Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Updated Insect Control Recommendations for alfalfa, small grains, soybean, and corn have been posted to the UD insect pest management webpage: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/vegetable-fruit-field/. Significant changes were made to alfalfa, corn and soybean, adding additional sampling and action threshold information for several pests, adding a couple of pest sections, and including mention of various generic insecticides at the end of each guide. A sorghum guide will be forthcoming soon.

Small Grain and Early Season Insect Trapping
We have reached predicted cereal leaf beetle egg lay in Georgetown. Last year, peak egg lay occurred about two weeks after reaching this degree day target. I have not heard of any reports suggesting significant cereal leaf beetle activity in the area, but if in doubt, scout!

A reported sighting of small true armyworm in the southern part of the state came in this week. The good news is that so far, moth flight activity has been low/normal. University of Kentucky has been trapping both true armyworm and black cutworm since 1993. In 2008, they experienced widespread outbreaks of true armyworm. Counts peaked many times higher than what they are currently trapping http://ipm.ca.uky.edu/awgraph. I mention UK’s data because armyworm activity in our pheromone traps do not suggest that this year will have unusual worm activity in small grains. Trap counts for the week are as follows, with thanks to Joanne Whalen, Emily Zobel, and Maegan Perdue.

Location TAW/night BCW/night
Willards, MD 1.7 1
Salisbury, MD 0
Laurel 0.4 5.1
Seaford 27.9 8.1
Harrington 8.9 5.3
Pearson’s Corner 7.7 1.6
Sudlersville, MD 1 2.7
Smyrna 10.4 1.1

 

Alfalfa
Alfalfa weevil larvae ranged from 1st to 3rd instar at the end of last week in northern Sussex and some fields were above threshold and treated. Be sure to monitor the fields after treating; Virginia has seen isolated areas where some products achieved only poor control. For those of you in the northern part of the state, be sure to sample your alfalfa if you have not already.

Corn
Scout planted fields as soon as you have emergence for slug feeding. The weather forecast is conducive to slug activity, and slug eggs are hatching out. Be especially wary on no-till fields with a history of slugs and fields with brassica cover crops. There is anecdotal evidence from neighboring states that brassicas favor slug populations. There are no thresholds for slug feeding, and the good news is that corn is much more difficult to kill from slug feeding than soybean, but if you are seeing significant defoliation, slugs number 3 or more per square foot, and the forecast is calling for cloudy, wet weather you are at risk for continued slug feeding and slower plant growth.

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