Many insects are likely to call corn fields their home throughout the growing season. Some of these can be beneficial while others can harm your crop. Proper identification and management is a key for maximizing yield potential. Scouting fields early and often is the first step in implementing a successful management program. While scouting, it is important to note any insect activity. Insects may be feeding on the seed, roots or shoots. Three insect larvae are of importance to germinating seed and seedlings: seedcorn maggots, white grubs and black cutworms.
Seedcorn maggots can be found on every continent except Antarctica. Feeding and damage is generally more severe in years with cool, wet springs. The larvae are yellowish-white in color (Figure 1), are about 0.25 of an inch in length, have a pointed head end, and are legless with tough skin. As an adult, they are a grey-brown fly that is about 1/3 of an inch long.
White grubs (Figure 2) are broadly found across North America and can damage or kill corn seedlings by pruning roots and feeding on the mesocotyl. The most common white grub species in corn fields are annual, Japanese and true white grubs (Figure 3,4). The respective adults are the masked chafer, Japanese beetle and the May or June beetle. The larvae are creamy white, C-shaped and can be up to 1 inch long. They have six prominent legs on the fore end and the hind part of the body is smooth and dark. True white grubs, identified by a zipper-like row of hairs on the tail, are usually the most destructive because they remain in the larval or grub form for three years. Therefore, a field infested the prior year with true white grubs is likely to be infested the next year unless they are managed with a soil-applied insecticide. The true white grub adult is brown to brownish-black and emerges from May to June.
Black cutworms can be found throughout most of North America and are the most economically relevant species of cutworms (Figure 5). Black cutworm larvae can be up to 2 inches, vary in color from light gray to black, have granular-appearing skin and are most easily identified by the pair of dark tubercles found on each body segment.
Symptoms of injury
Besides these three insects, there are several other insects that may be of concern in your area. Depending on your location and field conditions, other common early season insects may include wireworm, chinch bug, flea beetle, green stinkbug, billbug and grape colaspis. Your Channel Seedsman can assist you in identifying which insects may be causing issues in your field.
It is important to stay ahead of pests, and fields should be scouted on a regular basis to determine which insect pests are present. Treatment thresholds vary by state, pest, and stage of crop development. Consult your state’s extension entomology resources and/or your Channel Seedsman for local recommendations. If a threshold is met and a rescue treatment is recommended, the appropriate insecticide should be applied promptly and per label directions.