Wednesday, May 21, 2008

Nursery, Landscape, and Greenhouse - Wet Weather Means Slugs

Wet weather has increased slug activity in landscapes. The following is information on these pests and their control from the University of Maryland.

In wet seasons slugs and snails, invertebrates with soft bodies in the phylum mollusca, can cause major losses of plants or a reduction in the quality of plant material in nurseries and can damage plants in the landscape. The high humidity environment of production beds is well-suited for supporting populations of slugs and snails. Several native and imported slugs and snails have been reported damaging foliage of annuals and herbaceous perennial plants.

Damage to Monitor

Plant damage occurs by the rasping action of the mouthparts. Damage to leaves appears as irregularly shaped holes with smooth edges. They can chew off succulent plant parts and growing tips that are close to the ground. Seedling plants can be completely consumed. A slime trail is nearly always associated with fresh feeding injury.


Metaldehyde baits have been shown to attract slugs up to 3 feet away. The toxic effects of metaldehyde seem to be primarily due to dehydration as it elicits excessive mucus production (mucus is 98% water and 2% mucoproteins.) Thus in dry weather, metaldehyde is more effective. In wet weather, slugs sometimes can absorb enough moisture to compensate for the water lost in mucus production and therefore recover from the effects of metaldehyde. However, if slugs consume too much metaldehyde, they do not recover. Slugs seem to become more susceptible to carbamate pesticides as they mature. Copper sulfate is toxic to slugs and slugs will not crawl across a barrier of copper metal or wooden surfaces treated with copper sulfate. Mesurol is labeled for slug and snail control in greenhouses, and it also kills thrips. The problem is that Mesurol has a 24 hour REI.

Reprinted from the May 9, 2008 edition of the Greenhouse TPM/IPM Weekly Report from the
University of Maryland Cooperative Extension

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