Corn lodging caused by larval rootworm feeding. Image credit:University of Illinois
Too much of a good thing often brings an unexpected crash and very painful results. America put Elms on every street and within a generation Dutch Elm Disease killed every elm on every street and every park. Treeless public spaces were sad and ugly.
For decades we spritzed DDT on nearly everything - sheep, cows, pigs, humans, yards, campgrounds, entire suburbs even - and then, shockingly, DDT stopped working on the bugs we most wanted to kill: mosquitoes. There are many more examples: parking lots and rooftops sprawling everywhere increased the likelihood of flood damage; too much coal and oil burning is currently creating a Venus-like atmosphere.
Have you heard the latest example? Continuous use of a particular variety of Bt corn - a singular "Cry" form of the pesticidal protein in Bt corn - has led to documented examples of resistance in the western corn root worm. The examples are from two of the most productive corn states and thus are a very big deal.
Before Bt corn.
The western root worm commonly chewed the corn root tendrils right where they enter the soil surface. Corn yield would fall; and right before harvest a stiff wind could more easily blow the plants down making it worse. This blow down effect is sometimes called "lodging," as pictured. (Lodging can also describe broken stalks.)
After Bt corn became the predominant seed type used.
By inserting a gene segment used by a Bt-making bacterium into corn, corn plant roots 'naturally' contain residues of one or more Bt proteins toxic to the root borer. Borer's chew and then they die. At least in the beginning, farmers who used the Bt corn found their average yield went up and pesticide application costs went down. Every farm agent recommended it. Soon it was only those loony organic growers who went without.
Before we get to the root of the matter, look how important Iowa and Illinois are for US corn production.
I thought the map made it easier to appreciate how big a deal this is.
All the planets lined up for Bt resistance.
As I pointed out in Where Did "More" Corn Ethanol Really Come From? There was never any 'empty' prime farmland on which to produce the increasingly large crop of Federally subsidized ethanol-corn..."the simultaneous net expansion of corn and soybean acreage resulted from a reduction in cotton acreage, a shift from uncultivated hay to cropland, and the expansion of double cropping (consecutively producing two crops of either like or unlike commodities on the same land within the same year)."
Continuous exposure to Bt on a large portion of all prime US farm land has created Bt resistance in corn borers. Examples cited below are from Aces News, Severe root damage to Bt corn confirmed in northwestern Illinois
This particular form of Bt resistance was first found in Iowa.
Earlier this month Aaron Gassman of Iowa State University confirmed field-evolved resistance by western corn rootworm to the Cry3Bb1 protein in an Iowa study.And then later it was confirmed in Illinois.
Severe root damage observed in Bt corn in northwestern Illinois last week should alert growers to carefully consider 2012 seed selection choices, said Mike Gray, University of Illinois Extension entomologist.Tips on how to respond to the resistance contain a certain measure of doubling down.
Consider a long-term integrated approach to corn rootworm management that includes multiple tactics, such as adult suppression programs, use of soil insecticides at planting, rotation of Bt hybrids that express different Cry proteins, and rotation to non-host crops.Even if ethanol subsidies go away, it seems possible that Bt resistance may eventually encompass other Cry protein variants, given the increased demand for US grown corn by China and given the pressure to increase the cash receipts from US grain exports, helping out the balance of trade.
Griping by environmentalists will not be what causes Bt corn to lose traction in the market place (although the right wing think tanks will blame them for decades). Farmers will be the ones. They're the ones who bought Bt hook line and sinker and they're the ones who will have to decide how to manage their own land.