CORN Newsletter: 2009-28, August 24, 2009

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C.O.R.N Newsletter 2009-28
August 24, 2009 - August 31, 2009

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Late Season Insect Concerns in Soybean
by Ron Hammond, Andy Michel, Bruce Eisley


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As we are getting into the later growth stages of soybeans, we are being asked about two situations, soybean aphids on late R5-R6 growth-stage soybeans and bean leaf beetle pod feeding. Aphid populations nearing or reaching the threshold level of an average of 250 aphids per plant during growth stages late R5-R6 is a unique concern because as of yet, researchers have not been able to establish an economic injury level (EIL). We believe that it is higher than the EIL during the R2-early R5 stages (700-800 aphids per plant). Thus, the action or economic threshold should probably be higher than the 250 aphids per plant that is for the R2-early R5 stages. Additionally, we assume that plants in the late R5-R6 stages are probably not as good of host plants compared with earlier growth stage plants. Thus, we are not sure of the potential for the aphid population to go much higher. Related to that is the time from those stages until the plants begin to mature. We would suggest that prior to making any decision to spray, that growers sample multiple times over a number of days to make sure that the level is indeed rising well above the current threshold of an average of 250 aphids per plant. As discussed, how much higher the population should get to in order to spray is not currently known. Leaving unsprayed check strips and reporting any results to your county Extension Educator would help us determine whether economic damage is actually occurring at the late R5-R6 growth stages.

On the other hand, bean leaf beetles are an annual concern in soybeans in late pod development stages, especially in late maturing soybeans, which will remain green well into September. These fields can often have higher levels of pod feeding because the fields act as trap crops for second-generation bean leaf beetles, providing a food source prior to overwintering. Fields could include those that were late planted, double-cropped soybeans, and relay-intercropped soybeans. Although bean leaf beetles have not been extremely high this year, we still felt it important to caution growers of potential pod feeding. Growers are advised to continue monitoring these fields until they begin to mature in mid to late September. Although leaf defoliation will not be a major concern, injury to the pod is a problem because of yield loss potential and seed quality issues. Of note, this concern is especially important with food grade soybeans and soybeans being grown for seed. If bean leaf beetle populations are high, insects are still active, and pod injury has reached 10% and is relatively new, an insecticide treatment is perhaps warranted to prevent further pod injury.

For any insect pest, growers should be careful with any insecticide used during the later growth stages because of the shorter time period from application to harvest, the PHI or pre-harvest interval. See the Agronomic Crops Insects website on insecticide information provided in Bulletin 545 (http://ohioline.osu.edu/b545/pdf/b545.pdf) that lists the PHI for all labeled insecticides.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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