Agronomic Crop Insect Management – April 8, 2016

Joanne Whalen, Extension IPM Specialist;

Fields should be sampled for both for pea aphid and alfalfa weevil. When sampling for aphids and weevils, collect a minimum of 30 random stems throughout a field and place them top first in a white bucket. For aphids, count the number present per plant as well as any that have dislodged from the stem into the bucket. As a general guideline, you should consider a treatment in alfalfa less than 10 inches tall if you find 40-50 aphids per stem. The treatment threshold for alfalfa 10 inches or taller in height is 75-100 per stem. Although beneficial insects can help to crash aphid populations, cool temperatures will slow beneficial insect activity. As a general rule, you need one beneficial insect per every 50-100 aphids to help crash populations. For alfalfa weevil, you will want to record the number of weevil larvae per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision: up to 11 inches tall – 0.7 per stem; 12 inches tall – 1.0 per stem; 13 to 15 inches tall – 1.5 per stem; 16 inches tall – 2.0 per stem and 17 to 18 inches tall – 2.5 per stem. Information on treatment thresholds and options for insect management in alfalfa can be found at the following link:

Field Corn
As we approach planting time for most fields (as well as possible emergence of early planted fields), I have received questions this past week about management options for cutworms. As far as cutworm management, the following link from the University of Tennessee’s Crop News Blog provides a good review of cutworm management in corn using at-planting technologies: ( Factors that favor black cutworm outbreaks include late planting, heavy infestations of winter annual weeds before tillage and planting, reduced tillage, and corn panted into soybean stubble. Fields with a combination of these factors are more attractive to migrating moths and are likely candidates for egg laying. Even if an at-planting management technology was used, these fields should be monitored closely as corn emerges. Young larvae will feed on plants, resulting in small, irregular shaped holes. Black cutworms generally begin cutting plants at the fourth instar. One cutworm larvae can cut an average of three to four plants during its lifetime. In recent years and in variable locations throughout the state, we also find other cutworm species damaging very early emerging corn. In most cases, this damage is caused by the clay backed cutworm or the dingy cutworm. These species overwinter as half-grown larvae in the soil so they can get a “jump” on black cutworms. Regardless of species, a rescue treatment should considered in 1-2 leaf stage corn if you can find plants with 10% leaf feeding or 3% cut plants and larvae are present. At the 2 to 4-leaf stage, a treatment should be considered when you find 5% of the plants cut and larvae are present. Information on treatment thresholds and options for insect management in field corn can be found at the following link:

During the past week, I have also received calls about the availability of Avipel Hopper Box (dry) Corn Seed Treatment as a bird management option on field corn. This is a Special Local Needs Label (Section 24(c)) that is still available in Delaware for the 2016 season and expires on July 1, 2016. A copy of the 24(c) label must be in your possession to use this product. In past years, the 24(c) label and use directions were on the pesticide canister. However, if this is not case you will need to contact Chris Wade at the Delaware Department of Agriculture for a copy of the label and/or for additional questions (

Lastly, to help you keep track of Bt corn traits, efficacy, and refuge requirements for the 2016 season, Chris DiFonzo, Field Crops Entomologist from Michigan State University, has once again updated the Handy BT Corn Trait Table.

As part of an Extension IPM project titled “Incorporating a Total Crop Management Approach into Current Soybean Integrated Pest Management (IPM) Programs “, we are looking at evaluating and demonstrating the role of small grain cover crops in weed management, slug management and maintenance/improvement of soil health. Reports from the 2014 and 2015 seasons can be found at:


During our sampling for slugs in no-till fields using shingle traps last fall and this spring, we observed low to moderate levels of adult marsh and grey garden slugs. Although slugs were found under shingle traps in fields with and without cover crops, the fields with cover crops generally had higher numbers. In addition to using shingle traps, scouting for eggs and watching for egg hatch can help identify potential problem fields. More information on scouting for slug eggs can be found at the following link from Ohio State University:×600%29_-_20091222_04.03.14PM.html

Small Grains
As we see a return to warmer temperatures, be sure to scout fields on a weekly basis for cereal leaf beetles. Low levels of adult beetles and eggs continue to be found in fields throughout the state. The following link from North Carolina provides information on tank mixing insecticides with your nitrogen application in 2016:

Information on treatment thresholds and options for insect management in small grains can be found at the following link:

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