Conducive Weather for Seedcorn Maggot & Slugs Outbreaks in Field Crops

The rainy and cloudy weather we are currently observing in many growing areas of Kentucky may lead to outbreaks of seedcorn maggots and slugs in corn and soybeans. These pests are problems on emerging seedlings and reduce plant densities. If outbreaks of either occur, damage may cause economic losses, and replanting will be necessary.

Favorable Conditions

Both seedcorn maggot and slugs are typically observed during cool and damp seasons. Seedcorn maggot prefers sites with organic rich soils (manure can be a source of this), including fields with reduced tillage or decaying residue from the previous season. Non-tillage, abundant residue from the previous growing season, and cover crops are also favorable for slug presence.

Figure 1. Seedcorn maggot. (Photo: Brenda Kennedy, UK).

Description & Habit

The seedcorn maggot is a larva of a small fly (Delia platura). It feeds on decaying organic matter and seeds of many plants, including many vegetables, corn and soybean seeds, and seedlings. The maggot has a yellowish-white coloration (Figure 1). These maggots are legless, about 1/4 inch (6 mm) long, cylindrical, narrow, and tapered. Maggots lack heads and legs but have small black mouth hooks in front.

Slugs affect earlier stages of soybeans (VE, VC, or V1), and these plants will not recover if the two cotyledons and apical bud are completely eaten. This damage may result in reduced planting density or produce empty spots in rows. Soybeans plants (V2 or older) are resilient and can support great amounts of foliage losses; plants will recover if there is partial feeding and leaves or stems were not completely damaged. In corn, if the apical meristem is not damaged, plants can recover from foliage damage caused by slugs.

Figure 2. Slugs and pearl-shaped eggs (arrow) in a field that has organic matter from the previous growing season (Photo: Raul Villanueva, UK)

Management

Although no reports have been made about damage caused by these two pests, the author has seen slugs in alfalfa and wheat fields. In these crops, damage caused by slugs is not noticeable as plant foliage is abundant; however, feeding by slugs might be happening and undetected. Field crop growers and consultants should be aware of this situation.

There are no rescue treatments for control of seedcorn maggot. Replanting is an option; however, the decision to replant should be based on plant population densities in the field, the date of occurrence, and yield expectation.

For slugs and snails, two products are registered for the control in corn and soybeans in Kentucky: Dealline™ M-PS Mini-Pellets (metaldehyde) and Sluggo™ (iron phosphate). Rates are shown on Table 1.

Table 1. Rates of Dealline™ M-PS Mini-Pellets (metaldehyde) and Sluggo™ (iron phosphate) for different stages of growth for corn, soybeans, and wheat.

By Raul T. Villanueva, Entomology Extension Specialist

Posted in Forages, Grains
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