Crop Insurance Today May 2012 - (Page 28)
Insect Resistance to Bt
Is it a new threat to corn production?
es, such as the ALS and ACCase classes, as well as insecticides. The corn root worm group, made up of the three most common root worm species: the western corn root worm (Diabrotica virgifera virgifera LeConte), Southern (Diabrotica undecimpunctata howardi Barber), and Northern (Diabrotica barberi Smith and Lawrence) have been considered the major pests for corn since the 1950s. Farmers used various cultural controls, such as yearly crop rotations, to help control these insects. In areas where farmers did not switch crops each year or had continuous corn, different chemical classes of compounds, such as chlorinated hydrocarbons in the 1950s and 60s, were used to control these pests, and later organophosphates and carbamates in the 1960s through today. The advent of incorporating Bacillus thuringiensis (Bt) for control of the corn root worm seemed to provide a safer way to get control of these insects and provide for a smaller impact on the environment. Humans, of course, keep forgetting that nature has a way of messing with our well made plans. Two examples are the northern and western corn root worms. The northern rootworm was the first species to develop a mechanism to avoid the control provided by yearly crop rotation. The northern root worm was able to develop a prolonged diapause, or resting stage for it’s eggs, after the eggs were deposited in corn fields in the fall. These fields would most often be seeded to soybeans the next year, which does not provide a food source for the developing larva. This prolonged diapause ensures that the larvae will hatch from eggs into a field of corn and thus be able to grow instead of dying off when trying to feed on soybean roots. The western rootworm developed a different strategy in that it would seek out and lay the eggs in fields of soybeans so that, when the fields were rotated to corn the next year, the developing larvae would have corn roots to feed on. Both of these are amazing ways that nature and insects have been able to change their normal responses to be able to survive the yearly rotation of crops. “Problem fields”—fields that had unacceptable damage due to western corn root worm feeding were reported in Iowa and Illinois in 2009 and 2010. Crops there were sown with Bt corn hybrids with the protein Cry3Bb1 incorporated into these plants. These hybrids were sold under the name YieldGard (c) and could be found in hybrids that had the corn rootworm control alone, or stacked with herbicide
By Dr. Mark Zarnstorff, NCIS
Crop production has many roadblocks to efficient production including: weather, availability of inputs (fertilizers, ag chemicals), weeds, disease and insects. Science has continually played a role in overcoming some of these concerns—especially the weeds, disease, and insects. The problem is that nature has a way of adapting and becoming resistant to the methods used to combat these problems. Over 90 million acres of corn were planted in the U.S. in 2011. Because of its “popularity,” scientists and farmers have worked hard for many years to develop ways to overcome the hurdles of weeds, disease, and insects. There are various chemicals for weed control but some are no longer effective because they have been overused and weeds have become resistant. An early example from the 1980s is atrazine resistant weeds. The most recent is Roundup®. Weeds that have shown resistance to it include: Horseweed (marestail), Common ragweed, Palmer Amaranth, and Waterhemp. There are other problems with other herbicide class28
The bottom line is that without the proper use and rotation of the different sites of action or chemistries available, we are pushing the time that these technologies can be effective.
Table of Contents for the Digital Edition of Crop Insurance Today May 2012
Commitment to Excellence
2011 Year in Review
Farming: Pessimists Need Not Apply
Leadership: NCIS Regional/State Crop Insurance Committees
NCIS Board of Directors
Insect Resistance to Bt: Is it a new threat to crop production?
Another Successful Convention
Adam Vetter Given Outstanding Service Award
Pat Flanagan Given Industry Leadership Award
Step 6-Identifying and Evaluating Alternatives: What alternatives are feasible for the future?
In Memory of John F. Ames
Crop Insurance Today May 2012