Agronomic Crop Insects – September 9, 2011

Joanne Whalen, Extension IPM Specialist;

We continue to find corn earworms in soybeans. If you have not checked your fields, be sure to sample fields so you do not miss a late hatch of larvae. We can still find moths laying eggs in fields. Although trap catches appeared to be declining on Sept 5, our most recent trap catches showed an increase again. You should also check the recent report from VA regarding their high trap catches and recent, new infestations (

A number of defoliators are still present in double crop beans including bean leaf beetles, grasshoppers, and in some cases hot spots of beet armyworm. The threshold for defoliation will need to be reduced if a mixed population is present. Although soybean looper populations still remain low, there are reports from the southern states of building populations. Be sure to check my comments from last week’s newsletter regarding soybean loopers. In addition, the following link also provides useful information for managing this important defoliator.

This past week I received a question about lodging in double crop soybeans. It appears that damage may have been caused by an insect pest that is rarely seen in soybeans, the lesser corn stalk borer. Although I have never observed this pest in soybeans in Delaware, there have been a number of reports of this pest in states to our south this past season (especially North Carolina and Tennessee). Information from the south indicates that it is primarily a problem in late planted fields grown in sandy soils. In addition, it is most often found in areas of the field where there is little or no small grain stubble. The following links provide information on this insect pest.

Small Grains
As you make plans to plant small grains, you need to remember that Hessian fly can still be a problem. Since the fly survives as puparia (“flax seeds”) in wheat stubble through the summer, you should still consider this pest as you make plans to plant small grains. In our area, damage has been the result of spring infestations. Plants attacked in the spring have shortened and weakened stems that may eventually break just above the first or second node, causing plants to lodge near harvest. Warm fall weather conditions can extend fly emergence and egg-laying beyond the fly-free dates, but these dates should still be used as a guideline for planting. Since we rarely see plants stunted in the fall, we still feel that most of the damage we see is occurring from spring infestations. Plants attacked in the fall at the one-leaf stage may be killed outright. Wheat attacked later in the fall will be severely stunted, with the first tillers killed and plant growth delayed. Plants infested in the fall can easily be recognized by their darker than normal bluish coloration and leaves with unusually broad blades. Combinations of strategies are needed to reduce problems from Hessian fly:

● Be sure to completely plow under infested wheat stubble to prevent flies from emerging.

● Avoid planting wheat into last season’s wheat stubble, especially if it was infested with Hessian fly.

● Avoid planting wheat next to last season’s wheat fields – the most serious infestations can occur when wheat is early planted into wheat stubble or into fields next to wheat stubble.

● Eliminate volunteer wheat before planting to prevent early egg-laying.

● Do not use wheat as a fall cover crop near fields with infestations.

● When possible, plant after the fly-free date. (Oct 3 – New Castle County; Oct 8 – Kent County; Oct 10 – Sussex County).

● Plant resistant varieties. You should look for varieties that have resistance to Biotype L. You will need to check with your seed dealers to identify varieties that our adapted our area.

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