2022 Pennsylvania Slug Monitoring Project

The PA Slug Project is back for its fifth year as part of the Soybean On-Farm Network, funded by the Pennsylvania Soybean Board. Penn State Extension educators throughout the state are beginning to monitor for slugs and will be regularly sharing in this newsletter their observations and the risk posed by slugs to no-till crop fields.

As planting gets started and progresses, be prepared for slugs if weather continues to be wet and cool. There are four slug species that can be encountered in in Pennsylvania field crops and are monitored in our project. See our Slugs as Pests of Field Crops fact sheet for more details. If you want to deploy slug traps on your farm, check out our Scouting for Slugs in Field Crops video.

Slug Management

Our research indicates that managing slugs requires an integrated pest management (IPM) approach that should be planned well before the spring planting season. The most diverse rotations tend to experience the fewest slugs and adding cover crops can increase rotational diversity. Our research is also showing that higher populations of ground beetles can help suppress slug populations. Populations of these beetle predators are reduced by insecticide use, including broadcast applications and insecticidal seed coatings.

We have a few tips to help manage slugs in the spring:

• Plant crops at the appropriate soil temperature to allow faster germination and seedling growth. Smaller seedlings with slow growth are more vulnerable to slug feeding damage.
• Ensure good furrow closure at planting. If the furrow isn't closed well, it can create a "slug highway" allowing slugs to easily feed on seeds and seedlings.
• Scout to determine if insecticides, including insecticide seed treatments, are necessary for your fields. Following IPM and only using insecticides if necessary will give our ground beetle predators a better chance to control slugs and other pests.
• Have some slug bait on hand for rescue treatments. If you are monitoring slugs and average 1-2 slugs per trap and there is severe slug feeding damage or dying seedlings, a slug bait is justified. Slug baits are most economical as a rescue treatment in portions of fields that are experiencing severe slug infestations. These baits can be ineffective, especially when it rains.

Week of June 7, 2022

This will be the last slug report for the spring. No slugs were observed at half of the locations. At the rest of the locations, very few marsh and gray garden slugs were reported. Damage continues to remain low and crops are steadily outgrowing any feeding damage.

• Adams – Heidi Reed
• Centre – Adriana Murillo-Williams
• Chester – Sarah Frame
• Columbia – Anna Hodgson
• Union – Anna Hodgson
• York – Heidi Reed

Week of May 31, 2022

There continues to be a mix of gray garden and marsh slugs observed. In the north, banded slugs have also been observed. All locations had an average of 1 slug per trap or less. No significant feeding damage was observed. Wolf spiders and ground beetles remain active across locations.

• Centre – Adriana Murillo-Williams
• Chester – Sarah Frame
• Potter – Nicole Santangelo and Jack Thomas
• Schuylkill – Dwane Miller
• Union – Anna Hodgson
• York – Heidi Reed

Week of May 24, 2022

One field had an increase in juvenile gray garden slugs with two of the traps averaging over ten slugs. Some eggs were also noted and indicate that the gray garden slugs recently hatched. Despite the increase in slug numbers, feeding damage in this field remained low and the crop is easily outgrowing the damage. The rest of the locations observed marsh and/or gray garden slugs at less than one per trap. No significant slug feeding damage was observed.

• Centre – Adriana Murillo-Williams
• Chester – Sarah Frame
• Columbia – Anna Hodgson
• Union – Anna Hodgson

Week of May 17, 2022

Some locations removed traps for the week for planting. Marsh and gray garden slugs are still observed in low numbers, less than one per shingle trap. One location reported a single dusky slug. As crops begin to emerge, we will begin scouting for slug feeding damage. Feeding damage remains low in reporting counties. Wolf spiders have been observed at most locations. Ground beetles were also common. 

• Bradford – Mason Tate
• Chester – Sarah Frame
• Potter – Nicole Santangelo and Jack Thomas
• Schuylkill – Dwane Miller  

Week of May 10, 2022

For this week, marsh and gray garden slugs were observed in low numbers. Marsh slugs were more common but averaged less than one per trap at all locations. Gray garden slugs were only observed in southeastern counties. Spider and ground beetle activity were noted at most of the field sites.

Reported counties for this week

• Adams – Heidi Reed
• Bradford – Mason Tate
• Centre – Adriana Murillo-Williams
• Chester – Sarah Frame
• Columbia – Anna Hodgson
• Montgomery – Andrew Frankenfield
• Union – Anna Hodgson
• York – Heidi Reed

Week of May 3, 2022

Of the reported fields so far, few slug eggs have been found. In each field, eggs were counted at ten random locations within a one square foot area and ten slug traps were installed. In all reporting counties, marsh slugs were most common but averaged less than one per trap. Gray garden slugs were observed less frequently with adults and slug eggs reported in the north and juveniles reported in southeastern PA. Banded slugs were reported at one location. Spider and ground beetle activity were noted at most of the field sites. Stay tuned for next week's report.

Reported counties for this week

• Columbia – Anna Hodgson
• Montgomery – Andrew Frankenfield
• Potter – Nicole Santangelo
• Union – Anna Hodgson
• York – Heidi Reed