Wallaces Farmer

Minimize risk to corn seedlings this springMinimize risk to corn seedlings this spring

Corn Source: Soil-applied insecticides can help reduce seed death or seedling injury from early-season corn insects. Scouting after planting can help evaluate replanting options.

February 5, 2025

4 Min Read
(top left) seedcorn maggot larvae, (bottom left) wireworm larvae and (right) white grub
TERRIBLE TRIO: Three insects can inflict early-season damage on corn seeds and seedlings. They include seedcorn maggot larvae (top left) (photo by Jim Kalisch), wireworm larvae (bottom left) and white grub (right) (photos by Ashley Dean).Photos by Jim Kalisch and Ashley Dean

By Ashley Dean and Erin Hodgson

As spring field activities resume, it is wise to think about early-season insects and how different crop production decisions might affect seed or seedling injury risk. Scouting for pests that cause seed and seedling injury can be tricky because they feed under the soil surface.

Unfortunately, rescue treatments in the form of foliar insecticides are ineffective for belowground pests such as seedcorn maggot, wireworms and white grubs. Understanding the risk is important to help reduce potential losses.

Scout before planting

The best way to mitigate risk is to scout for seedling pests before planting. If scouting reveals the presence of one or more pests, there are two options for the current and future growing seasons:

  1. Delay planting until soils warm and dry up. Vigorous plant growth is an effective strategy to mitigate potential losses.

  2. Use a soil-applied insecticide to reduce seed death or seedling injury.

After planting, scouting for early-season insect pests can be easily combined with stand assessments. Most of the pests described below are localized within fields and tend to be problematic for several years. Dig within a row of suspected plants with injury to confirm the presence of a pest. Be sure to distinguish feeding injury from soil compaction and plant diseases.

Related:Why 105-day corn doesn’t mature in mid-August

If significant stand loss occurs, fields or portions of the field may need to be replanted. Consult a corn replant decision guide to help determine if replanting is necessary. Injury by belowground pests tends to be worsened when corn grows slowly in cool soils, and wet soil conditions increase secondary infections of pathogens.

Seedcorn maggots

Corn injured by seedcorn maggot can have a wide range of symptoms. White, legless larvae burrow into the seed and consume the embryo, which can cause plant death before germination or weak seedlings.

The most obvious sign of injury is reduced stand or gaps in the row. Check field areas with stand loss for maggots, damaged seeds or poorly developed seedlings. Infestations of seedcorn maggot tend to be throughout the field.

There are no rescue treatments for seedcorn maggot, so the focus should be on minimizing the risk of infestation and planting during the fly-free period. (Track development using the Pest Maps and Forecasting page on the Iowa Environmental Mesonet website).

Egg-laying females are highly attracted to fields that recently have been tilled or have high organic matter, such as recently incorporated manure, cover crops or weeds. There may be up to five generations of seedcorn maggot each year.

Related:What you should know about corn stunt

Wireworms

Wireworms are the larvae of click beetles. They typically are orange in color, slender and segmented. Similar to seedcorn maggot, wireworms feed on the embryo and often hollow out seeds. They also may feed on the developing root or tunnel into the stem belowground.

The most obvious sign of injury is gaps in the row, but less severe feeding appears as stunted or wilted plants. Wireworms are more likely to be found in well-drained soils on ridgetops or hillsides.

There are no rescue treatments for wireworms. This pest has an extended life cycle, where larvae may live in the soil for six to seven years before becoming adults. This may lead to persistent issues in some fields. Females tend to lay eggs near the roots of grasses, so crop fields recently transitioned from sod, CRP or pasture are likely to have issues with wireworms.

White grubs

Several grub species may be present in crop fields. These include true white grubs, such as May and June beetles. They also include annual grubs, such as the Japanese beetle. All species look similar: C-shaped and white with a brown head capsule. Distinguishing between species requires looking at patterns of hairs on the tip of the abdomen, which is a difficult task. However, it might be worthwhile if there is a persistent issue.

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True white grubs have a three-year life cycle, meaning larvae can feed for three years in the soil before becoming adults. Annual white grubs complete one generation per year and may be less persistent.

White grubs feed on the fine root hairs of grasses and some field crops, reducing nutrient and water uptake. Aboveground symptoms include wilting, purple leaves and stems, and occasionally stand losses.

There are no rescue treatments for white grubs, so scout fields before planting to determine risk. Fields that were previously in sod, pasture or CRP are at the highest risk for grub injury, but fields adjacent to permanent grass, cottonwood trees or willow trees also may have significant injury.

Dean is an Iowa State University Extension education specialist for field crop entomology. Hodgson is an ISU Extension entomologist.

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