Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
As the potential for late season insect control increases, be sure to check all labels for the days from last application to harvest as well as other restrictions.
Continue to scout for soybean aphids. Above threshold levels have been found as close as western Virginia. There are also reports of an increase in populations in Ohio and Kentucky, so be sure to scout for this pest. In general, we continue to find low levels in fields throughout the state. We can also find isolated fields statewide with populations averaging around 40-50 aphids per plant. Although our survey efforts have been concentrated in full season soybeans, you should scout both full season and double crop soybeans for aphids. With the delayed planting this year, double crop soybeans may be more susceptible to damage since they will be in the vulnerable stage for attack if populations continue to increase, especially if the weather is cool. In some cases beneficials are present and in other cases beneficial activity is low. As a general guideline, treatment is needed through the R-5 stage (seed is 1/8 inch long in the pod of one of the four uppermost nodes on the main stem) of soybean development if economic levels are present. It may also be beneficial to spray through R-6 stage (pods containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem) — reports vary as to the benefit of spraying once plants reach the R-6 but in some years and some situations there has been an economic return. Spraying after R-6 stage has not been documented to increase yield in the Midwest. The suggested treatment threshold from the Midwest is still 250 aphids per plant with 80% of the plants infested with aphids. You can also consider using speed scouting to make a treatment decision. Information on how to use speed scouting can be founds at: http://www.nwroc.umn.edu/Cropping_issues/2007/Issue9/07_17_07_no4.htm or http://breeze.ag.vt.edu/speedscouting.
Continue to scout for stinkbugs in fields that are in the pod development and pod fill stages. Economic damage is most likely to occur during these stages. You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. We are currently following the same guidelines that are being used in Virginia. Thresholds are also based on numbers of large nymphs and adults, as those are the stages most capable of damaging pods. As a general guideline, current thresholds are set at 1 large nymph/adult (either brown or green stinkbug) per row foot if using a beat sheet, or 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans.
You should also scout for podworms as we enter the pod set and pod fill stages. We continue to find low levels of corn earworm in full season and now double crop soybeans, so be sure to scout fields on a routine basis. As trap catches increase, open canopy blooming fields will be the most attractive to egg laying moths. However, all fields should be scouted because as corn dries down all fields could be attractive to egg laying moths. A treatment should be considered if you find 3 podworms per 25 sweeps in narrow-row fields and 5 podworms per 25 sweeps in wide-row fields (20 inches or greater).