Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
Continue to sample fields on a weekly basis for defoliators including earworm, webworms and all armyworm species. Economic levels of defoliators, especially corn earworm and beet armyworm continue to be found causing damage.
Soybeans
Even after the hurricane, economic levels of corn earworm, and in some case a second hatch of small larvae, continue to be found in double crop fields in all 3 counties. Monday’s moth catch remained high so you will need to continue to watch fields through the next two weeks for newly hatched larvae.
In addition, economic levels of stink bugs continue to be found in fields throughout the state. Depending on the part of the state, we can find native green and brown stink bugs as well as brown marmorated stink bugs. So far, the highest concentrations of brown marmorated stink bugs are still being found in Kent and New Castle Counties, especially along field edges bordered by woods. Fields will need to be scouted through the pod development and fill stages (through R-6 and some studies say R-7) to avoid damage from stinkbugs which can include underdeveloped or aborted seeds, green stem syndrome, reductions in pod fill, seed vigor and viability, yield loss and a reduction in the storage stability of harvested seeds. Although there are a number of thresholds used in states to our south, we continue to use the same threshold for native green and brown stink bugs that is being used in Virginia (2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans). As a reminder, currently, there are no thresholds established for brown marmorated stink bugs in soybeans. The following link written by my colleague Dr. Cerruti Hooks from the University of Maryland provides a detailed overview of stink bugs and soybeans (http://dorchester.umd.edu/files/August_18_2011.pdf).
Although we have not heard of any reports of soybean loopers from the south, this is an insect that can catch folks by surprise since it can quickly defoliate a field. So as you are sweeping fields be sure to watch for insect as well. Soybean loopers are a migratory pest, and in the states to our south resistance to pyrethroids has been documented. We also have cabbage loopers (also a migratory insect pest) which can be present at the same time and they are generally controlled by pyrethroids. Identification can be difficult because although there is a “black footed” phase of the soybean looper there is also a “green phase” that can be confused with cabbage loopers. One characteristic that might help is the presence of microspines on soybean loopers that are not present on cabbage loopers; however, you will need high magnification to see the microspines. The following link from VA provides information from last season (2010) as well as images of both color phases:
http://ipm-virginia.blogspot.com/2010/09/soybean-loopers-turning-up-in-higher.html.
NOTE: As we get closer to harvest, be sure to check all labels for the days from last application to harvest as well as other restrictions.
Small Grains
As you make plans to plant small grains, it will be important to consider a number of insect pests that can present problems, especially in early planted fields. The following article continues to provide a good review of insect pests that pose a threat to wheat in the fall including aphids, the wheat curl mite, Hessian fly and fall armyworm. In addition to the insect pests listed in this article, true armyworms have been a pest in the past as well as slugs if we have a wet fall. (http://www.uky.edu/Ag/kpn/kpn_08/pn080825.htm#wheins).