecticides, poor soil structure (few predators with a lack of pore space), and few weeds or other root systems (a lack of diversity). CRW can easily adapt and thrive under our simple agriculture system (tillage, insecticides, herbicides, simple crop rotation).
When you add no-till and use cover crops to get more plant and root diversity, the microbial diversity increases along with insect diversity. If you can increase the crop rotation and minimize the use of broad-spectrum insecticides, you get more diversity and increase the CRW complexity to deal with these issues. If you can get 1 billion CRW predators per acre, you will have few if any insect issues because the system is in balance. Adapted from a STRIP Tillage article by Noah Newman and Ann Marie Journey.