Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
Once again we are finding a few fields with whiteflies; however, populations are not as high as past years. They 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 provide 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 as well as an increase in grasshoppers and bean leaf beetles in full season and double crop fields. In a few cases, we are seeing fungal pathogens that can help crash caterpillar populations. Continue to use defoliation thresholds to make treatment decisions for these insects. Remember, that in addition to defoliation, grasshoppers and bean leaf beetles can feed on and/or scar pods.
Soybean loopers (which are also defoliators) continue to be found in fields throughout the state. As a reminder, they are not effectively control by the pyrethroids so materials labeled for soybean loopers like Belt SC, Besiege, Blackhawk, Radiant or Steward will be needed. Also, the highest labeled rate should also be used for soybean looper control.
Continue to watch for stink bugs in all fields during the pod development and pod fill stages. We continue to see an increase in populations, especially green stink bugs. You will need to sample for both adults and nymphs when making a treatment decision. As a general guideline, we are using a new threshold in the Mid-Atlantic Region: 5 stink bugs per 15 sweeps. This is the threshold for soybeans produced for grain. If you are producing soybeans for seed, the threshold is still 2.5 per 15 sweeps.
Corn earworm populations still remain low and spotty in most fields throughout the state. However, moth catches in pheromone traps at the end of this week still remain relatively high. Since population levels will vary from field to field, the only way to know if you have an economic level will be to scout all fields. Once pods are present, the best approach to making a decision on what threshold to use for corn earworm is to access the Corn Earworm Calculator developed at Virginia Tech (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter. As of the 2014 season, we still were able to achieve earworm control in soybeans using a pyrethroid as long as: (1) larvae were treated when threshold levels were present (not exploded population levels), AND (2) larvae were small at the time of application, AND (3) the highest labeled rate was used. If insects like soybean looper, beet armyworm or fall armyworm are in the mix, you will want to consider “worm” specific materials like Belt, Besiege, or Steward for the complex of larvae present. Over the next couple of weeks, another factor to consider when selecting a chemical will be the presence of corn earworm larvae resulting from migratory moths laying eggs in our fields that are resistant to pyrethroids. Lastly, if economic levels of stinkbugs are in the mix, you will need to add a pyrethroid to the “worm” specific materials like Belt or Steward. Besiege is a combination of a pyrethroid (lambda-cyhalothrin) and a “worm” specific material (chlorantraniliprole).
We continue to see soybean aphids in fields throughout the state. Remember, this aphid is more of a problem when the weather remains cooler. The economic threshold for soybean aphid established in the Midwest is 250 aphids per plant. Populations should be increasing and most of the plants should be infested (>80 percent) in order to justify an application. This threshold is appropriate until plants reach mid-seed set (R5.5). Spraying at full seed set (R6) has not produced a consistent yield response in the Midwest.