Developing an IPM program against slugs in mid-Atlantic no-till grain fields

Developing an IPM program against slugs in mid-Atlantic no-till grain fields

Summary

Since their introduction in 1991, neonicotinoids have quickly become the most popular insecticides worldwide. Within the past decade their use as preventative seed coatings has expanded enormously and now hundreds of millions of acres of field crops are planted annually with neonicotinoid seed treatments (NSTs). Unfortunately, the great majority of NSTs are used outside an IPM framework with little regard for pest populations even though limited unbiased evidence suggests that NSTs improve yield and profitability. Moreover, recent evidence suggests that they can pollute surface water and negatively influence wildlife, including populations of pollinators. In addition, our ongoing research is documenting that NSTs are exacerbating slug populations in no-till crop fields by disrupting biological control. This issue is important because slugs are among of the most challenging crop pests faced by Mid-Atlantic and Northeastern field crop growers. To combat slug infestations and over-reliance on NSTs, we are collaborating with four farmers in central Pennsylvania to test an alternative approach that avoids NSTs and uses rye cover crops to provide an alternative food source for slugs while maintaining strong populations of potential predators.  

We finished the field part of the project in November when we harvested the corn in the four farms. Some of the data (slug damage, corn productivity, and yield) have already been analyzed while others are still a work in progress (e.g. identification of natural enemies). Preliminary results indicate that the rye cover crop reduced slug abundance and damage to the subsequent corn crop, while the influence of neonicotinoids was more subtle.

Objectives/Performance Targets

Our two specific objectives were to:

1. Determine the influence of a fall-established rye cover crop on slug and natural enemy populations and slug damage to corn;
2. Compare corn productivity and biological control of slugs in presence and absence of neonicotinoid seed treatments.

 On four farms of members of the Pennsylvania No-Till Alliance, we established a factorial experiment crossing two levels of seed treatment (treated or untreated seed) with three levels of cover: bare plot, rye cover crop terminated before planting, rye cover crop terminated after planting = “green”.

Accomplishments/Milestones

Fall 2014

November

Plant rye in assigned plots (four growers)

Order corn for the four farms (Mr. Anchor)

Spring 2015

May

Terminate rye two weeks before planting corn (four growers)

Plant corn (four growers)

Terminate rye 5 days following planting corn (Mr. Harbach, Mr. Anchor, and Mr. Criswell).

Summer 2015

June through August

Measure slug populations (shingle traps) and scout for early pest every other week (Dr. Le Gall)

-We actually increased the sampling effort and sampled weekly.

June

Collect pitfall trap samples (Dr. Le Gall)

Deploy pinned sentinel waxworm caterpillars (six per plot) for three hours during the early morning, and then again in the early evening (Dr. Le Gall)

-Because of logistical constraints, we only checked the sentinel prey once, after leaving them 24h in the field

Assess cover crop/crop residue per plot (i.e., percent cover) using the line-transect method (Dr. Le Gall)

Corn V5 stage. Assess stand establishment by counting the number of plants in four randomly chosen 10-ft sections of row and measure slug damages (Dr. Le Gall)

July

Collect pitfall trap samples (Dr. Le Gall)

Deploy pinned sentinel waxworm caterpillars (six per plot) for 24h (Dr. Le Gall)

August

Collect pitfall trap samples (Dr Le Gall)

Deploy pinned sentinel waxworm caterpillars (six per plot) for 24h (Dr. Le Gall)

-We only made this effort on the two farms were slugs were actually observed (i.e. Anchor and Criswell)

Fall 2015

September 2015

Schrack farm field day (Dr Tooker and Dr Le Gall), 60 attendees

Anchor farm field day (Dr Tooker), 50 attendees

October 2015

Harvest corn and measure yield (four growers)

-Actually harvested in November

Impacts and Contributions/Outcomes

Overall two farms had heavy slug infestation, Criswell and Anchor farms. Very few slugs were observed at Meyer and Schrack farms.

1) Corn damage (June 2015)

There was less damage by slugs in the planting green treatment. The effect is particularly true at the Criswell farm where 49% of the plants were damaged by slugs when the rye was killed prior to planting, while only 19% were when the rye was killed after planting. Interestingly, the level of damage in planting green (20%) is similar/lower than the levels observed in farms where there was no heavy slug infestation (Meyer and Schrack farms).

2) Pitfall sampling (monthly June, July, and August)

Ants

There was more ants observed in the green cover crop treatment both at Schrack and Meyer farms.

Slugs

Less slugs were counted in the pitfall samples when the rye was killed after planting the corn. Again this effect is very noticeable at Criswell farm.

Yield data

There was no differences in yield at Criswell’s farm and Meyer’s farm. However the yield was smaller for the green treatment at Anchor’s farm (about 12% less). 

Neonicotinoids

At the Anchor and Criswell farms corn establishment appeared lower for the non-treated plants. We counted on average 18.8 plants on a 10 ft portion of a row when the seeds were treated and 17.8 plants when they were not. Interestingly, this did not resulted in lower yields for either farms. However more analysis will be needed to explain this discrepancy between the lower number of plants yet equivalent yields. It is possible that higher natural enemy populations in the non-treated plots can explain why yield are similar. Higher natural enemy populations could limit damage and increase corn productivity in field that are not treated with neonicotinoid seed treatments.

Collaborators: