Now that soybean harvest is well under way throughout the state, this article is a tad bit late as a "warning." However, while reading an article that Marlin Rice wrote in the September 23, 2002, issue of Iowa State University's Integrated Crop Management, I decided better late than never.|
Bean leaf beetles and western corn rootworm adults gave soybean growers fits in large areas of northern and central Illinois during August and September this year. Many growers had insecticides applied to their soybean fields to prevent excessive pod feeding and peduncle clipping (causing pods to fall off) as well as to alleviate some concern (much of it unfounded) about insect transmission of soybean disease pathogens. We are not certain how many acres of soybeans were sprayed with insecticides, but reports into our office suggest that acres treated in 2002 were "more than average." Whether all of these insecticide applications were justified is debatable and is not the focus of this article. It's more important for people to know about preharvest intervals for the insecticides that were applied to soybeans (i.e., the legal number of days between insecticide application and harvest).
Although several insecticides are labeled for control of bean leaf beetles in soybeans, not all of them should be used against the second generation of beetles that occurs in late summer. Table 1 shows the preharvest intervals and related remarks for several insecticides labeled for use on soybeans. Some of these products (e.g., Ambush, Pounce, Warrior) have very long preharvest intervals (e.g., 45 to 60 days). Other products have relatively shorter preharvest intervals (e.g., 20 to 28 days). Obviously, products with long preharvest intervals probably should not be used to control bean leaf beetles or other insects causing injury to soybeans late in the growing season.
So what are the consequences if soybeans are harvested before the preharvest interval of a specific insecticide has elapsed? Pure and simple: it's illegal to harvest soybeans before the preharvest interval of a specific insecticide has elapsed. And growers bear the burden for this if they do. Some select sentences from Marlin Rice's article spell it out. "The Federal Food, Drug, and Cosmetic Act, Chapter IV, Section 402 (2B) states: 'A food shall be deemed to be adulterated if it bears or contains a pesticide chemical residue that is unsafe within the meaning of section 408(a).' This means that if any pesticide chemical residue is found on the soybean that exceeds the established pesticide tolerance then it is unsafe. The farmer that hauls soybean to the grain elevator with contaminate residue would be liable for delivering to the marketplace soybean with illegal residues and any other problems they could cause. Unsafe soybean could create many problems at the grain elevator or with potential sales to international markets."
Soybeans sprayed with an insecticide should not be harvested before the preharvest interval indicated on the label. It's better to leave the soybeans in the field for a while than to flirt with the possibility of significant penalties.
Note: A program focused on bean leaf beetles and soybean diseases will be delivered via Latitude Bridge from campus to sites around the state sometime during the winter. Mike Gray, Dean Malvick, and I will direct the program from campus, and Marlin Rice (entomologist) and John Hill (virologist) will participate from Ames, Iowa. We'll announce the specifics about the program in a future issue of the Bulletin.--Kevin Steffey