Managing Agricultural Drainage Ditches for Conservation Biological Control on the Delmarva Peninsula

Progress report for LNE20-408R

Project Type: Research Only
Funds awarded in 2020: $197,728.00
Projected End Date: 11/30/2023
Grant Recipients: University of Maryland, College Park; University of Maryland, Eastern Shore; University of Delaware
Region: Northeast
State: Maryland
Project Leader:
William Lamp
University of Maryland, College Park
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Project Information

Summary:

1) Problem, Novel Approach and Justification.

Agricultural drainage ditches serve a necessary function for water management on all farms. Especially for the flat Delmarva Peninsula (coastal plain portions of Delaware, Maryland, and Virginia) and portions of New Jersey, ditches are necessary to drain the high water table during the year. In addition, ditch habitats may also provide valuable ecosystem services to producers by enhancing natural enemies of pests and increasing their biocontrol. More broadly, ditches serve as examples of how uncultivated land in and around fields can provide ecological benefits. The goal of this proposal is to determine how to manage ditches to enhance populations of natural enemies, and to work with farmers to test management methods on farms.

2) Hypothesis and Research Plan.

The hypotheses are that ditches can be managed to increase numbers of natural enemies and to increase their biocontrol of pests in adjacent fields. The objectives are designed to complement each other and will be conducted over three years. During Year 1, we will focus on testing specific management practices to help determine which practices applied to drainage ditches will enhance natural enemies. Experiments will be conducted primarily on University farm ditches. During Years 2 and 3, we will test management practices as a way to enhance natural enemy populations and performance in ditches and adjacent crops. Experiments will be conducted on University and private farms. At the whole farm scale, the final objective will be conducted using two ditches on each of five farms, over three years of sampling, to determine if ditch management does indeed enhance natural enemies and suppress pest populations by biocontrol.

3) Outreach Plan.

Results from Objectives 1 and 2 will be delivered to farmers participating with Objective 3 as ditch modification practices are discussed and selected. Additionally, pamphlets detailing beneficial arthropods, pests controlled by them, and the habitats that favor beneficial arthropods will be produced and disseminated to farmers, extension personnel, and conservation groups. Project performance will be highlighted at other in-season events, such as research field days. Websites will be used to disseminate video clips, project summaries, and photographs of ditch management methods and natural enemies. Results will be shared at winter meetings, and project briefs will be prepared for trade journals.

4) Project Objective.

Our specific objectives include 1) to conduct experiments designed to enhance populations of natural enemies (e.g., spiders, predatory mites and beetles, and parasitoid wasps) in ditches by providing resources for shelter, food, and reproduction, 2) to compare natural enemy performance in ditch habitats and adjacent crop fields across a range of habitat conditions, and 3) to use ditches on farms to demonstrate the value of this enhancement of natural enemies for pest management.

Project Objective:

Our objectives are 1) to conduct experiments designed to enhance populations of natural enemies (e.g., spiders, predatory mites and beetles, and parasitoid wasps) in ditches by providing necessary resources for shelter, food, and reproduction, 2) to compare natural enemy performance in ditch habitats and adjacent crop fields across a range of habitat conditions, and 3) to use ditches on farms to demonstrate the value of this enhancement of natural enemies for pest management.

Introduction:

Agricultural fields are frequently disturbed, and natural enemies that serve as biological controls of pests must colonize the fields from elsewhere.  Drainage ditches, because they are frequently left undisturbed, may be a source of natural enemies.  Our long-term research is designed to determine what natural enemies are found in agricultural drainage ditches, and which ones move from ditches into fields during the production season.  Specifically for this project, our research aims to determine what ditch management practices will aid natural enemies to reproduce in ditches and to disperse from ditches into crop fields.  In this way, ditches may serve a valuable function of conservation biological control, whereby predators and parasites will suppress populations of arthropod pests.

An example of such a natural enemy from our research are jumping spiders, family Salticidae, in which certain species occur in drainage ditches in the spring.  As potential prey abundance decreases in the ditch during the summer, the spiders disperse into neighboring crop fields to locate new types of prey.  These predators follow a typical life history pattern of beneficial species: they reproduce in unmanaged areas and survive overwinter, then in late spring/summer they disperse into crop fields and locate injurious insect pests before reproducing in late summer and fall.  We seek to encourage natural enemies to use ditches located within crop fields, and thus become a source of dispersing biological control agents into the adjacent fields.

Although our research funding began in spring, 2020, the pandemic stopped any potential research until June.  As a consequence, this year we only performed preliminary research, and postponed most of our research to be conducted in 2021-2023.  The Lamp lab established a study on an agricultural drainage ditch at the University of Maryland Wye Research and Education Center as a randomized complete block design with four treatments and four blocks.  During summer and fall, we used pitfall traps, sweep samples, and sticky card traps to identify species of natural enemies and the pattern of their occurrence.  For example, from the pitfall traps, we identified lycosid and linyphiid spiders, carabid and staphylinid beetles, formicid ants, gryllid crickets, and several families of parasitoid wasps.  We have initiated treatments on the plots to determine how ditch management practices such as mowing or the addition of straw may help beneficial natural enemy species.

In another study, the Zebelo lab performed research to determine the movement of natural enemies from ditches to adjacent crops, and to measure predation rates of those natural enemies on insect pests.  Measurements were taken in plots in which vegetation was cleared using chemicals while adjacent plots were left uncleared.  Natural enemy abundance was higher adjacent to uncleared ditches, suggesting that they are a source of natural enemies such as parasitic wasps, spiny stink bugs, ladybird beetles, and pirate bugs.  Using caterpillars as prey, they measured predation rates on cabbage adjacent to the ditch plots.  They measured high predation rates, however no differences were found between cleared and uncleared plots.  The experiment will be repeated next year.

Studies planned by the Owens lab were cancelled because of the pandemic.  The start delay to June prevented the planting of various flowering plants, designed to attract natural enemies.  In addition, restrictions by the University of Delaware prevented the recruitment of wage labor.  The project will be discussed during the 2021 AgWeek Agronomy session and additional farms will be located for studies.  In addition, a survey is being prepared for use during the winter meetings to determine how agricultural drainage ditches are managed. 

Cooperators

Click linked name(s) to expand
  • Dr. Simon Zebelo (Educator and Researcher)
  • Dr. David Owens (Educator and Researcher)

Research

Materials and methods:

Our proposal has two hypotheses. First, we hypothesize that ditches can be managed to increase numbers of natural enemies by providing needed resources for shelter, food, and reproduction of beneficial species. Second, we hypothesize that ditches can be managed by planting flowering and non-flowering species to increase their biological suppression of pests in fields adjacent to ditches, thereby lowering pest populations and decreasing the need for insecticide applications.

To determine how ditches can be managed to enhance the number of natural enemies in ditches, an experiment was begun on an agricultural drainage ditch at the University of Maryland Wye Research and Education Center.  Sixteen plots were created, set up in four blocks of four plots, and each plot was assigned a treatment.  No treatment was applied during the summer, 2020, so the sampling of natural enemies was conducted to identify species and their abundance before any treatment was started.  One treatment was started in fall: the addition of straw to the sides of the ditch.  Other treatments will start in spring, 2021.  Sampling consists of pitfall traps, sweep samples, and sticky card samples.  We hypothesize that the addition of straw, and perhaps other management practices, will enhance the numbers of natural enemies compared to the control plots.

Participation Summary
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.