Using Integrated Pest Management to Balance Soil Health and Insect Management

Farmers in the United States have expressed increasing interest in soil health. Soil health is a generalized concept based on improving soil quality and the idea that soils containing a diversity of life will produce more vigorous plants capable of resisting insect pests or pathogens. This diversity of life generally includes microbes and worms, but also comprises beneficial arthropods, which include insects and related animals that can be predators (e.g., beetles, spiders) or decomposers (e.g., springtails, mites, millipedes). Soil health is being promoted by USDA Natural Resource Conservation Service, local conversation districts, and extension personnel. As a result, many farmers are adopting soil-health practices on their farms to try to build biological diversity and function in their soils. Soil-health practices typically involve no-till farming and using diverse rotations that include cover crops.

It should be noted, however, that many of the same farmers who are interested in soil health typically continue to farm using common preventative pest management tools, including seed coatings that include insecticides and fungicides or pre-emergent or post-emergent broadcast applications of insecticides and fungicides. There is a common belief that these sorts of pesticide uses are vital to crop production, but sufficient research has demonstrated that this is not the case. Many of the pest species being targeted by these pesticide applications can be difficult to find, and yield responses are inconsistent when these pesticides are used. Further, undirected insecticide use can limit populations of beneficial arthropods that are important contributors to decomposition and pest control (Figure 1), particularly for hard to control pests like slugs. Similarly, crop fields tend to benefit from populations of beneficial fungi that can facilitate nutrient uptake or contribute to decomposition, and regular use of fungicides can limit contributions of these fungi.

From a soil-health perspective, it is worth noting that pesticides, which are used to kill various organisms, have the potential to limit the very life in soil that soil-health practitioners are trying to build. So curious minds want to know: "what do insecticides and fungicides do to soil health or quality?" The answer to this question is unknown, but learning the answer is the goal of some relatively recent, ongoing research at Penn State. Using research funds from the U.S. Department of Agriculture, members of the Tooker Lab in the Department of Entomology at Penn State are collaborating with colleagues in the Department of Entomology at Cornell University to understand whether insecticides and fungicides alter soil quality. Moreover, if they do alter soil quality, what do they do? Over the course of three years, our research is quantitatively assessing the influence of pest management tactics on soil quality (Figure 2). In Pennsylvania in a corn-soybean rotation that includes cover crops or not, we have different treatments that vary the intensity of pest management, while in New York we are applying similar varying pest management treatment to a corn-soybean rotation that was preceded by perennial hay. In our research plots, we are sampling arthropod populations, including both pests and natural enemies, and fungal populations. We are also sampling soil a few times a year to assess soil quality and quantify biological function with a variety of tests.

We are currently in the process of planting the third season of this project and will be collecting data throughout the 2019 growing season. We expect the effects of pest management to accumulate over the years and be the strongest after year three. Thus far, some of our results suggest that where insecticides and fungicides are used consistently, populations of arthropod predators tend to lower, and microbial decomposition (Figure 3) tends to be slower, than in plots were insecticides and fungicides were not used. Similarly, we have found that populations of beneficial fungi that can kill plant-feeding insect pests tend to be lower where fungicides are used regularly. These are an incomplete view of some of our results that align with our hypotheses, but we will learn more as we continue to collect data and analyze the results. Some of our more interesting results are yet to come and may involve how soil function changes over time with the contrasting influences of pesticide exposure and soil health practices.

We are uncertain what the final results of this research will show, but the outcome will provide insight on how to integrate pest management needs with the goals of building soil life via soil health practices. We expect that using insecticides and fungicides judiciously via Integrated Pest Management will provide the best balance of controlling pests while preserving soil life to help improve soil quality. When we approach the end of our project, we will do our best to share the results through this newsletter and via talks at various Penn State Extension meetings. 

Figure 2. Our research team sampling soil prior to planting. Periodic soil sampling is allowing us to quantify changes to soil quality over time in response to soil health practices and pesticide use.  Photo by Elizabeth Rowen, Dept. of Entomology, Penn State.

Figure 3. Bait lamina strips used to measure microbial decomposition in our experiments. We fill the holes in these plastic stakes with a cellulose-based paste and then place the stakes in the ground. The number of holes without paste after a field season is a measure of the microbial activity in our plots. Photo by Elizabeth Rowen, Dept. of Entomology, Penn State.