Agronomic Crop Insects – September 2, 2016

Joanne Whalen, Extension IPM Specialist;

In Kent and Sussex counties, we have seen an increase soybean looper and beet armyworm populations. As a reminder, these two insects are not effectively controlled by the pyrethroids. Materials labeled for soybean looper and beet armyworm including Besiege, Blackhawk, Coragen (NOTE – Prevathon is not labeled in DE) Radiant or Steward will be needed. The highest labeled rate is generally needed for soybean looper and beet armyworm control.

We are just starting to find fields with economic levels of native green stink bugs, especially in fields that have reached the R-5 stage which is described as the beginning seed stage (seed is 1/8 inch long (3 mm) long in the pod at one of the four uppermost nodes on the main stem). You will need to sample for both adults and nymphs when making a treatment decision. Available thresholds are based on beans that are in the pod development and fill stages. Studies from the South say that scouting is needed until beans are in the R-7 growth stage (beginning seed maturity) to avoid damage from stinkbugs which can include underdeveloped or aborted seeds, green stem syndrome, reductions in pod fill, seed vigor and viability, yield loss and a reduction in the storage stability of harvested seeds. 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.

We continue to find corn earworm (CEW) larvae in both full season and double crop fields but populations are spotty and levels remain low in most cases. Trap catches earlier in the week were similar to the end of last week, with a few locations still catching high numbers (Dover, Milford, Wyoming and Seaford). 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. Although it has been extremely hot and dry in most areas of the state, a combination of early morning dews, rain, and hot, humid day time temperatures can help increase the incidence of fungal pathogens that can help to regulate populations. However, only scouting will tell if this is occurring. 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 ( which estimates a threshold based on the actual treatment cost and bushel value you enter. You should also follow what is happening in areas to our south related to CEW pyrethroid resistance and chemical selection (( Most of the population we will see in soybeans will come from moths migrating from the south. Besiege, Blackhawk, Coragen, Radiant or Steward are all labeled for corn earworm control in soybeans.

NOTE – not all materials mentioned in southern newsletters are labeled in Delaware so be sure to check both the federal and state labels before applying an insecticide. Also, as we approach harvest, be sure to check insecticide labels for the pre-harvest interval (PHI) which is the number of days that must pass between the time of the last application of a pesticide and when the crop can be harvested.

Small Grains
As you make plans to plant small grains, you need to remember that Hessian fly can still be a problem. We did see an increase in populations in a few fields in the spring of 2016 –- so it is still present in the region. 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. Although damage in our area has generally been the result of spring infestations, we can see damage in the fall. 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. 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 be recognized by their darker than normal bluish coloration and leaves with unusually broad blades. The following combinations of strategies are needed to reduce problems from Hessian fly:

(a) Completely plowing under infested wheat stubble to prevent flies from emerging.

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

(c) 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.

(d) Eliminate volunteer wheat before planting to prevent early egg-laying.

(e) Do not use wheat as a fall cover crop near fields with infestations.

(f) Plant after the fly-free date. New Castle County- Oct 3, Kent County – Oct 8, Sussex County- Oct 10.

(g) 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 (

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