Agronomic Crop Insect Management – May 6, 2016

Joanne Whalen, Extension IPM Specialist;

Be sure to check for alfalfa weevil adults and larvae within a week of cutting, especially if populations were above threshold before cutting. Feeding from both stages can hold back re-growth. After cutting, there needs to be enough “stubble” heat to control the weevils with a cutting. A stubble treatment will be needed if you find 2 or more weevils per stem and the population levels remain steady.

Field Corn
Be sure to watch for both cutworms and slugs feeding in newly emerged corn fields. We can find damage from slugs and cutworms, especially in no-till fields. As a general guideline, a treatment is recommended for cutworms if you find 10% leaf feeding or 3% cut plants. If cutworms are feeding below the soil surface, it will be important to treat as late in the day as possible, direct sprays to the base of the plants and use at least 30 gallons of water per acre. For cutworms, fields should be sampled through the 5-leaf stage for damage. With the current cool, rainy weather, we have seen a significant increase in slug damage. If slugs are damaging plants, you will be able to see “slime trails” on the leaves. Materials available for slug management include Deadline M-Ps (the main metadelhyde product available), Sluggo (iron phosphate) and IronFist (sodium ferric FDTA).

Small Grains
Aphids, grass sawflies, true armyworms and cereal leaf beetles can be found in fields throughout the state.

Cereal Leaf Beetle – We have seen a significant increase in cereal leaf beetle populations, especially in fields with a history of problems. Economic damage can occur in both barley and wheat. Research from Virginia and North Carolina indicates that the greatest damage from cereal leaf beetle can occur between flowering and the soft dough stage. For more information on monitoring and management, please visit the following link:

Armyworms and Grass Sawfly – Low levels of true armyworm moths can be found in our light traps. Although armyworm can attack both wheat and barley, they can quickly cause significant losses in barley. As a reminder, both overwintering and migratory moth populations are responsible for our infestations. As indicated in previous newsletters, trap counts in Kentucky have been lower than their rolling 5-year averages ( For more information on monitoring and management, please visit the following link:

Aphids – With the current weather conditions, you will also need to watch for aphids feeding in the heads of small grains. The treatment threshold is 15-25 aphids per head with low beneficial insect activity. A ratio of one predator to every 50 to 100 aphids is often sufficient to achieve biological control. However, with the current cooler temperatures, aphids reproduce rapidly whereas their natural enemies reproduce slowly and lag behind. If the crop is approaching the hard-dough stage and there is good beneficial insect activity, no control should be needed.

Native Brown Stink Bugs – We continue to see an increase in the number of native brown stink bugs in barley and wheat. In years past, we have seen native brown stink bugs in barley and wheat but so far we have not felt that we have seen any losses. Research from the South in the early 1980s showed that the milk stage of development is most susceptible to damage from stink bugs by reducing grain weight and germination. Additional information indicates that wheat may be susceptible to native stink bug feeding from the milk through soft dough stages. Once wheat reaches the hard dough stage the likelihood of damage from stink bug is diminished greatly. Thresholds in the South for native stink bugs in wheat range from one per head to one per 5 to 10 heads.

New Aphid Species – Although not known to occur in the Mid-Atlantic Region, there is a new aphid species occurring in small grains in the south — so far it has been found in Alabama and South Carolina. The range of expansion has been slow but you should be aware of it as you are scouting small grains. For more information, please visit the following link:

If you think you are finding this aphid species, it is important that you contact Steve Hauss at the Delaware Department of Agriculture by email ( or call (302) 698-4500 for official confirmation since this would be a new detection in Delaware.

Banded Wing Fly
Each year I receive questions about an adult fly that can be easily found in no-till fields. The fly is the banded wing/picture-wing fly and is present in fields due to the heavy covers in many fields ( Adult flies are generally attracted to rotting plant material and larvae develop on decaying organic material.