Effects of Living Mulch and Cover Crop Residues on Natural Enemy Abundance and Efficacy in Sweet Corn

Progress report for GNE19-224

Project Type: Graduate Student
Funds awarded in 2019: $14,009.00
Projected End Date: 09/30/2021
Grant Recipient: University of Maryland, College Park
Region: Northeast
State: Maryland
Graduate Student:
Faculty Advisor:
Dr. Cerruti R. R. Hooks
University of Maryland
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Project Information

Summary:

This project will be conducted over the upcoming 2020 growing season and will address the need for non-chemical insect pest control methods in sweet corn production by investigating the potential for cover crop residues and living mulches to increase insect natural enemy abundance, consequently reducing pest numbers and associated crop damage. Visual assessments, sticky cards and pitfall traps will be used to determine the diversity of natural enemies present, and sentinel corn borer and earworm egg masses will be placed in the field and assessed for predation/parasitism. Additionally, corn earworm pre-pupae will be tethered and exposed to ground predators in all treatments to determine predation mortality. Crop damage and overall yield will also be assessed in each treatment. Results will be presented at on-farm tour events, extension meetings throughout the following fall/winter season and at at least one scientific conference. The impacts on the agricultural community are currently unknown, and will depending on the results obtained this summer. 

Project Objectives:

The overarching project goal is to improve the biological control services provided by ground and foliar inhabiting natural enemies in sweet corn plantings.

My primary research objectives are to assess the effects of growing sweet corn with an interplanted living mulch and cover crop residues on:

1) the number of foliar and epigeal (ground) natural enemies present,
2) rates of predation and/or parasitism of corn earworm and European corn borer egg masses,
3) rates of corn earworm, sap beetle, and stink bug damage
4) crop yield.

Introduction:

The purpose of this project is to investigate the ability of cover crop residues and living mulch to enhance natural enemy abundance to suppress the corn earworm and the European corn borer and reduce ear damage. More specifically, I will investigate effects of red clover living mulch and crimson clover/rye residues on predation and parasitism of the immature stages of the corn earworm and European corn borer, and examine treatment impact on corn earworm adult emergence.

The corn earworm is a polyphagous lepidopteran pest of several field and vegetable crops, and is one of the most devastating and difficult to control insect pests in the United States. Up to 50% losses in sweet corn have been reported as a result of this pest. The European corn borer, though largely controlled in many areas of the United States with genetically modified (GMO) corn varieties, still has the potential to cause significant damage to non-GMO sweet corn cultivars. Thus, organic farmers and others not using GMO sweet corn must depend primarily on insecticide sprays. However, resistance problems may reduce the period that insecticides and GMO cultivars are effective. Additionally, both pests are difficult to control via foliar insecticides due to the short period of vulnerability before they are protected inside the corn plant. This suggests that growers, especially organic producers, can benefit from more sustainable management options.

Living mulches, which are cover crops grown alongside the main crop throughout the growing season, and cover crop residues are increasingly used to suppress weeds in agricultural production. However, limited research has been conducted to evaluate their impact on insects and other arthropods in specialty crops. Previous research investigating the impact of no-till production on corn earworm prepupal search behavior and subsequent site selection for pupation indicates a preference for loose, tilled soils over smooth, compacted surfaces associated with no-till production. Studies determined H. zea pupae spent a significantly greater amount of time and traveled greater distances searching for a suitable pupation location in no-till compared to conventionally tilled fields. This increased search time extends the period that larvae are vulnerable to predation by ground-dwelling arthropods, many of which are more abundant in more diverse habitats. This suggests that integrating cover crops into sweet corn systems should result in greater pre-pupal predation and a subsequent reduction in H. zea adult emergence. This could have important consequences on numbers of adult moths dispersing to other crops later in the growing season.

Foliar searching natural enemies may be greater in living mulch systems, often resulting in reduced insect pest populations. Thus increased mortality due to natural enemies could occur in the foliage and at soil level. However, few studies have investigated the impact of habitat diversification on H. zea infestation rates in sweet corn; and to my knowledge, no studies have examined impacts of cover crop residues on H. zea or O. nubilalis mortality from natural enemies; and how this affects ear damage and yield. Thus, this project will contribute to the sparse body of knowledge related to the impact of habitat diversification on economically important sweet corn pests and provide growers a more sustainable and environmentally friendly option.

Research

Materials and methods:

Cover crop treatments were established in early September 2019. The four treatments are: NT (no till), CT (conventional till), LMFR (living mulch + forage radish) and LMRye (living mulch + rye). In the NT and CT treatments, a mixture of crimson clover, forage radish and rye cover crops were planted. In the LMFR treatment, alternating rows of red clover and forage radish were planted, and in the LMRye treatment, alternating rows of red clover and rye were planted. All cover crops were planted on September 5, 2020 at 6 inch row spacing. Additional overhead irrigation was required after ~ 2 weeks due to excessively dry conditions. In Spring, (Mary 25, 2020) when the cereal rye reached anthesis, the cover crops were terminated. The NT treatment was terminated using a roller to create a thick barrier of cover crop residue. The CT treatment was mowed and disked to create a bare ground control treatment. The LMFR and LMRye treatments were rolled to terminate any remaining forage radish as well as the cereal rye respectively. Immediately following cover crop termination, sweet corn (variety: Providence) was planted in each treatment at 30 inch row spacing, resulting in sweet corn rows centered between the rows of red clover living mulch in the LMFR and LMRye treatments. 

Beginning four weeks after planting, pest and beneficial insects were monitored via visual counts, yellow sticky cards and pitfall traps. Weekly visual counts were performed by visually inspecting the entire surface of twenty corn plants per plot and recording any pest or beneficial insects present. To assess aerial insects within each treatment, two yellow sticks cards  per plot were set during four sweet corn growth stages (V5, V13, R1, R3) and remained in the field for one week. Finally, to assess epigeal insect communities, four pitfall traps were plot were set up such that two traps were within the sweet corn row and two were between sweet corn rows, in the red clover in LMFR and LMRye treatment plots. Two sampling dates corresponding to the V9 and R2 sweet corn stages were planned. However, due to heavy rains, pitfall trap catches were lost for the second date, resulting in pitfall samples from only the V9 growth stage. 

To assess treatment effects on rates of pest predation and/or parasitism, ten corn earmworm and ten European corn borer egg masses per plot were deployed weekly beginning in mid-June. Using insect pins, European corn borer egg masses were attached to the undersurface of a leaf, while corn earworm eggs were attached to the husk tip around the corn silk. Egg masses were collected after three days, evaluated for predation, then placed in gel caps and monitored for parasitoid emergence. An experiment testing predation of earworm prepupae was planned. However, preliminary experiments performed during the summer of 2019 suggested that predation data was inconsistent and unreliable. As such, this experiment was eliminated. Insect ground predator data was, however, gathered via pitfall traps, and any impacts on prepupae survival would result in differences in adult earworm emergence, monitored using emergence cages after harvest. 

Because this study exists within a larger weed management experiment, treatment plots were divided into two subplots, one which received an at-planting application of residual herbicide and the other which did not. Herbicide application is assumed to have no effect on insect data collected for this experiment since the application occurred before sweet corn seed germination. However, impacts on crop yield are possible. Therefore, yield data was collected and analyzed separately for each subplot. All marketable ears were harvested from the center 6.1 meters of the center four rows of each subplot, weighed, and rated for corn earworm, sap beetle and stink bug damage. Earworm damage was measured as square centimeters of damage per ear. Sap beetle and stink bug damage was measured as number of damaged kernels. 

Research results and discussion:

Similar numbers of marketable sweet corn ears were harvested from all subplots, resulting in no significant differences in yield between any whole-plot or sub-plot treatment (Figure 1). 

Figure 1. Total number of marketable sweet corn ears harvested from each subplot. There was no effect of whole-plot or sub-plot treatment on sweet corn yield.
Figure 2. Average corn earworm damage per harvested ear within each treatment. Ears in the CT control treatment had significantly less damage than harvested ears in the NT treatment (. Damage in both living mulch treatments (LMFR and LMRye) was not significantly different from any other treatment.

Corn earworm, sap beetle and stink bug damage were recorded at harvest for all marketable ears. Overall, significantly more earworm damage  occurred in the NT treatment compared to the CT control treatment. The two living mulch treatments, LMRye and LMFR, were not significantly different from any other treatment. There were no significant differences in sap beetle or stink bug damage between treatments. 

Sample processing and data analysis are still in-progress for pitfall trap, sticky card, sentinel egg mass and emergence cage samples. 

Research conclusions:

Conclusions can be drawn only for treatment impacts on harvest damage and crop yield. Growing sweet corn in combination with red clover living mulch does not result in any reduction in marketable yield or pest damage. As such, there appear at the time to be no direct drawbacks or benefits to this system. However, differences in pitfall trap and sticky card data are expected, pointing to insect abundance and conservation benefits resulting from increased plant diversity and ground cover associated with cover crop treatments. 

Participation Summary

Education & Outreach Activities and Participation Summary

1 Webinars / talks / presentations

Participation Summary

60 Farmers
20 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

An on-farm demonstration/field tour was planned for the summer of 2020 to highlight any impacts of the different treatment combinations on sweet corn growth and insect damage. However, due to COVID restrictions, a virtual field tour was performed instead and made available on youtube. As of January 2021, the video has been viewed 80+ times. Unfortunately, it is impossible to know the breakdown of famers vs. agricultural educators or service providers reached. Other forms of outreach have also been limited this year as a result of COVID, and I am hopeful there will be more opportunities to disseminate these research findings later in 2021. 

Project Outcomes

Project outcomes:

We anticipate the proposed research will contribute to agricultural sustainability by identifying non-chemical alternatives for insect pest control in sweet corn via natural enemy enhancement through modification of the typical crop environment. However, since processing of the abundance of samples collected during the growing season is still underway, actual outcomes are currently unknown and will be obtained over the upcoming months. 

Knowledge Gained:

As the project has yet to be completed, the overall picture of knowledge obtained from this study is incomplete. However, we anticipate gaining knowledge regarding the use of cover crops and living mulches in sweet corn production for insect natural enemy enhancement and overall insect biodiversity enhancement, as well as non-chemical methods of pest reduction.  Future directions of research are yet to be determined as the outcomes of the current study are still unknown. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.