Plant Health Initiative

Bean Leaf Beetle - Management

Second generation bean leaf beetles feeding on pods. Feeding at this growth stage can cause loss of yield and seed quality. Photo credit: Michael A. Catangui, South Dakota State University Click on image to view larger version.

Sampling for beetle thresholds
Researchers at Iowa State University have developed a research-based management concept based on sampling the first generation of beetles to predict the size of the second generation. Feeding by the second generation beetle at the beginning of pod growth and development has the greatest potential for yield and quality loss in the crop..

If first generation numbers reach densities that indicate the second generation may cause economic losses, treatments are made in August as soon as the second-generation beetles are found. This prevents the situation of the second generation beetles feeding for several weeks before economic levels are reached.

The model is based on degree days and is described in detail in the following article:
Predicting first-generation bean leaf beetles
Integrated Crop Management Newsletter, Iowa State University.

Early-season management decisions for management of just the beetle, or for beetle and virus interactions, are outlined in the following two articles:

Bean leaf beetle and bean pod mottle virus management: An integrated approach. Integrated Crop Management Newsletter (2005 - but still current),

Revisiting an integrated approach to bean leaf beetle and bean pod mottle virus management
Integrated Crop Management Newsletter (2007 - but still currrent).

 

Soybean varieties

Soybean varieties differ in their maturity rate and may be more or less susceptible to bean leaf beetle feeding. An early-maturing variety may be susceptible to late first generation pod feeding while another may set pods after first generation activity has peaked. Similarly, a late-maturing variety may be more vulnerable to bean leaf beetle injury when the second generation peaks in the late summer or early fall.

Early planting can impact beetle populations

The relative proportion of soybeans planted early in an area may have a significant impact on the establishment and development of bean leaf beetle populations. Fields planted earliest in an area are most at risk for high populations of the beetle. First-generation populations are limited in late-planted soybeans if the stand emerges after the overwintering adults have concluded egg-laying.

Managing beetles for virus control

A separate issue with bean leaf beetles is the physiological stress caused by  transmission of the bean pod mottle virus (BPMV). Although bean leaf beetles transmit BPMV all season long, soybeans are most affected when plants are infected in the seedling stage. 

Researchers at Iowa State University have constructed a flowchart to help growers with insect/virus management decisions. The flowchart is a dynamic, two-pronged decision guide based on field history. If bean pod mottle virus has not been present in a soybean field, then the only reason to consider early-season bean leaf beetle management is if populations reach extremely high levels  (more than 2.5 beetles per plant). Insecticide treatment will not be cost-effective if the virus is not present.
 View flowchart (pdf)»

Right now, most of the information for predicting economically important variables for beetle damage is available. Much more information is still needed regarding these variables and bean pod mottle virus. As more research is conducted, the results can be added to the decision guide.

View the entire article at:
Revisiting an integrated approach to bean leaf beetle and bean pod mottle virus management
ISU Integrated Crop Management Newsletter