Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
After the first cutting and on any new plantings, be sure to watch for the first leafhoppers. Once plants are yellow, yield loss has already occurred. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa.
Field Corn
Continue to watch seedling stage fields for both cutworm and slug damage, especially in no-till corn fields. It is important to check all fields for cutworms, even where at-planting treatments were used. The treatment threshold is 3% cut plants in spike to 3-leaf stage corn. In addition to cut plants, be sure to watch for leaf feeding which can be an indication of the potential for significant cutting damage and yield loss. Please visit the following link for pictures of leaf feeding:
http://www.ent.iastate.edu/imagegal/plantpath/corn/bcutworm/1287bwcholes.html
The weather continues to be very favorable for slug damage and we continue to see fields with economic levels of damage. Although they are generally a problem in fields with heavy no-till covers and a history of problems, we are finding problems in fields with no history of problems so be sure to check as soon as plants are spiking out of the ground. Materials labeled for slug management in field corn include Deadline M-Ps (the main metadelhyde product available), Sluggo (iron phosphate) and IronFist (sodium ferric FDTA). In years past, 30% nitrogen applied at night when the plants are dry and there is no wind has resulted in variable levels of success since you must contact the slugs. The rate used in past years was 20 gallons per acre of 30% N on corn in the spike to one-leaf stage and the mix was cut 50/50 with water to reduce – but not eliminate – plant injury.
Small Grains
We continue to find low levels of newly hatched armyworm larvae and an occasional medium size grass sawfly larvae in barley and wheat fields. We also continue to find economic levels of cereal leaf beetle damage. The greatest damage from cereal leaf beetle can occur between flowering and the soft dough stage. Population levels remain variable throughout the state so scouting fields will be the only way to determine if an economic level is present.
Although armyworm can attack both wheat and barley, they can quickly cause significant losses in barley. Heavy defoliation of the flag leaf can result in significant economic loss. Armyworms generally begin head clipping when all vegetation is consumed and the last succulent part of the plant is the stem just below the grain head. Larvae can feed on the kernel tips of the wheat, resulting in premature ripening and lower test weight.
Soybeans
Seed corn maggot can be a problem in no-till soybeans as well as conventional soybeans where a cover crop is plowed under immediately before planting or where manure was applied. All of these situations are attractive to egg laying flies. Control options are limited to commercial applied seed treatments containing an insecticide. Labels state early season protection against injury by seed corn maggot. No rescue treatments are available for this insect pest.