The use of native perennial wildflowers and alfalfa trap crops to increase pollination and biological control in strawberries

The use of native perennial wildflowers and alfalfa trap crops to increase pollination and biological control in strawberries

Summary

The purpose of this project is to provide small fruit growers in the Northeast with a simple and effective management strategy for enhancing biodiversity and ecosystem services (biological control and pollination) using native perennials and alfalfa in companion plantings. We expected that planting wildflower-alfalfa strips would increase abundance and diversity of native bees resulting in greater pollination services and higher fruit yields. Similarly, we expected the wildflower-alfalfa strips to increase parasitism rates of the tarnished plant bug resulting in decreased fruit damage and higher yields. Additionally we measured the relative benefits of using wildflowers or alfalfa alone or together to determine the role of each in enhancing ecosystem services and to explore potential synergisms.

Objectives/Performance Targets

My objectives are to:

1.Quantify the influence of wildflower-alfalfa strips on pollinator community composition and pollination services in strawberry.

                  Preliminary analyses of combined 2013 and 2014 field data using structural equation modeling and generalized linear mixed effects models show that pollinator abundance is higher in simple, highly agricultural landscapes than in complex landscapes with high proportions of natural area (Figure 1). These results are incredibly surprising and opposite of what we had predicted. Although bee abundance was not significantly different between plots with wildflower strips and without in either landscape (Figure 2) we did see that in complex landscapes damage to strawberry fruit resulting from poor pollination was significantly lower on plots with a wildflower strip (Figure 3). As we finish identifying bees to species we will perform community composition analyses to determine whether the decrease in poor pollinator damage was associated with more diverse bee communities. Although the literature suggests that wildflower strips should be most effective in simple highly agricultural landscapes, the studies these predictions are based on were conducted in extremely simplified landscapes with less than 2% natural area in central California and Germany. Even in the most agriculturally simplified landscapes in New York we had a minimum of 10% natural area. Interestingly, for farms in landscapes with high proportions of natural area those natural areas were generally characterized as deciduous or coniferous forests which are known to be poor bee habitat.

2. Investigate P. digoneutis biological control of tarnished plant bug to determine

        Preliminary evidence based on fruit damage assessments suggested that tarnished plant bug damage is greater where pollination services are high and poor pollination damage is low and indeed our structural equation models did show a positive pathway between pollinator abundance and tarnished plant bug damage (Figure 4).  Follow up studies showed that tarnished plant bug nymphs do show a preference for well-pollinated strawberry fruits and in simple landscapes wildflower strips tend to increase the abundance and damage of tarnished plant bug nymphs in the strawberry plots (Figure 5). Interesting tarnished plant bug abundance was significantly lower on wildflower plots in complex landscapes suggesting that biological control by P. digoneutis may be reducing their numbers. Parasitism rates of plant bugs will be determined in the next few weeks.

3. Disentangle the relative benefits provided by either wildflowers or alfalfa through increased pollination and/or biological control on strawberry yield.

          Alfalfa and the wildflower planted in the strips appear to be equally good habitat for tarnished plant bug. There were no statistically significant differences in tarnished plant bug abundance between plot treatments (control, with alfalfa, with wildflowers, with wildflowers + alfalfa) however tarnished plant bug abundance and damage was always lowest on plots with alfalfa suggesting that it was successful as a trap crop. Tarnished plant bug abundance was highest on plots with wildflower strips only suggesting that they increase spillover of pests into the crop.

• Figure5
• Figure1
• Figure2
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• Figure3

Accomplishments/Milestones

To accomplish these objectives we have established 36 paired 15’x20’ plots of Jewel, a June bearing variety of strawberry on 15 farms in the finger lakes region of NY. Half of the plots had a strip (3X20’) of native perennial wildflowers (10 species, we were unable to successfully grow the late figwort and alum root) planted as plugs parallel to an end row in October 2012. These plots also had a strip (2×20’) of alfalfa planted between the wildflowers and the end row of strawberry. All other sides of the plots had grass seeded with control plots at each site receiving grass on all sides. At three of the 15 farms two additional strawberry plots were established with either wildflowers only, or alfalfa only to address objective 3.

The project is progressing as planned and bloom on the wildflower strips in becoming more a abundant as the wildflowers mature. All plots have been maintained with hand weeding throughout the summer, they were fertilized with fishmeal and renovated in the fall, and mulched with straw in December.

During our second field season we collected both pollinators and tarnished plant bug nymphs on several occasions at each plots in the spring and collected fruit from each plot for damage and yield assessments. We have almost finished identifying all bee species collected to species and preliminary data analysis was conducted in the fall and winter.

Impacts and Contributions/Outcomes

If successful this project has the potential to significantly reduce pesticide use and reliance on managed honey bees for northeastern strawberry farmers. The adoption of wildflower-alfalfa strips for ecosystem services presents not only an economic gain for farmers but can also assist in the conservation of out native beneficial insects. Our preliminary data show that the alfalfa –wildflower strips may already be having a positive impact on majority of farms where they have been deployed. I have been in regular contact with the owners and managers of the farms where my research plots are located in order to share information about the insects I collected on their farms and the early results of the project. Through these interactions I have raised awareness about the potential for biological control of tarnished plant bug and the negative impact pesticides can have on its natural enemies. I have also called attention to the diversity of insect pollination of strawberry flowers and the current decline on abundance and diversity of our native bee species. As a result of my research I have been invited to give several talks related to conservation of ecosystem services including a public talk with the Finger Lakes Land Trust, an extension talk a the Cornell Small Fruit Open House and the Empire State Fruit and Vegetable Growers Expo. In the coming months I will prepare a manuscript based on our findings for publication and present the results at the Entomological Society Annual meeting during a symposium I am co-organizing.

Collaborators: