Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
Continue to sample fields on a weekly basis for leafhoppers as well as defoliators including earworm, webworms and fall armyworms.
Soybeans
As of this date, economic levels of corn earworm larvae have been reported in fields in Sussex County. Although Sunday’s moth catch (August 30) was high at all locations, the most recent blacklight trap catches (Sept 3) are showing a decline due to the recent cool nights. In comparison, pheromone trap catches remain high in a number of locations. It appears that the corn earworm hatch may have been delayed due to the recent cool evening temperatures. With the warmer weather predicted for the end of the week and weekend, fields should be scouted carefully for corn earworm larvae. The only way to know if you have an economic level will be to scout and treat when worms are small — do not wait until you see pod damage. It will be important to spray when worms reach threshold. The Corn Earworm Calculator (http://www.ipm.vt.edu/cew/) developed in Virginia estimates a threshold based on the actual treatment cost and bushel value you enter. When selecting an insecticide, be sure to check all labels for the days from last application to harvest as well as other restrictions.
With the recent cooler temperatures, we have seen a significant increase in soybean aphid populations in double crop fields on the western side of the state, especially in Kent and Sussex counties. As a general guideline, treatment is needed through the R-5 stage (seed is 1/8 inch long in the pod of one of the four uppermost nodes on the main stem) of soybean development if economic levels are present. It may also be beneficial to spray through R-6 stage (pods containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem) — reports vary as to the benefit of spraying once plants reach the R-6 but in some years and some situations there has been an economic return. Spraying after R-6 stage has not been documented to increase yield in the Midwest. The suggested treatment threshold from the Midwest is still 250 aphids per plant with an increasing population.
Lastly, there are also a number of defoliators still present in double crop soybeans including bean leaf beetles, grasshoppers, and green cloverworms. The pest complex varies from field to field. The threshold should be reduced if a mixed population is present. As a reminder, both bean leaf beetles and grasshoppers can also feed on pods.
Small Grains
With the increase in no-till wheat acreage as well as our typical rotation of wheat following corn, it will be important to consider a number of insect pests that can present problems. Last season there was a nice article in the Kentucky Pest News entitled “Insect Pest Management Decisions in Preparation for Planting Wheat” that should be reviewed since it does a nice job of addressing insect pests that pose a threat to wheat in the fall including aphids, the wheat curl mite, Hessian fly and fall armyworm. (http://www.uky.edu/Ag/kpn/kpn_08/pn080825.htm#wheins). 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.