Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
Be sure to continue to scout carefully for earworms, especially in double crop soybeans, as well as defoliators during the next few weeks. Be sure to check all labels for the days between last application and harvest.
Consultants are starting to find small corn earworm larvae that are most likely the result of the recent increase in pheromone trap moth activity. Although we can find a few larger larvae in the mix, in most cases they are still relatively small. With the recent increase in pheromone trap catches, we will continue to see a new hatch of small larvae.
We continue to see an increase in stinkbugs, especially in full season fields. The population levels, as well as species, vary from field to field depending on your location in the state. In Sussex County, the predominant species are native green and brown stink bugs, although brown marmorated (BMSB) are in the mix. From the Milford and Harrington areas in Kent County through New Castle County, the BMSB is more commonly found in the mix. We are just starting to find a few hot spots of BMSB with the highest populations along woods edges. You will need to 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 large nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. Thresholds are based on numbers of large nymphs and adults (native green and/or brown stink bugs), as those are the stages most capable of damaging pods. As a general guideline, current thresholds are set at 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans. In Virginia, the threshold has been increased to 5 stink bugs in 15 sweeps.
Once again we are finding a few fields with whiteflies; however, populations are not as high as past years when soybeans were under heat and drought stress. Although we have limited experience with whiteflies in our area, whiteflies have generally not been a problem in the past, especially if moisture is adequate. They are related to aphids (that is they are in the same order of insects) and so can cause yellowing on the leaves if populations are high enough. The following links provides pictures of whiteflies and some additional comments regarding whiteflies in soybeans:
http://bulletin.ipm.illinois.edu/article.php?id=832
http://ipcm.wisc.edu/blog/2012/07/questions-about-whiteflies-in-soybean/
We continue to find a variety of defoliating caterpillars in soybeans including beet armyworm, yellow striped armyworm, green cloverworm, and soybean loopers. We are also seeing an increase in grasshopper populations in a few fields. All of these insects are defoliators and you will need to use percent defoliation to make a treatment decision. There are no available thresholds for the number of the above insects per sweep. Remember, that in addition to defoliation, grasshoppers can feed on and/or scar pods. In full season soybeans in the pod fill stage, the threshold is 10-15% defoliation. Remember, double crop soybeans cannot tolerate as much defoliation since they often do not reach the leaf area index needed for maximum yields. As a reminder, the pyrethroids have not provided effective control of beet armyworm or soybean loopers so a product labeled for these 2 species in soybeans will be needed if defoliation is present.
Since many of our pests in soybeans migrate to us from the south, the following two links provide information on what is occurring in Virginia and North Carolina: http://www.sripmc.org/Virginia/