Bill Cissel, Extension Agent – Integrated Pest Management; email@example.com
Corn earworm pheromone trap catches have recently increased throughout the state and we are starting to find low levels of larvae in full season and double crop soybean fields. Currently, populations remain low in most fields, however, there is a potential for hot spots to occur. The only way to know what is happening in a particular field is to scout it.
The most accurate way to make a treatment decision is to use the Corn Earworm Calculator developed at Virginia Tech. This tool takes into consideration the sampling method, control cost, soybean price, and row width to generate an economic threshold.
Here is a link to the Corn Earworm Calculator: http://webipm.ento.vt.edu/cew/
Corn earworms use corn as a nursery crop before moving on to other crops such as soybeans. Virginia Tech has documented a linear correlation between the level of infestation in field corn and the amount of soybean acreage that is treated with an insecticide based on over 30 years of data. Annually, Virginia Tech conducts a survey of field corn in mid to late July to estimate infestation levels which can then be used to predict the risk of corn earworm infestations in soybeans. Since most of the moths that move into our soybean fields to lay eggs migrate from the South, the level of pressure observed in the south might provide some insight on what our risk is. Here is a link to Virginia Tech’s 2017 Corn Earworm Survey: http://blogs.ext.vt.edu/ag-pest-advisory/files/2017/08/CEW_survey_results_2017.pdf
Pyrethroids have provided poor control of corn earworms in states to our south and based on vial tests conducted in Virginia, an average of 39% of the moths tested survived after being exposed to cypermethrin for 24 hours. We have not seen the decrease in efficacy to pyrethroids that has been documented in the south but it is important to remember that many of our moths moving into soybeans are migrating from the south. Coragen, Steward EC, Besiege, Radiant, and Blackhawk are all labeled for corn earworm control in soybeans. If using a pyrethroid, make sure you are using the highest labeled rate.
Here is a link to our Soybean Insect Control Recommendations: http://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063934/Insect-Control-in-Soybeans-2017-final.pdf