A typical leaf symptom of BPMV is a yellow and green blotchy appearance called leaf mottle.
Photo credit: Palle Pedersen.
Click on image to view larger version.
UW Soybean Plant Health
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Symptoms of early feeding by bean leaf beetles. Click on photo to view larger version. Photo credit: Craig Grau |
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Adult beetles overwinter under leaf debris near soybean fields. Once they become active in the spring they will feed on wild legumes, alfalfa and clover. Once soybeans begin to emerge, the beetles quickly leave these alternate hosts and concentrate on soybean.
Treatment thresholds, for defoliation only, varies according to crop value and treatment cost. For VC to V2 soybeans the threshold varies between 2 to 10 beetles per plant. Treatment thresholds for prevention of bean pod mottle virus are not yet available.
Second generation beetles
The overwintered bean leaf beetle population will give rise to another round of first generation adults who in turn lay their eggs in the soil. These larvae give rise to second generation adults that can be found in soybean from late-August to mid-September where they feed on leaves and pods. This describes a two generation per year bean leaf beetle, and this is probably what we have in southern Wisconsin.
Bean leaf beetles and soybean viruses
In addition to the physical damage from feeding on soybean, the bean leaf beetle is also a vector of bean pod mottle virus (BPMV). The insect feeds on infected plants and transmits the virus particles to the next plant on which it feeds. Virus transmission can occur at any growth stage, however early infection poses the greatest risk of yield loss.
A typical leaf symptom of BPMV is a yellow and green blotchy appearance called leaf mottle. Young leaves show symptoms more severely than older leaves, and symptoms are most obvious during periods of rapid growth and cool temperatures. BPMV can also cause green stem and seed mottle.
Read more about BPMV»
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Early soybean planting often attracts high beetle populations and increases the chance transmitting BPMV. Concentrate initial scouting activities in early-planted fields. Treatment thresholds for prevention of bean pod mottle virus are not available. However, consider these criteria before treating:
- Were yields last year lower than expected and unexplainable? Were virus symptoms (leaf mottling, discolored seed, green stem) present ? If so, then BPMV is likely a concern for the coming season.
- Soybean varieties differ in susceptibility to BPMV. If a variety was planted last year which had significant bean leaf beetle feeding yet few, if any, virus symptoms, that same variety may be considered (somewhat) tolerant to BPMV.
- Synthetic pyrethroid insecticides tend to provide the most consistent bean leaf beetle control.
- To prevent transmission of BPMV, an insecticide application must be made in the very early stages (V-V2) of soybean development.
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A second application may be necessary during the emergence of first generation beetles (late June or early July).
Colors and spot patterns of bean leaf beetles can range considerably. Therefore, careful attention is needed to distinguish these beetles from other important beetles found in soybean, such as the lady beetle.
Photo credit: UW Entomology
Read more on beetle identification (link to ISU newsletter)» - Delayed spraying at either crop stage can seriously increase incidence of BPMV.
- Early soybean planting often coincides with high populations of overwintered bean leaf beetle adults moving into soybeans to feed and lay eggs. This increases the chance of BPMV transmission to soybean.
Questions? Please contact Eileen Cullen (cullen@entomology.wisc.edu), Department of Entomology.
Information from this site can be copied and distributed for educational use. Please credit the source with our name and URL: University of Wisconsin-Madison, Departments of Agronomy, Entomology, and Plant Pathology at www.plantpath.wisc.edu/soyhealth.
11/08