Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Alfalfa
Continue to sample for potato leafhoppers on a weekly basis. Although adults are the main life stage present, we are starting to see the first nymphs. Both life stages can damage alfalfa but the nymphs can cause damage very quickly. 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.
If you have planted a glandular haired variety, we do not have any local data but here is some information from Ohio State regarding treatment thresholds on these varieties:
“If the alfalfa is one of the glandular-haired, leafhopper-resistant varieties of alfalfa, the economic threshold is three leafhoppers per inch of growth (24 leafhoppers for 8” tall alfalfa, for example). However, if the resistant alfalfa is a new planting this spring, growers should use thresholds meant for regular alfalfa during the first growth from seeding. Because resistance improves as the seedling stand develops, research suggests that the threshold for a resistant variety can be increased after the first cutting.”
Field Corn
Continue to watch for true armyworm moving from barley into adjacent corn fields. In many cases, larvae will be large and control will be difficult once larvae move deep in whorls. Remember, worms must be less than 1 inch long – some labels indicate that larvae need to be even smaller – to achieve effective control. The treatment threshold for true armyworms in corn is 25% infested plants with larvae less than one-inch long.
Once again there are reports of sugar cane beetle attacking seedling stage corn in North Carolina and a few counties on the lower eastern shore of Maryland. Last season, the damage was confused in some cases with wireworm and/or below ground cutworm feeding so be sure to learn about this insect and the type of damage it can cause when you are sampling corn fields. So far, I am not aware of any fields being attacked in Delaware but it does appear this insect could be expanding its range. The link to an article written by Dominic Reisig (Extension Entomologist from NC State) provides information on how to diagnose the injury as well as control information (http://www.nccrops.com/2013/05/24/sugarcane-beetle-showing-up-in-corn/). Unfortunately, there are no rescue treatments to control this insect pest.
Small Grains
We are still finding pockets of armyworms, grass sawflies and cereal leaf beetles in wheat and barley that has not been treated so be sure you continue scouting for all three pests. As far as cereal leaf beetle, research from Virginia and North Carolina indicates that the greatest damage can occur between flowering and the soft dough stage.
Soybeans
Be sure to sample fields starting at emergence for bean leaf beetles and grasshoppers. In the earliest planted and emerged fields, we have started to see an increase in activity for both insects. As barley is harvested and soybeans are planted, these fields will be especially susceptible to attack from grasshoppers and feeding can often cause stand loss. If stand reductions are occurring from plant emergence to the second trifoliate, a treatment should be applied. Although no precise thresholds are available, a treatment may be needed if you find one grasshopper per sweep and 30% defoliation from plant emergence through the pre-bloom stage. As a general guideline, a treatment may be needed for bean leaf beetle if you observe a 20 – 25% stand reduction and/or 2 beetles per plant from cotyledon to the second trifoliate stages.
Although it is still too early to tell what will happen with Kudzu Bug in Delaware soybean fields, it does appear that we will need to watch carefully for this insect in 2013. My colleague in Virginia, Ames Herbert, is reporting very early adult activity (http://www.sripmc.org/Virginia/archives.cfm ). We did not encounter any in our 2012 survey funded by the Delaware Soybean Board but 2013 could be a different year. Please refer to the following links for pictures of adults and nymphs as well as management strategies (http://www.kudzubug.org/index.html).