Soybeans: Slugs

Excerpt from Agronomy Guide for Field Crops (Chapter 4)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Description
2. Life History
3. Damage
4. Scouting Techniques
5. Action Threshold
6. Management Strategies
7. Updates on Soybeans: Slugs
8. Related links...

Description

Juveniles and adults are soft-bodied, legless, greyish or mottled in appearance and have a slimy or gelatinous covering that helps keep them from drying out. The head has two pairs of tentacles. Slugs usually range from 1-3 cm in length but can reach up to 10 cm.

Life History

There is one generation per year but two populations, one maturing in spring and one maturing in fall. Therefore, both eggs and adults are found overwintering. Juvenile slugs hatch from eggs in the spring and the fall. They are active during cool and wet periods of the year. Slugs prefer environments with high humidity and relatively cool temperatures. Debris, such as crop litter or manure, provides them with shelter from the sun.

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Damage

Slugs feed above or below ground, depending on the moisture level. They can feed on germinating seeds and seedlings with no real preference for a plant part. On larger plants, slugs feed on lower parts, eating partly or completely through leaves, leaving ragged holes causing a skeletonized appearance on leaves. Feeding damage can resemble that caused by hail, and severe defoliation can result. The main concern with slugs on seedlings is that they often feed on the growing point, and the seedlings cannot recover from this. Damage occurs April through October under wet weather. Slug damage is most severe during prolonged cool, wet weather in May and June. Higher-risk fields include those where no-till practices on soybeans are used for a continuous period of time and those with considerable crop residue. No-till soybeans following forages or cover crop are also high risk.

Plate 54. Slug injury on seed. Slugs prefer high humidity, cool temperatures and debris to provide shelter from the sun.

Plate 55. Foliar damage caused by slugs. Slugs feed on all parts of the plant leaving ragged holes. Feeding on the growing point can kill the plant.

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Scouting Technique

Scout for slugs at night or in the early morning hours, when they are active (nocturnal). Look for stripping of leaf tissue and/or small holes chewed in the leaves. Check under debris and clumps of soil. A certain sign of slugs is a slimy, silver-coloured trail on the plants or soil. Check 1.5 m of row in five locations in the field (under clods and pieces of plant residue).

Action Threshold

Prevention is the only action available.

Management Strategies

Tillage can be used against slugs, since the elimination of the crop cover exposes the slugs to dehydration and predation by birds and mammals. Zone tillage or row sweepers can help speed up the drying of the row area, thus deterring slug feeding. Moving trash away from seedlings may help to reduce damage. There are presently no economical and effective chemical methods available for slug control. Refer to OMAFRA Publication 812, Field Crop Protection Guide, for any future chemical control options. (Order OMAFRA Publication 812)

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Updates on Soybeans: Slugs

• Field Crop Protection Guide - Publication 812
  • Soybeans: Slugs

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Related links...

• Insects
• Soybeans

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