In 2008 you will have bugs in your beans. At this time it is too early to tell which ones, and it is too early to determine whether they will create damage that surpasses an economic threshold for a rescue treatment. But you will have bugs in your beans, so do you think now about how to respond or do you wait until your yield begins to fade?

In the 40 years prior to 2000, insect outbreaks that threatened soybeans were few an far between. Certainly memorable is the drought year of 1988 that brought two spotted spider mites to your attention. But for the most part there were few problems, and even then they were quite isolated. And during the latter years of that era, most producers learned that a spray should be something in response to a problem, not something that was applied to prevent a problem.

Since then, soybean entomology has become a dynamic discipline. You have heard about insects transmitting diseases, a new soybean aphid was discovered, and new insecticides have been developed that have changed your perspectives. University of Illinois entomologist Kevin Steffey says those may have focused your attention, but they have not necessarily lead to higher soybean yields. However, commercial product suppliers have caused producers to think that spending money on preventative products will result in improved yields. As you might expect, Steffey is not big on that philosophy. He warns against unintended consequences of pest resistance resulting from overuse of crop protectants, when you opt for the short term cost/benefit ratio that might be easily calculated.

While it may only take 1-2 bushels per acre of higher yield to pay for a pesticide or fungicide, Steffey says the entire cost of soybean production is increasing for 2008 and will cost you in the vicinity of $220 per acre, not counting land costs. That might put beans above $8 to breakeven, so spending more money on production costs will put them even higher.

But he’s concerned about the development of resistance, such as:
1) Putting a neonicotinoid treatment on soybean seeds may control an insect, but continued use will result in resistance development.
2) Controlling weeds with glyphosate is convenient, but it has an undesirable fungicidal impact on some insects.
3) Insecticide sprays may be used to control threats from insects, but repeated use creates resistance problems.
4) Use of fungicides to control a soybean disease is reasonable, but it may also kill a pathogen that had been suppressing the populations of other insects.

Insect management guidelines are a work in progress, particularly with increasing soybean yields and higher soybean values that have changed the dynamics of determining when a treatment should be used based on leaf defoliation. That has changed from amount of loss to the amount of leaf that remains to intercept light. But there are no decision aids yet to make that estimation.

In the near future, soybean resistance to insects will play a significant role in maximizing yield. This is particularly true for beans resistant to soybean aphids. Steffey says several varieties have been developed and should soon be commercialized. Another variety will have a Bt gene that makes soybeans resistant to Lepidoptera insects, but Steffey says that has not been a treat to Midwestern soybeans.

Generally, recent pests have been bean leaf beetles, Japanese beetles, soybean aphids, and spider mites, but there may be a shift occurring that some of those will recede in importance and new insects, such as the whitefly will come to prominence. So far, the species that have been seen have not caused economic damage. But Steffey says other species found in the South may cause damage in the Midwest as they have in southern states. And he says the recurrence of old pests or emergence of new pests may happen if good management principles are disregarded.

Summary:
Soybean producers should carefully consider the use of any crop protectant in an effort to reduce the potential for development of insect resistance. Preventative sprays are the first to reconsider, particularly since soybean production costs are already high. The use of leaf defoliation as an threshold for spray is changing along with higher yields and higher values, and new decision aids have not yet been developed and tested. New pests may appear at anytime, and old pests may recur, particularly if they become resistant to the overuse of chemical protectants.