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.
In areas of the state with high bean leaf beetle counts, be sure to watch for both defoliation and pod feeding. Be sure to check the following link for the most recent decision making information for this insect pest from the Midwest (http://www.extension.iastate.edu/CropNews/2008/Issues/20080728.htm).
We have received reports of adult and immature spider mite populations declining in some areas of the state; however, eggs are still present in fields. The recent cooler mornings and humid days have been favorable for the development of diseases that can crash populations. However, be sure to check fields within 3 days if high levels of eggs are present in fields. As temperatures increase again, we could see a re-bound in populations. In addition to dimethoate, Lorsban and Hero, it should also be noted that the high rate of Brigade is labeled for mites on soybeans.
You should also scout for soybean aphids. We have just found the first soybean aphids in Kent and Sussex Counties. We are finding very low levels; however, they are building in the western states and we often see more moving to our area after this occurs. Also, as a reminder, this is more of a cool season aphid. 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 stage 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 stink bug) 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 podsworms 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).