Organic Broadcaster

Research shows wild pollinators’ impact on strawberry production

By Nathan Hecht, University of Minnesota

Nathan Hecht, a graduate student at the University of Minnesota, won the juried poster session in the Organic Research Forum at the 2018 MOSES Conference. This article explains his research, titled “Recruiting Wild Pollinators in a Strawberry Agroecosystem.”

The story of this research project arcs back to the first time I attended a MOSES Conference in 2012 as a recent biology graduate of Luther College. I was working as a farm intern at Canoe Creek Produce in Decorah, Iowa, and was inspired to attend while dreaming about the bounty of a diversified organic market-garden operation. At the conference, I was inspired by a presentation given by Eric Lee-Mäder from the Xerces Society about farming for biodiversity, integrating resources and habitat for beneficial insects into the farming landscape. This vision of agroecology, of an agricultural landscape that was agronomically and ecologically productive, fascinated me. What if we could steward win-win models where the goals of both food production and conservation were possible?

I spent the next three years as a Peace Corps Volunteer in the high Andes of Peru, and among other experiences, was deeply struck by the rapidly melting glaciers, the reality of impending water scarcity, and the need for biodiverse landscapes that could support more resilient and adaptable farming livelihoods in the face of a changing climate and an uncertain future. I had a forceful realization that, as a global community, we could no longer divorce ourselves from the health of the land—if we are to thrive, we need to commit to a sustainable, resilient, regenerative, productive use of the land we depend on. My drive to learn more about agroecology brought me to the University of Minnesota (UMN) for a master’s degree in Applied Plant Sciences and to further investigate the potential of farming for biodiversity.

Experiment
For the past 9 years, the UMN Fruit Research team has been developing an organic strawberry production system that extends the Midwest strawberry harvest from a few weeks in June to the entire growing season. The pillars of this new system are day-neutral strawberries, a variety that flowers and fruits continuously throughout the growing season, and a plasticulture, low-tunnel production system. The low-tunnel design helps to resolve many of the greatest challenges to growing organic fruit in the Midwest: weeds, disease, water management, and a short-growing season.

Despite its many benefits, this organic system has been slow to catch on, in part, perhaps, due to the discomfort of many organic growers with input-intensive production. Given my background and interests, I became curious whether a more agroecological approach might have promise.

I was able to locate my experiment on organically certified land at the West Central Research and Outreach Center (WCROC) in Morris, Minn., in collaboration with Steve Poppe, a former strawberry grower and WCROC’s lead horticultural scientist. We designed the experiment to include less external inputs by seeding winter rye between rows instead of using landscape fabric, and choosing not to install plastic low-tunnels (Fig. 1).

Fig.1: The pollinator farmscaping strawberry production system (right) includes a strip of borage to attract pollinators. The photo on the left shows the University’s plasticulture, low-tunnel organic strawberry system.

The next step was to consider how we might add functional biodiversity to this annual production system, specifically, by planting an attractive floral resource to recruit wild pollinators and the pollination services they might provide the strawberry crop. This practice of pollinator “farmscaping,” where a grower provides additional habitat and floral resources to support wild insect pollinator populations, is finding renewed interest from many growers and researchers alike.

This is especially so given emerging threats to the honeybee industry, including colony collapse disorder. With the knowledge that 75% of global food crops depend on animal pollination at least to some degree, the importance of wild insect pollination services in agroecosystems has been a focus of recent research. While pollinator farmscaping practices are finding renewed interest in grower and scientific communities, many questions remain about how these practices can be beneficial to crop production and the agroecosystem.

Strawberries (Fragaria x ananassa), though able to self-pollinate, have been shown to produce higher quality fruit when flowers are more thoroughly fertilized by pollinating insects. A handful of studies have identified the benefit to on-farm pollinator populations when additional floral resources are provided near strawberry fields.

My study uses borage (Borago officinalis), a blue star-shaped flowering herb, as a floral resource for pollinators (Fig. 1). It is highly attractive to bees, competes well with weeds, flowers continually, is edible, and is considered a companion plant for strawberries in some gardening books, although I’ve found no published research about this pairing.

While a recent study showed increased pollinator abundance in strawberry rows adjacent to annual wildflower strips, there is as yet no literature examining the yield benefits of single-species flower strips in strawberry production, despite evidence that bees may benefit more from flower plantings of single species rather than heterogeneous mixtures.

My research investigates the potential of an annual borage flower strip to recruit wild insect pollinators and thereby facilitate pollination services in an organic day-neutral strawberry production system.

Research Results
I gathered data on strawberry fruit production and insect presence, and examined how these variables changed with distance from the flower patch. My hypothesis was that strawberry flowers closer to the borage flower patch would receive more insect visits, be more fully pollinated, and produce bigger, higher quality strawberries.

With increasing distance from the experimental flower strip, average strawberry yield and pollinator abundance appear to decrease (Fig. 2 & 3), with a significantly lower average berry weight in the plot farthest from the flower strip, compared to the first 50 feet.

Primary strawberry flower visitors were hoverflies (Syrphidae) and native sweat bees (Halictidae), suggesting strawberry pollination may rely more on fly (Diptera) species than bee (Hymenoptera) species. The borage patch itself hosted a wide diversity of insect pollinators including those mentioned above, as well as an impressive abundance of bumble and honey bees.

 

Looking Ahead
Although these results are only from the first year of data, it appears there may be a berry weight benefit for those strawberry plants located closer to the borage flower patch, due to increased insect pollinator activity. Many questions remain about how best to design pollinator farmscaping elements on a farm in order to reduce issues like space limitations, pollination competition, or pest hosting. Still, there is mounting evidence to suggest that adding floral diversity to a pollination-dependent cropping system may benefit both the farmer and local beneficial insect populations.

There are many ways to incorporate these sorts of pollinator farmscaping practices into your own plot, whether that is in a home garden or a large-scale production operation. This can begin with simply mowing less, to allow early season flowers like clover and dandelions to thrive when floral resources are low. Planting annual flowering species can be one way to experiment with flower plantings at low cost, with little risk. Some flower strips could even serve as secondary crops, as many flowers are edible, have medicinal properties, or can be sold as cut-flowers. More long-term permanent establishments include perennial flower plantings or even restored prairie landscapes. The Xerces Society (xerces.org) has many resources available to help design and integrate these sorts of practices on farms.

Concluding Thoughts
As we work to manifest the vision of diverse, productive, resilient agroecosystems, collaboration and knowledge-sharing will become increasingly important. The education and networking efforts of organizations like MOSES are critical, in that they connect more people to the conversation on supporting biodiversity in agriculture, myself included. As a graduate student, I am continually inspired by the many collaborations I see happening between growers and scientists, each bringing their own expertise to find new and creative solutions to complex challenges. I am hopeful that these partnerships will continue, with growers reaching out to extension professionals and professors to share their experience, and scientists reaching out to growers to develop research projects that are more directly associated with the needs and interests of local farming communities. Although there are countless challenges, I am encouraged by visionary growers, researchers, and leaders who have the power to create a world where both ecology and economy can thrive.

Nathan Hecht is a graduate student in the Organic and Sustainable Horticulture Lab at the University of Minnesota. His research is funded in part by the Minnesota Agricultural Experiment Station. To discuss his research, contact him at hecht072@umn.edu.

From the May |June 2018 Issue

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