Agronomic Crop Insects – September 7, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Soybeans
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. Although trap catches appeared to be declining on September 3, we will need to watch trap catches at the end of this week to see if this trend continues. In addition, we need to watch what happens in states to our south.

A number of defoliators are still present in double crop beans. The threshold for defoliation will need to be reduced if a mixed population is present. Although soybean looper populations remain low, there are reports from the southern states of building populations.

In New Castle and Kent Counties, we are a finding a few more fields with high levels of Brown Marmorated Stink Bugs on field edges of full season soybeans. Although we do not have a threshold for BMSB, we are also finding levels that we use as a threshold for native stinkbugs (2.5 per 15 sweeps) along the edges of double crop fields in New Castle County. Native stink bugs populations continue to be at threshold levels in fields throughout the state.

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 generally 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. 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.

● 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.

The following link from Alabama provides additional information on Hessian Fly Management (http://www.aces.edu/dept/grain/HessianFly.php

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