Final report for GS17-176
Vegetable crops rely on frequent insecticide applications to control multiple insect pests in order to meet the high quality standards for commercial fresh market. Reducing insecticide use can save growers money, reduce human and environmental exposure, and help foster more sustainable vegetable production. Reducing insecticide use can be achieved by enhancing naturally occurring biological control of pests. One potential way to enhance this ecosystem service is by planting wildflower plots on farms. Wildflower plots provide extra resources and shelter to beneficial arthropods. The proposed research will measure the effects of wildflower plots on: the biological control of important pests, plant damage, and yield of collards and tomatoes. Biological control will be assessed using sentinel egg masses and sampling arthropod communities. Measurements will be taken on 20 farms located on the Delmarva Peninsula and around Virginia Beach. The expected outcome of this project is to provide growers strategies on how to increase naturally occurring biological control to be more sustainable and environmentally friendly without compromising yield or crop quality. Information will primarily be disseminated to growers through extension events and publications. Findings will also be presented at scientific meetings and in peer reviewed, scientific publications.
I. Measure the impacts of wildflower plantings on the abundance and diversity of arthropod natural enemy communities;
II. Determine if wild flower plantings enhance biological control of pests and crop yield;
III. Disseminate information to growers and researchers.
Data was collected at 22 farms during the summer of 2017 and 2018. Of these farms, 10 had wildflower plots established on them in the spring of 2016. The other 12 fields served as control fields. At each field, we grew collards from May to June, and tomatoes from June to August. These two crops reflect the cropping patterns of small scale vegetable farms in the study area. To measure pest control services, crops were scouted each week for pests, sentinel egg masses were used to quantify biological control, yield and pest damage were quantified.
Crops were scouted on a weekly basis for pests. Pest identity and abundance was recorded for each plant. On collards, Pieris rapae L. and Plutella xylostella (L.) were the primary pests found. On tomatoes, Spodoptera ornithogalli (Guenée) and Manduca spp. were the two most abundant pests. Two species of Manduca were observed, M. sexta (L.) and M. quinquemaculata (Haworth). Due to the similar biology of these two species, they were analyzed together.
Sentinel egg masses
Sentinel egg masses were used to measure biological control. Trichoplusia ni (Hübner) eggs were used on collards. Halyomorpha halys (Stål) and Helicoverpa zea (Boddie) eggs were used on tomatoes. These three species represent significant pest species for their respective crops. Masses were glued to wax paper and fastened to the bottom sides of leaves. Masses were left in the field for 48 hrs. Four egg masses of each species were deployed at each field. Two rounds of egg mass deployments were done each year. The rate of biological control was measured as the proportion of eggs remaining after the exposure period.
Pest damage was recorded on all the harvested tomatoes and collards. Leaf defoliation was recorded on collards as the proportion of leaves damage by pests with chewing mouthparts. For tomatoes, stink bug and chewing damage caused by arthropods were recorded.
Collards were once-over harvested after five weeks of growth from their transplant date. Tomato fruits were harvested as soon as they reached the breaker stage. Tomatoes fruits were picked from mid-August to early September. Collards yield was quantified as being marketable or unmarketable following USDA guidelines. Tomato yield was quantified according to the USDA grading standards.
No differences were found for weekly pest abundance between wildflower and control field for P. rapae and P. xylostella on collards and S. ornithogalli on tomatoes. Wildflower fields had significantly fewer Manduca spp. larvae compared to control fields. Wildflower fields had one larva fewer than control fields. There were no differences between control and wildflower fields for egg predation for all species. No differences were found for yield and pest damage between wildflower and control fields.
The results from this study underscore the needs for regional tests of the effects of wildflower plantings. Different results may simply be due to the different crops, pests, natural enemies, and climate observed in each study. The number of pest species in blueberry fields in Michigan did not differ between control and wildflower locations; but, egg predation was enhanced at wildflower fields (Blaauw and Isaacs 2015). In a study conducted with tomatoes in Italy, wildflower fields had a more abundant and diverse natural enemy community that did not translate into yield gains (Balzan et al. 2016). Pest damage to tomatoes was greater at wildflower fields compared to control fields (Balzan et al. 2016). A study using wheat as the focal crop found that wildflower plots decreased pest abundance, pest damage, and increased yield (Tschumi et al. 2016).
Another explanation for the lack of improvements by the wildflower plots could be because the effect of the landscape surrounding the farms is overriding the potential effects of the wildflower plots. In an experiment that placed both control and wildflower areas on the same farm, wildflower fields failed to enhance biological control and yield of strawberries (Grab et al. 2018). However, it was found that the amount of natural cover in the surrounding landscape had a positive effect on biological control and yield (Grab et al. 2018). A similar effect may be occurring with the wildflower plots in this study, as the locations were selected to be along a gradient of the amount of natural habitat in a 1-km radius around the site.
Balzan, M. V., G. Bocci, and A.-C. Moonen. 2016. Utilisation of plant functional diversity in wildflower strips for the delivery of multiple agroecosystem services. Entomol Exp Appl. 158: 304–319.
Blaauw, B. R., and R. Isaacs. 2015. Wildflower plantings enhance the abundance of natural enemies and their services in adjacent blueberry fields. Biological Control. 91: 94–103.
Grab, H., K. Poveda, B. Danforth, and G. Loeb. 2018. Landscape context shifts the balance of costs and benefits from wildflower borders on multiple ecosystem services. Proc. R. Soc. B. 285: 20181102.
Tschumi, M., M. Albrecht, C. Bärtschi, J. Collatz, M. H. Entling, and K. Jacot. 2016. Perennial, species-rich wildflower strips enhance pest control and crop yield. Agriculture, Ecosystems & Environment. 220: 97–103.
Educational & Outreach Activities
Academic posters and presentations
Enhancing biological control in vegetable production in eastern Virginia and Maryland. C. McCullough and M. E. O’Rourke. Graduate Student Research Symposium, Blacksburg, VA. March 2018
Enhancing biological control in vegetable production in eastern Virginia and Maryland. C. McCullough and M. E. O’Rourke. Entomological Society of America Annual Meeting. Denver, CO. Nov. 2017 Poster.
Pollinator habitat for enhancing biological control and pollination services. G. Angelella, C. McCullough, M. E. O’Rourke Entomological Society of America Annual Meeting. Denver, CO. 2017
Field days and outreach
Blue Ridge Wildflower Society – Roanoke, VA 2019
Virginia State University Field Day – Painter, VA 2018
Quail Cove Farms Honeyfest – Machipongo, VA 2018
University of Maryland LESREC Field Day – Salisbury, MD 2018
Accomack Master Gardener Meeting – Painter, VA 2017
NRCS Cover Crops Field Day – Painter, VA 2017
From the research gathered here, growers can plant wildflower plots to try and enhance ecosystem services knowing that they are not likely to make pest problems worse. Biological control of pests may be enhanced, but that was not seen in this study.
Farm-scale additions of wildflower plots may not be enough to increase biological control of insect pests in these production systems. With wildflower plots in particular, plot quality may also play an important role in determining their effectiveness. Empowering people engaged in agriculture to make farm-scale changes may help some; however, larger scale schemes may need to be created to increase the effectiveness of the biological control.