Cover Crops to Attract and Sustain Beneficial Insects of High Tunnel Pests

The Problem: High tunnel vegetable production across northern New England has increased aided in part through the ‘High Tunnel Incentive’ from the USDA-NRCS, Environmental Quality Incentives Program (EQIP). This is because Northeastern farmers recognize extending their growing season enables them to generate greater revenues and adapt their crop production to the changing environmental condition. Over the past decade, growers have turned to high tunnels to mitigate the unpredictable fluctuations in temperature and precipitation and protect crops from extreme, unseasonable weather events to produce a greater diversity of high-value crops(1,2).

Organic food production is on the rise nationwide as consumers demand fresh produce that is ‘sustainably’ grown with fewer synthetic pesticide residues(3). In 2021, $11.2 billion dollars in certified organic commodities were sold in the US, which was up 13% from the $9.9 billion sold in 2019 whereby 54% was for crops ($6.1 billion)(4).  The number of certified organic farms has also risen 5% from 2019 to 2021. Vermont is a top state ranking 8^th for certified acres and was the only New England state represented in the top 10, nationwide(4). In Vermont, over 90% of the farms are small diversified, family-owned operations and specialty crops are critical for their economic survival(6,7). Vermont reported an increase in certified organic farms of 6% percent to 693 from 2019-2021 where 547 of those produce crops, primarily vegetables. For vegetables grown under protection, tomatoes are a top commodity and were valued at over $1.8 million and for other vegetables, over $1.3 million(4,5)

High tunnels prolong environments that are ideal for crop production but also provide favorable conditions for arthropod pests(8,9). In several surveys of high tunnel growers across the region(10-13) over the past decade, the top pests causing damage to tunnel crops were aphids, thrips, whiteflies, spider mites, hornworms and cucumber beetles. Aphids, thrips and spider mites are particularly problematic due to their small size and ability to hide deep within the crevices and within plant blossoms. These pests can go unnoticed by growers until extensive damage and population build up has occurred. Organic growers have limited options for managing these key pests in high tunnels. Conventional growers have an array of chemical insecticides. Organic producers often do nothing, accepting the loss, increase labor costs by washing off infested produce and picking out saleable crops, rely on biocontrols that require costly repeat applications or use a variety of reduced risk pesticides that are often broad spectrum(14). Not only does this affect the pests but also beneficial insects (natural enemies and vital pollinators) which may be visiting crops(15).

Adoption of Integrated Pest Management (IPM) is key to continue the downward trend of pesticide use, especially to protect beneficial insects while ensuring good yields of high-quality crops (15-17). The Northeastern IPM Center recently identified top priorities facing farmers. The top two extremely important activities in the region were pest id and management (67%) followed by pest management in high tunnels (58%)(18). Stakeholder needs have also been identified in several surveys of Northeast high tunnel vegetable growers that were conducted over the past decade by the PI and regional collaborators(10-13). Growers use a wide variety of IPM tactics in high tunnels, like scouting, crop rotation, natural enemies and habitat plants. There was an over 10% increase in habitat plant use to sustain beneficia insects from 2014–2019. When growers were asked what resources or information would help them manage insect pests in high tunnels, they were most interested in identification tools, regional biocontrol guidelines specifically for high tunnels and action thresholds for specific pests. When growers were asked what limits their greater use of biological control, 52% said a lack of knowledge about how or when to use them; 26% said biocontrol was too expensive, and 22% lacked confidence that biologicals work(13).

The solution: Diversified vegetable farming is a profitable and sustainable method of food production. However, it is challenging with management decisions focused on reducing yield risk by enhancing on-farm ecological processes(19). The use of biological control agents to manage pests is a viable management strategy when pest populations are detected in a timely manner and numbers are below a level that will cause economic damage (9,20-23). Because high tunnels are an ‘open yet closed’ environment that is in between a closed greenhouse environment and open field production, growers must implement two biological control strategies: conservation and augmentative. Conservation biological control uses human intervention to enhance the performance of wild/naturally occurring natural enemies for pest management whereas augmentative biological control uses natural enemies that are mass-reared in rearing facilities and released in anticipation of pest outbreaks(24). Use of flowering plants like cover crops to provide habitat for wild natural enemies is one of several strategies used for conservation biological control in agroecosystems(25,26).

The goal of this project is to investigate the use of flowering cover crops between high tunnels to attract beneficials to the crop production area. The top conservation practices implemented by Vermont agricultural producers are reducing or eliminating pesticide applications and providing wildlife and pollinator habitat (27). This project will specifically address the needs of growers of high tunnel vegetables related to the sustainable management of key arthropod pests and align with their priorities to protect beneficials on their farms. There continues to be a need for the development and refinement of existing IPM strategies, like the incorporation of cover crops that function as habitat planting to sustain beneficials, to combat pests in high tunnels. Research on the performance of IPM strategies for conservation of biocontrol in high tunnel settings is limited in northern New England, warranting more in-depth investigations into their implementation to increase grower adoption. Using cover crops adjacent to high tunnels to enhance beneficial insects would increase on-farm sustainability. This aligns with Northeast SARE’s outcome statement and improve the quality of life for farmers, their families and the community. It will lower environmental and health risks by reducing the need for pesticide applications while promoting soil and beneficial insect conservation.