Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
In general, corn earworm populations have not significantly increased since last week. You will need to watch double crop fields for the next couple of weeks since they will still be attractive to egg laying moths.
We continue to find economic levels of 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. BMSB populations are once again highest 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. Economic damage continues to occur on R-5 stage soybeans. 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.
In general, defoliating caterpillar populations, especially green cloverworm dropped off significantly this past week in full season soybeans. In many cases you can find diseased larvae both in the sweep net and sometimes attached to the leaves. In other cases, larvae present last week are gone this week. However, you will still need to watch double crop soybeans — they 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.
Favorable weather conditions have resulted in a continued increase in soybean aphid populations. The current economic threshold for aphids is an average of 250 aphids per plant through the R5 growth stage (3 mm long seed in the pod at one of the four uppermost nodes on the main stem) and the population is increasing. If you find 250 per plant you need to re-check in 3-4 days to see if the population is increasing. As indicated in information from Ohio were this insect can be more of a problem “this number is the action threshold, it is not the economic injury level (EIL) at which soybean aphid causes yield loss. Yield loss occurs when aphids reach 500-600 aphids per plant. Furthermore, these numbers do not apply to beans at R6 and later. The thresholds at these growth stages increase to over 1,000 aphids per plant.” As a reminder, this insect can be controlled by beneficial insects. You should also watch for natural enemies including lady beetles, parasitized aphids and fungal pathogens that can help to crash populations.
Since many of our pests in soybeans migrate to us from the south at this time of year, the following two links provide information on what is occurring in Virginia and North Carolina.
http://www.sripmc.org/Virginia/