With the higher prices you have booked for 2008 corn and soybeans, what will be the basis for your decision on any type of pestilence that might arise this year? You might have Asian rust decimating soybean leaves. You might have Japanese beetles eating your corn silks. And if you know what your price risk is, does that increase or decrease your threshold level for a rescue treatment. Let’s recalibrate your sights as you aim at the bug in the bull’s eye.

Entomologists Mike Gray and Kevin Steffey at the University of Illinois have offered a couple thoughts that may help you profitably adjust your plans to cultivate and protect a truly valuable crop. In their latest newsletter Gray and Steffey consider when a rescue treatment is “needed.” Usually the answer has to do with economics, and whether there will be a return on the investment made in the insecticide or will the value of the yield offset the cost of the control. You have probably used those concepts in the past to determine when it is time to climb on the sprayer.

The specialists say, “In simple terms, the economic injury level is the point (of injury or insects) at which the value of expected crop loss equals the cost of control.” There is no rocket science here, but one issue that needs some clarification is the threshold or insect population density which causes you to pull the trigger. They quote a theory that “the economic injury level equals the cost of control, divided by the market value of the crop, the injury units per insect, the damage per injury unit, and the proportional reduction in insect injury.

While you are wondering what numbers to plug into that formula, Gray and Steffey say, “The question of whether economic thresholds for making insect control decisions will be lower in 2008 refers directly to the market value of the crop. Most people know that as the value of the crop increases, economic thresholds decrease.” In other words, if you pulled the trigger when four Japanese beetles were found eating the silk on $2.50 corn, you will be spraying a field of $5 corn much quicker. But is the number two beetles or three beetles?

Gray and Steffey share your lament that the answer does not come easy. Just because the price of soybeans has doubled from $6 to $12, that does not mean it only takes half the number of soybean aphids to warrant a rescue treatment. In their terms, “the relationship is not linear.” The entomologists admit they do not have an exact formula for economic thresholds that will accommodate the new commodity prices; and they say lowering the range is not a light decision, but will take several years to confirm. And to complicate the calculation will be changes in yield, plant populations, and input costs, all of which necessitate further adjustment.

The entire concept of calculating economic thresholds is designed to manage crop production with the greatest intelligence and management of risk. That applies also to managing your corn rootworm, corn borer, and weed problem, with the use of triple stacked genetic hybrids. While the bag of seed is higher in cost, the corn at the end of the year has a higher value this year. A recent Gray and Steffey commentary on Bt hybrids underscores the need for the prescribed refuges on 20% of adjacent acreage despite the temptation to plant all of your corn acreage to the premium seed. The threat to the viability of the Bt genetics is increased by the absence of the refuge, but the viability of the Bt hybrids is retained with a refuge. Two outcomes that are possible with the lack of prescribed refuges are regulations and the lack of efficacy in the Bt hybrid in controlling corn rootworm and corn borers. The loss of effectiveness will result in increased production costs and reduced profitability in future years.

Summary:
The higher prices you will be getting for corn and soybeans this year mean the crop is more valuable per acre, and with the higher value is a lower threshold for applying a rescue treatment in the event of pestilence. But the question is, what is that new threshold? Entomologists say just because the value of your corn and beans is twice as much, does not mean the threshold is cut in half. 2008 economic threshold ranges will be less than prior years, but the exact parameters will need research and testing.