Figure 1. Deroceras reticulatum, the "grey field slug", on wheat growing near
Crooked Creek AB (August 2, 2018; det. Lien Luong).
Figure 2. Flag leaf feeding damage on wheat caused by the grey field slug (Deroceras reticulatum).
Photo taken near Crooked Creek AB on August 2, 2018, by J. Otani.
Field scouting was performed in the evening from 8:30-10:30pm. As the temperatures decreased, the slugs moved up the wheat stems, climbing to the topside of the flag leaf and onto the wheat heads although they did not appear to feed at the developing kernels. Wheat was hand-collected by clipping stems ~20cm above the ground to later reveal a density of 1.04 slugs per stem (n=465 stems) causing the above damage (Fig. 2).
Specimens were forwarded to L. Luong (U of A) who identified the slugs from the above field as one species, Deroceras reticulatum, the grey field slug. The majority were juveniles. The grey field slug is the most common to occur in the home garden.
Thanks to Dr. John Gavloski (Manitoba Agriculture) who prepared the following in relation to slugs in field crops:
- Slugs are a complicated problem because most general insecticides don’t work well on them.
- Sluggo Professional (PCP#30025) is registered for slugs in field crops. It is a bait, which must be consumed by the slugs to be effective but it could be expensive on a large field.
- Often insecticides don't work well on slugs and it may be related to the mucous coating slugs exude.
- Be wary, if an insecticide is applied, the product will likely not affect the slugs but it will kill the ground beetles and other natural enemies that prey upon or parasitize slugs and could exacerbate the slug problem.
- Growers using no-till or minimum till operations may consider tillage to help reduce future levels of slugs.
Health Canada has an overview of snails relating to gardening posted here.