Joanne Whalen, Extension IPM Specialist;jwhalen@udel.edu
Alfalfa
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. 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.
If slugs are damaging plants, you will be able to see “slime trails” on the leaves.In fields that are just emerging we may see more injury from slugs that have just started to hatch in the last week. Old existing stocks of Deadline M-Ps should be available for slug management this year in field corn. Additional products available for slug management in field corn include Sluggo (iron phosphate) and IronFist (sodium ferric FDTA).
Small Grains
Grass sawflies, true armyworms and cereal leaf beetles can be found in fields throughout the state. Population levels of all 3 insects remain variable so scouting fields will be the only way to determine if an economic level is present. Research from Virginia and North Carolina indicates that the greatest damage from cereal leaf beetle can occur between flowering and the soft dough stage. Although armyworm can attack both wheat and barley, they can quickly cause significant losses in barley. We are also seeing an increase in aphid numbers so you will also need to watch for aphids feeding in the heads of small grains. The treatment threshold is 20-25 aphids per head with low beneficial insect activity.
This past week we have seen an increase in the number of native brown stink bugs in barley and wheat. In years past, we have seen brown stink bugs in barley and wheat and so far we have not felt that we have seen any losses. In states to our south where stink bugs are more of a problem in wheat they indicate that it is not uncommon to find stink bugs in small grains after head emergence. However, it takes extremely high numbers to cause economic damage to heading wheat. Research from the early 80s showed that the milk stage of development is most susceptible to damage from stink bugs by reducing grain weight and germination. Once wheat reaches the hard dough stage the likelihood of damage from stink bug is diminished greatly.