Agronomic Crop Insects – September 6, 2013

Joanne Whalen, Extension IPM Specialist;

As far as defoliators, we are starting to see an increase in grasshoppers and bean leaf beetles in double crop soybeans. Bean leaf beetles are generally being found in the “western” areas of the state from Greenwood to Middletown. Although both insects can defoliate soybeans it is also important to consider their ability to feed on pods resulting in the potential for moldy beans this fall. There are also reports from the south of an increase in soybean looper populations and we continue to find them as we sample. They often occur in hot spots and can quickly defoliate plants, so be sure to continue to watch for this insect. As a reminder, the pyrethroids will not provide effective control of soybean looper so Belt, Besiege, Blackhawk or Steward will be needed.

We continue to find economic levels of stinkbugs. 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 (BMSB, native green and/or brown stink bugs), as those are the stages most capable of damaging pods. As a general guideline, thresholds in the past were set at 2.5 per 15 sweeps in narrow-row beans, or 3.5 per 15 sweeps in wide-row beans. This threshold has been increased to 5 stink bugs in 15 sweeps. Once soybeans reach mid R-6 and R-7 (beginning seed maturity) , studies from the south say that scouting is still needed to avoid quality 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.

Cooler weather conditions continue to favor soybean aphids and this insect can be found in fields throughout the state. 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) with an increasing population so you need to check fields at least twice before making a treatment decision. 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 so be sure to watch for natural enemies including lady beetles, parasitized aphids and fungal pathogens that can help to crash populations. Although beneficial insect activity has increased in some fields, the cooler temperatures have slowed up their activity in others so it could take time to see reductions in aphid populations from beneficial insects.

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. 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. (Oct 3 in New Castle County; Oct 8 in Kent County; and Oct 10 in Sussex County).

(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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