It's all getting done, the corn crop is well in and planting of soybeans is underway in earnest. Don't worry if you don't have all your beans in yet. Having the first soybeans up in an area is a guaranteed invitation for bean leaf beetle feeding. Feeding by bean leaf beetle poses the obvious problem of actual physical damage to the plant, but additionally we know that the beetle has the key role in transmission of bean pod mottle virus (BPMV) to the plant. There has also been significant concern that the BPMV infection was possibly related to increases in 'green stem disorder' that is so troublesome at harvest.

Well, at least one part of the soybean, bean leaf beetle, BPMV, 'green stem disorder' has been sorted out. Researchers at the University's of Illinois and Wisconsin recently published results of a multi-state, multi-location project investigating whether or not "green stem disorder" was related to or a result of BPMV infection. They found that BPMV incidence in surveyed and tested fields was often higher than the amount of 'green stem' present. Additionally, they found 'green stem disorder' developed in the absence of BPMV infection. Also, the study found that the same varieties in different locations showed varying levels of BPMV infection but similar levels of 'green stem' incidence. The researchers concluded that 'green stem disorder' is independent of BPMV infection. What does that means to a producer? It means that managing bean leaf beetle may control physical damage to a plant or affect virus infection but it won't do anything to manage 'green stem disorder'.

So now let's move on to a discussion about the virus and the beetle. Bean pod mottle virus BPMV is not a new disease to Illinois. Infection can cause losses of 10-17%. The disease primarily causes a mottling and distortion of leaves in the upper canopy of the plant during periods of rapid growth and cooler temperatures. Seeds of BPMV infected plants may have a light purplish discoloration of their seed coat. It's natural host range of concern being soybean and green bean. Several kinds of beetles can move infective sap around to spread the virus disease, the most prevalent being bean leaf beetle. Other beetles can transmit the virus including grape colaspis, striped blister beetle and several types of rootworm beetles. No commercial resistant varieties are currently available to manage the disease.

The bean leaf beetle cause direct physical damage to soybean and is also a main culprit in BPMV transmission. It comes in a lot of colors, from light green to tan, and orange to red, some have black spots on their wing covers, all however, have a black triangle right behind their head. Delays in planting and emergence of surrounding soybean fields will increase your chance of feeding damage from the beetle in your early-emerged fields. The treatment threshold for bean leaf beetle causing physical plant damage is 16 beetles per foot of row in the seedling stage that is, by the way, a considerable number of beetles.

So should you spray the beetle to reduce possibility of transmission of BPMV? Well, there is no definitive answer to this yet. Our recommendation in Illinois takes several factors into consideration to make the decision whether or not to spray. First, have you actually had BPMV in your fields before? You can only know this if you had the field tested for the virus. If you have an area where BPMV has been verified to cause significant yield loss or mottling of seed in the past, are near wooded areas, alfalfa fields, or other areas where large numbers of bean leaf beetles have been observed then spraying may be justified. Keep in mind though that even if you mange most of the bean leaf beetles infection can still come from or western corn rootworms. As we have seen with many other virus diseases, rarely is spraying for a vector that is present throughout the growing season an effective method of reducing virus disease. Bottom line; your best management tool is to not plant too early.