|
|
|
|
| Armyworm
as a Pest of Field Corn Pseudaleta unipuncta (Haworth) |
||||
|
|
||||
| The armyworm, Pseudaleta unipuncta (Haworth), is a native species widely distributed throughout the United States east of the Rocky Mountains. It has long been known to be an occasional serious pest of small grains and corn. However, with the increase of reduced-tillage culture and planting corn into sod and rye cover crops, armyworm damage to corn has increased sharply during the past decade. |
Photo by Marlin E. Rice |
|||
The armyworm primarily feeds on plants in the grass family but under hunger stress also will attack some legumes and other plants. Conventional-tilled corn is seldom damaged. Problems most frequently occur in reduced-tilled corn planted in old sod or grassy fields. First generation larvae active from mid-May to mid-June, cause extensive defoliation to small corn plants. Stand losses are usually low to moderate but in some cases may be severe enough to warrant replanting. |
||||
| Description | ||||
|
The moths are uniformly pale brown. There is a prominent white dot near the center of the front wings, and the wing-spread is about 11/2 inches. The moths hide in the grass and trash during the day. Strong flyers, they are active at night. The eggs, white with a light greenish cast, are laid in clusters or rows on lower leaves of grass and corn plants. The grass leaf is frequently folded lengthwise, partially covering the eggs. Newly hatched larvae are mostly pale green. During the day, they hide in the folded leaves in the whorl of the corn plant. Upon becoming about half grown (3/4 to 1 inch) their body color becomes basically brown with considerable color variation among individual worms. Full-grown worms are about 1 1/2 inches in length with a narrow broken white stripe down the center of the back. There also are stripes along each side of the body. The larvae feed on the leaves at night. The caterpillar stage lasts about 3 weeks, but the caterpillars are usually 10 to 14 days old before damage is noticed. By this time, many of the larvae will have small, white eggs stuck to their bodies just back of the head. These eggs hatch into parasite maggots which enter the body. Those larvae that reach maturity dig into the soil to pupate. Next generation moths emerge about 15 to 18 days later. |
||||
| Life History | ||||
|
|
||||
|
Armyworms overwinter as partially grown larvae under plant trash and in clumps of grass, and as pupae in the soil. Moths emerge from early May to early June. There is also the likelihood of moth migration during this period. Eggs are deposited on the leaves of grasses and corn plants. Larvae hatch about a week later and develop over a period of approximately 3 weeks. Fully frown larvae enter the soil to pupate. The pupal stage lasts about 15 days. New moths emerge in July. There are two and possibly a partial third generation larvae which reach their peak population during early June. Second generation larvae generally cause little damage. |
||||
| Damage | ||||
|
Armyworm damage is observed most frequently in no-till fields that were sod the previous year. The first symptoms will be ragged feeding on the top leaves with wet, brown, pellets in the area. The culprit usually can be found hiding well down in the whorl or at ground level under clumps of grass. Conventional-plated corn occasionally may be damaged by caterpillars that originate in a nearby small grain field prior to migration. When armyworms are numerous, small corn plants may be completely eaten. On very rare occasions, larvae of the second generation may attack corn in late July and August. These caterpillars hide under stones and clods during the day, then feed on grasses and lower corn leaves at night. However, the type of damage is much different than that caused by the first generation. They seldom destroy any leaves above the ear. |
||||
| Management | ||||
|
Corn fields likely to be attacked should be checked every few days during the first 2 weeks of June. Look for leaf feeding and presence of caterpillars in the whorl. Control action usually is not profitable unless 10 percent or more of the plants are infested. A number of insecticide sprays and baits can be used as a rescue treatment. Check the current issue of the Penn State Agronomy Guide for materials and dosage rates. You also may check with your county extension agent and local farm supply dealer for suggested controls. |
||||
| Warning | ||||
|
Authored
by: Stan Gesell, Extension Entomologist January 2002 ©
The Pennsylvania State University 2002
This publication is available in alternative media on request. Penn State is committed to affirmative action, equal opportunity, and the diversity of its workforce. Return to Entomological Notes Listing Home | Research | Extension
& Outreach | Graduate
Program | Courses | Personnel
|
||||
