Articles

Exploring the Value of Planting Green for Insect and Slug Control

Our study showed that delaying cover crop termination and planting crops into living cover crops (“planting green”) can increase predator populations, which then limit the abundance of insect and slug pests and reduce the need for pesticides.

Download Save for later Print

Updated:

December 15, 2025

Skip to the end of the images gallery

A recently planted “planting-green” plot; Jared Adam, Penn State

Skip to the beginning of the images gallery

Investigators

Jared Adam, M.S.
Dr. John Wallace, Ph.D., Department of Plant Science
John Tooker, Ph.D., Department of Entomology

Background

Traditionally, cover crops have been terminated 7–21 days prior to cash crop planting to conserve soil moisture and nutrients, break pest life cycles, and improve planting conditions. Delaying termination of cover crops to shortly after cash crop planting is an emerging practice known as “planting green.” Allowing cover crops to grow later into spring provides benefits, including increasing cover crop biomass, which can increase water retention, reduce soil erosion, improve soil quality, reduce nutrient losses, and decrease weed pressure. Based on previous research, we hypothesized that planting green could also improve populations of predators that could help control insect and slug pests.

Objective

We tested the potential of planting green to increase predator populations that could control insect and slug pests.

Methods

From 2021 to 2023, we conducted an experiment across three fields at the Penn State Russell E. Larson Agricultural Research Center (Centre County). Each field had four treatments (each replicated five times in each field):

1. No cover crop

Terminations of a cereal-rye cover crop:

2. 14–28 days pre-planting (“early terminated”)

3. 3–7 days pre-planting (“late terminated”)

4. 1–3 days after planting (“planting green”) of the cash crop

We planted glyphosate-tolerant corn hybrids without Bt traits and with no-seed-applied insecticides or fungicides; the soybeans were also glyphosate-tolerant and lacked seed-applied pesticides. We managed corn fertility by applying 40 lb of N at planting, with the balance sidedressed near the V5 to V6 corn growth stage. In the fields, we rotated corn with soybeans, using plots with the same footprints and experimental treatments each year. In each plot, we measured cover crop biomass, tracked slug populations, and quantified insect and slug damage to corn plants from emergence to growth stage V5. We also quantified predator populations and measured how much predation they imposed on sentinel caterpillars. At the end of the season, we measured crop yield.

Results

The three termination timings for our cover crop treatments established a gradient of cereal rye biomass present at planting. As expected, slug populations varied among years, with 2021 having the most slugs. In 2021, slug populations were highest in the planting green plots, but these plots did not receive significantly more slug damage on corn plants. Across the different cover crop treatments, the amount of damage to corn plants by different types of pests (e.g., slugs, black cutworm, armyworm, or stink bugs) was largely similar. For corn plants that were fed upon by more than one type of pest, we found more damage to corn in the planting green treatment. Overall, for plots that received cover crops, the amount of damage that corn plants received from pests was similar across treatments at the V3 growth stage, but at V5 planting green plots had significantly more plants injured by slugs (Figure 1), a difference that was not evident in yield results (see below).

Average slug damage score, on a scale from 0 to 4, is on a broken vertical axis due to averages around 0.2; the horizontal axis lists cover crop termination times: no cover, early termination, late termination, or planted green at two growth stages, namely, V3 and V5. No difference in damage scores is seen at the V3 measurement, but at V5, planted green soybeans had higher damage scores. — Figure 1. Average damage score for 2021–2023 in corn (mean ± standard error). Different letters indicate statistical differences (Early: 14–28 days pre-planting [DPP]; Late: 3–7 DPP; Green: 1–3 days after planting).

For predation, corn and soybean plots with cover crops consistently had more sentinel prey attacked by predators than the no-cover-crop control, but we found predator populations in our pitfall traps to be equal across treatments. Soybean plots consistently harbored more predators than corn plots. Notably, the predator populations in soybean plots were negatively associated with slug populations, suggesting that predators reduced slug populations in soybean. But, we found the opposite relationship in corn plots (Figure 2), indicating that predator populations in corn were insufficient to negatively influence slug populations.

For yield, in years 2021 and 2022, we recorded no differences in corn yield among treatments. In 2023, the no-cover-crop control had lower corn yields other three treatments. For soybeans, yields were equal across treatments in each year.

Scatterplot showing the relationship between slug population on the vertical axis and predator populations on the horizontal axis in corn and soybean fields under different cover-crop termination timings (no cover crop, early, late, green). — Figure 2. Relationships between slug and arthropod predator populations in corn and soybean. Corn is represented by the dashed line with hollow points that represent each treatment; soybean is represented by the solid line and filled points that represent each treatment (Early: 14–28 days pre-planting [DPP]; Late: 3–7 DPP; Green: 1–3 days after planting).

Conclusion

We found that greater amounts of cover crop biomass did not consistently lead to higher levels of damage to corn plants by invertebrate pests (i.e., insects and slugs). Our results in corn revealed some variability among treatments in herbivore populations and their damage, but damage did not exceed economic thresholds in any of the treatments and did not affect yield. For predation, we found no differences among treatments in corn, whereas in soybeans, the planting green treatment hosted greater amounts of predation than no-cover-crop plots. Moreover, soybeans hosted higher predator populations than corn, leading to lower slug populations in soybeans across all treatments. In summary, our results revealed that planting green can reduce pest abundance and their damage, in part by fostering higher populations of predators that can kill slug and insect pests.

Acknowledgments

Funding for this project came from USDA NIFA award 2019-68012-29818: Precision Sustainable Ag Coordinated Agricultural Project: A Cover Crop Network for Enhancing the Sustainability of US Cropping Systems.