Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Small Grains

Recent cool wet weather should encourage entomopathogens of aphids. Lady beetle activity has been noticeable in other crops, suggesting that aphid pressure be reduced compared to recent years. However, warm weather in the week ahead will allow aphids to increase in number rapidly.

Alfalfa

Alfalfa weevil adults and larvae continue to be active. Select 30 stems by randomly walking to six locations and plucking stems from those locations. Take a few of the stems at a time and beat them vigorously against the side wall of a bucket to dislodge weevil larvae. Also measure the length of a few of those stems to get an average stem height. Penn State has a great alfalfa weevil control fact sheet with a dynamic threshold table based on stem height, value of the hay, and control costs. We incorporated the table into the UD Insect Control in Alfalfa document which can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/commercial-field-crop-pest-management/alfalfa/. Be advised that small weevil larvae often hide in the half folded terminal leaflets and are not easy to dislodge. You may want to visually examine the terminals after shaking stems.

When making an insecticide application, use higher water volume rates to ensure good coverage, especially into the terminals. Do not apply an insecticide a couple of days before or after a significant cold spell. Weevil larvae need to be active to come into contact with treated foliage. Keep good records of previous applications and be sure to scout fields after application. We can have new weevil hatch after a spray, justifying a second and sometimes even a third application prior to cutting. Our insecticide selection is very limited in alfalfa, and for this reason it is possible that besides environmental factors there can be some intrinsic factors in your local population that could render them less susceptible to a given insecticide if it has been used continuously for a long period of time. Adding to this concern is the chlorpyrifos tolerance revocation effective February 28, 2022. In last year’s spray trials, pyrethroids provided between 40 and 70% efficacy three weeks after application. Carbaryl initially provided a 70% reduction in alfalfa weevil but residual activity was very short and weevil counts increased afterwards. The most consistent active ingredient has been indoxacarb (Steward). It has a supplemental 2ee label for reduced rates, 4.0 to 11.3 fl oz per acre as opposed to the main label rate range of 6.7 to 11.3 fl oz. It also provided excellent residual control in last year’s trial at the 6.7 fl oz rate. FMC advises lower rates should have about 8-14 days residual, higher rates up to 21 days. When making an application to alfalfa, industry recommends including an spreader sticker type adjuvant such as an organosilicone to improve coverage. As always, make sure to read the labels of all products applied or tank-mixed to make sure there are no insecticide/adjuvant/herbicide concerns.

Early Season Moth Trapping

This week we had a decent cutworm flight near Harrington. Recent southerly winds and warmer weather have most likely contributed to this increase. Please note that trapping data is meant to be correlative over time, we do NOT have thresholds or make recommendations for individual fields or crop considerations based on them. We do not know at what point do these traps indicate a potential problem, short of comparing true armyworm counts to some long term data collected by University of Kentucky. Many thanks to Joanne Whalen for assisting with trapping efforts.