Unlikely Visitor

Published online: Feb 08, 2020 Articles, Insecticide, Potato Storage Silvia I. Rondon & Rory J. McDonnell
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This article appears in the January 2020 issue of Potato Grower.

Many insect pests affect potatoes in the field and in storage. In the field, the green peach aphid, potato aphid, beet leafhopper, potato tuberworm, Colorado potato beetle and potato psyllid are among the primary pests in the Pacific Northwest. However, in storage, few insect pests are reported even though some have most likely been inadvertently moved into the storage units from the field.

In early fall 2017, samples of rotten tubers with slimy crawling creatures were brought to the Oregon State University Irrigated Agricultural Rondon Entomology Program (IAEP) in Hermiston, Ore. R.J. Mc Donnell, an OSU malacologist based in Corvallis, Ore., identified the creatures as gray field slugs, Deroceras reticulatum. This appears to be the first report in the U.S. of gray field slug infesting potatoes in storage, although there is another report in the literature coming from the Netherlands. This slug species is native to western Europe and is one of the most damaging slugs in the. They are polyphagous, meaning that they can feed in many crops, including wheat, corn, strawberries, ornamentals and several vegetable crops. The presence of this slug in Oregon seems to be an isolated case, since they prefer moist conditions, feeding at night or early morning and moving relatively fast, leaving a slime route behind.

When researchers were alerted to the presence of slugs in a commercial storage facility, they literally climbed the almost-four-story-high facility, and encountered slugs on walls and moving on top of tubers. Tubers were collected at random and placed in five-gallon buckets and brought back to the IAEP laboratories, where they were immediately inspected for the presence of slime, slugs per tuber (inside or outside), and feeding damage.

In addition, four groups of 50 tubers were placed in buckets and stored in the refrigerator at 8 degrees Celsius (about 46 degrees Fahrenheit) to evaluate the effect of cold temperatures on the biology of this slug species. The slugs’ preference for rotten versus healthy tubers was also examined. In general, low temperature seemed to slow them down but did not preclude them from moving, since almost all tubers presented slime. They did not appear to have a strong preference between a healthy or rotten potato, but they could considerably damage healthy potatoes with their strong teeth.

This is the first report of slugs being found in a potato storage facility in the U.S. and hopefully the only one; however, the potato industry should be aware of the presence of this creature and the potential damage it can cause. For additional information on this discovery, check out the author’s paper that was recently published in the American Journal of Potato Research.


Silvia I. Rondon is a professor and extension entomologist at Oregon State University’s Hermiston Agricultural Research and Extension Center. She can be contacted at silvia.rondon@oregonstate.edu.

Rory J. McDonnell is a professor with OSU’s Department of Crop and Soil Science and is based in Corvallis, Ore. He can be reached at rory.mcdonnell@oregonstate.edu.