Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
Be sure to continue to scout carefully for earworms during the next few weeks. Also, as we get closer to harvest be sure to check all labels for the days between last application and harvest.
Threshold levels of corn earworm continue to be found in fields throughout the state but they are not present in every field. Although we can find various sizes of larvae, in most cases they are still relatively small. In addition they are being found in some full season (especially where canopy is not closed) and double crop fields so the only way to know if you have an economic level will be to scout. If fields were already sprayed, be sure to watch for newly hatched larvae. With the sustained flights, there could be a new hatch of small larvae.
Since last week’s report, we also are starting to find an increase in stinkbugs, especially in full season fields. Like corn earworms populations, the 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. From the Harrington area through New Castle County, the brown marmorated stink bug can be found in the mix. In some fields, there continue to be hot spots of brown marmorated stink bugs with the highest populations generally still 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. We are currently following the same guidelines that are being used in Virginia. 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.
Similar to 2010, there are fields with high levels of whiteflies. Although we have limited experience with whiteflies in our area, as far as we know, whiteflies have not been a problem in the past even when we have seen what folks describe as “clouds of whiteflies”. 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. Damage is most likely to occur when beans are stressed. The following link provides pictures of whiteflies and some additional comments regarding whiteflies in soybeans: http://bulletin.ipm.illinois.edu/article.php?id=832.
For more information on what is occurring in Virginia, you will want to look at the Virginia Ag Pest Advisory: http://www.sripmc.org/Virginia/.