Conservation Tillage Increases Beneficial Insects in Peanut Fields

What is conservation tillage?

Conservation tillage refers to soil cultivation with direct drilling (no tillage) and minimum tillage. Conservation tillage is often used in conjunction with cover crops to allow surface incorporation of crop residues. Conservation tillage maintains a minimum of 30% of the soil surface covered by residue after drilling. Oppositely, conventional systems of tillage leave less than 30% of crop residues, and often none, on the soil surface after crop establishment. Conservation tillage conserves soil moisture, reduces run-off, increases the surface soil organic matter, reduces soil erosion and water contamination. Conservation tillage has been promoted in the US because it provides substantial environmental benefits, including reduction of soil erosion. This has become more important with climate change that is exacerbating the problem of soil erosion with erratic rainfall events and greater frequency of storms.

What are the effects of conservation tillage on beneficial insects?

Conservation tillage along with cover crops helps promote year-round natural enemy populations by providing alternate prey, reproductive sites, and protection from adverse conditions. Conservation tillage increases grass weeds and retains organic matter, leading to an increase of detritus feeding species upon which beneficial predators depend.

Conservation tillage can also reduce the environmental impact of insecticides by modifying the soil structure and affecting the degradation of insecticides in the soil. The fate of insecticide following application depend of many factors including insecticide’s active ingredient and adjuvants, environmental conditions, and soil properties. Insecticides may cause severe or chronic effects on beneficial organisms before they are degraded into harmless compounds.

A recent study conducted in peanuts at the North Florida Research and Education Center in Quincy demonstrated that predators of soil pests were protected by conservation tillage. The experiment consisted in a peanut field planted after a cover crop of oats. The field was divided into areas with conservation or conventional tillage. The peanut field was then treated with different types of insecticides. Soil pests found in the peanut field included mole crickets, click beetles, and peanut burrowing bugs, whereas soil pest predators included earwigs and ground beetles. Both soil pests and predators increased significantly under conservation tillage (Fig. 1). However, the application of insecticides on conventional tillage, such as imidacloprid, decreased significantly the number of soil pests as well as the number of predators.

Fig. 1: Increased of natural enemies in peanut soil, under conservation tillage vs conventional tillage.

Interestingly, under conservation tillage the number of soil pests also decreased following insecticide application, but the predator populations remained at the same level as in the untreated area. The conclusion of this study was that conservation tillage increased significantly the number of soil pest predators and potentially protected them against the non-target effect of insecticides. Therefore, conservation of natural enemy population can be added to the numerous advantages of conservation tillage in peanuts.