The last few winters have been tough for the bean leaf beetle in Iowa. But the 2010-2011 winter was a little more forgiving and predicted overwintering survival was a higher than in recent years. The southern third of Iowa has the highest risk of bean leaf beetle adults surviving the past winter. (Click here for a mortality map produced for the Iowa State University ICM Newsletter in April.)
Now is the time to start scouting for bean leaf beetles in soybean fields. "Adult bean leaf beetles are strongly attracted to emerging soybeans and will move from protected areas into soybean fields during May and June," says Erin Hodgson, ISU Extension entomologist.
If you see beetles on beans in June, should you spray an insecticide? "Management of overwintering bean leaf beetles is generally not necessary," she answers. "Defoliation on young soybean plants may look terrible, but is usually not economically damaging. Plants will quickly outgrow the defoliation and produce new leaves. In addition, insecticide seed treatments are very effective in reducing early-season feeding. So if you planted soybean seed that was treated with an insecticide seed treatment, that should help."
Soybean seed producers concerned about bettles spreading disease
However, there is another potential problem. Bean leaf beetles carry a soybean disease called bean pod mottle virus, and the beetles spread this disease.
"Growers concerned about bean leaf beetle vectoring the soybean pod mottle virus should pay closer attention to the arrival and spread of overwintering adults," says Hodgson. "This is something seed producers are especially concerned about, since this disease affects how soybean seeds look. Maintaining seed coat quality is dependent on preventing virus transmission. Seed production fields may be sprayed if bean leaf beetles are a problem. Foliar insecticide treatments should be timed with the first arrival of adults and then sprayed again if first generation adults emerge in early July."
Scouting for bean leaf beetles is difficult because they are skittish and often fall into soil cracks when disturbed. When fields are at the soybean growth stage of VC-V4, you should carefully walk in the fields and look directly at plants. After the V5 growth stage of soybean plants, use a sweep net to capture the adults to get a count on the population that is in your field.. Determine the number of beetles per row of foot or per sweep to estimate the density."
Sulfur deficiency in corn, fungicide application and corn nematodes
Here are three other crop management topics you may be interested in that were released June 13, this past week, by ISU Extension. These are audio files provided by ISU, called "Crop Minute." New "Crop Minute" audio files about new topics are released each week. Just click on each one below, to listen to what the ISU specialist has to say about the particular topic.
* June 13, 2011 - John Sawyer, ISU Extension soil fertility specialist, discusses sulfur deficiency in corn.
* June 13, 2011 - Alison Robertson, ISU Extension plant pathologist, addresses the "talk in the field" regarding early season fungicide applications.
* June 9, 2011 - Greg Tylka, extension nematologist, discusses testing for nematodes in corn.