As slugs consume crops across Pennsylvania and though diligent research and observation, entomologist Dr. John Tooker has found the source of the problem to be the very thing designed to control pests on crops.
Dr. Tooker presented a talk March 4 in the FedEx Institute of technology explaining his findings on how the mass use of neonicotinoid pesticides, or neonics, has caused a growth in slug populations on crops, decreasing the farms’ yields. Dr. Tooker is an entomologist, but describes himself as an insect ecologist, studying the roles insects play in the environment. To understand what is happening in Pennsylvania, some background is needed about the environment modern farms exist in.
Pennsylvania uses no-till farming throughout the state, a method also used across Tennessee, in which farms are not plowed between seasons, leaving natural debris throughout the farm. This is beneficial in preventing soil erosion, decreasing labor costs and conserving soil and water throughout the year. This way of farming is much more conservational than traditional means, providing less waste of resources and more capital to spend on equipment and pesticides.
Across the country, plant seeds are treated with neonic pesticides, coating the seed before it is planted. The insecticide is then brought up through the plant as it grows, protecting them from preying herbivore insects. However, slugs are mollusks, meaning the insecticide has no damaging effect on the slug, leaving them free to eat as much as they can.
The slugs eventually become carriers of the insecticide and pass it on to predators such as ground beetles. These predators are then killed by the insecticide, causing a drop in the predator population among the crops, causing the slug population to rise and reduce the crop yield in the farms.
Another issue arises with the farm’s decomposers. The debris left by practicing no-till farming is the ideal environment for slugs to live, meaning that steady decomposition of this debris is key in managing the slug population. However, the insecticide kills a portion of decomposers as well, and when studied, it was discovered that there is a 10% reduction in decomposition when comparing treated crops to non-treated crops.
This one-two punch is what has been driving the slug population up. By introducing the neonic insecticide to the environment, farmers are inadvertently interrupting the natural flow of prey-predator relations, killing the needed predators, and preserving the harmful prey.
The insecticide also preserves the slug’s living environment, which motivates some farmers to abandon no-till farming altogether to ensure crop yields are not affected by pests living in the debris.
With this information, Dr. Tooker began researching how crops treated with the neonic insecticide compared to those which were not, comparing the general slug population among each one. What Tooker's research found was that among the plants treated with the insecticide, there was a greater number of slugs, causing the opposite reaction of what farmers would hope. The question then became how farmers could manage pests without the use of the insecticides.
The answer is integrated pest management, or IPM. By integrating different crops and ensuring a stronger predator population, farmers can greatly control the populations of pests feeding on their crops. IPM is accomplished by intercropping and was tested on a larger scale on one farm in Pennsylvania.
The Pennsylvania farm planted rows of cereal rye between rows of soybeans, a major cash crop of Pennsylvania. What was observed was that the slugs favored the cereal rye over the soybeans, cutting the damage done to the soybean crops in half.
In addition to this, the ground beetle population was found to have tripled among the cereal rye, increasing the pest predators in the environment, and increasing the crop yield for the farm.
While this is great news, Dr. Tooker is quick to point out that this is not an end-all solution. IPM is much more management intensive, requiring more work and cost on the part of the farmers. It is also not applicable for large farms, like those across the Midwest, for being too expensive to do across such a large area. However, Dr. Tooker’s research provides hope for the future of conservation-minded farmers and ecologists, fueling new ideas for those who learn from him.
One student already had new ideas when leaving the talk.
“I like the idea of how you grow crops in between the plants to distract the slugs, and how slugs really liked canola plants,” said biology student Emma Caufield. “So, now I wonder if you committed a quarter of your patch to canola, and would they leave the other part alone then? It makes me want to try it.”
