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Issue No. 5, Article 2/May 4, 2012

Scouting for Black Cutworm Larvae Should Be Underway

Growers should begin scouting emerging corn seedlings for signs of leaf feeding and cutting by black cutworms. Significant moth flights in late March and early April could result in cutting-stage larvae in many areas of the state in the coming weeks (Figure 1).


Figure 1. Projected potential cutting dates in Illinois for black cutworm larvae.

Potential cutting dates are determined by using the reports of intense captures (9 or more moths in a 1- to 2-night trapping period) and calculating degree-day accumulations using historical temperature data. We can expect 4th-instar larvae to be present after the accumulation of 300 degree-days (Table 1).

Table 1. Development of black cutworms based on degree days accumulated (base 50°F) after an intense capture of adults.

Accumulated degree days

First occurrence

General activity

0

First intense moth flight

--

90-311

1st through 3rd instars

Leaf feeding

312-364

4th instar

Cutting begins

365-430

5th instar

Cutting

431-640

6th instar

Cutting slows

641-989

Pupa through adult

Mating and egg laying

Adapted from L.V. Kaster and W.B. Showers. 1994. Modeling black cutworm (Lepidoptera: Noctuidae) field development in Iowa. Environmental Entomology 13:384-389.

Feeding by early instars (1st–3rd) appears as pinhole injury on leaves. By the time the larvae become 4th instars, they begin cutting plants off and dragging them into their "burrows" to feed. As larvae grow through their 6th or 7th instars (the number depends on diet and temperature), they require increasingly more food, so the larger larvae may cut off several corn seedlings. Depending on temperature, larvae develop over 28 to 35 days. More information on black cutworm life cycle, injury, and scouting procedures can be found in the black cutworm factsheet.

We encourage you to scout cornfields in your area for black cutworm injury; as always, we welcome reports of what is being seen in the fields.--Kelly Estes, Illinois Natural History Survey

Author:
Kelly Estes

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