Agronomic Insect Update – May 11, 2018

David Owens, Extension Entomologist, owensd@udel.edu

Alfalfa
Continue scouting for alfalfa weevil defoliation. Alfalfa weevil are light green with a small black head and no legs. This is very different from armyworm which do have legs and are quite a bit larger and with a large head. I heard of a case last week in a nearby state where weevils were misidentified as worms and an ineffective product was applied. Also watch out for potato leaf hoppers causing ‘hopperburn’ – a yellowing around the leaf margins. Leafhoppers this early are more damaging on new alfalfa plants and after the first cutting. We have a fact sheet on potato leaf hopper that can be found here: http://extension.udel.edu/factsheets/potato-leafhopper-control-in-alfalfa/.

Small Grains
Cereal leaf beetle larvae can be found in fields at low numbers. Our threshold is 25/100 tillers. Sawflies also started showing up in fields, and true armyworm moth activity is starting to increase. Not every product labeled for armyworm is labeled for sawfly, so be sure to identify the critters accordingly. When two pests that feed in a similar manner show up in a field at below threshold numbers, a conservative approach would be to sum their population proportion of threshold and treat accordingly. For more management considerations of both sawfly and armyworm, see this week’s guest the past answer for last week’s.

Corn
Be sure to scout seedling corn for evidence of wire worm, white grub, armyworm, and cutworm pests. Armyworms and cutworms tend to be more active in fields with recent small grain cover crop. Management recommendations for corn pests can be found at: http://extension.udel.edu/ag/insect-management/field-corn/.

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