A comparison of weed, pathogen and insect pests between low tunnel and open-field grown strawberries in New York

Highlights

• Tunnels provided an optimal environment for growing day-neutral strawberries, regardless of UV selectivity.

• Some pests, namely Tetranychus urticae, reached significantly higher densities under tunnels compared to the open-field.

• Lygus lineolaris densities were high in low tunnel and open plots, resulting in high proportions of unmarketable fruit.

• Infestation by Drosophila suzukii and pathogens on foliage and fruit were low under tunnels compared to the open field.

• Overall weed abundance was similar between open and low tunnel plots, but higher under low tunnels on several dates.

Abstract

While growing strawberries under plastic low tunnels is an increasing trend in the northeastern U.S., the effect of low tunnels on the incidence and severity of arthropod pests, pathogens, and weeds is largely unknown and presents a possible barrier to commercial adoption. During 2018 and 2019, we identified and quantified pest abundance on low tunnel versus open field grown strawberries at a research site in Geneva, New York, and compared these trends under three plastic types in 2019. Overall, we found that while yield and fruit marketability increased under tunnels of all plastic types compared to the open-field, ground-dwelling and foliar herbivores (mostly Tetranychus urticae) abundance was higher under low tunnels compared to open plots. In contrast, herbivores caught on clear sticky cards were more prevalent in open plots than under tunnels. A neutral effect of tunnels was present for Lygus lineolaris density and weed biomass during both years, although damage by L. lineolaris decreased under UV-limiting plastics. Tunnels also reduced infestation by Drosophila suzukii and several pathogens on foliage and fruit. This study provides needed information on pest communities of low tunnel strawberry in the Northeast, and could be used as an essential foundation for future IPM research.

Introduction

A major limitation of commercial strawberry (Fragaria × ananassa Duchesne) production in the northeastern United States is the short and unpredictable growing season (Orde and Sideman, 2019). Growers can address this issue by growing day-neutral cultivars (i.e., those that will fruit continuously under optimal temperatures) under polyethylene plastics, specifically low or high tunnels (Castilho et al., 2015; Lopez et al., 2017; Neri et al., 2012). This production system offers growers in temperate continental climates a way to sustainably produce high-quality strawberries for six months of the year, and protects plants against rain, wind and frost damage (Anderson et al., 2019; Lewers et al., 2017; Orde et al., 2018; Petran et al., 2017; Sorkel et al., 2006). However, while growing under plastic tunnels often results in higher yield, tunnels may also support higher pest pressure compared to the open field, leading to low adoption by growers in the Northeast (Wallheimer, 2017; personal communication with K. Reeves, a local grower in western New York). Determining how plastic tunnels, and specifically low tunnels, impact pest communities is necessary to promote this profitable and sustainable system.

Low and high tunnels provide a warmer, drier and protected environment that can lead to improved overall plant growth (Anderson et al., 2019; Orde and Sideman, 2019; Voća et al., 2007). Those same changes in the abiotic environment can also enable pest proliferation. Indeed, past studies on several high tunnel crops including raspberry, tomato, broccoli and cucumber found higher arthropod pest abundance under high tunnels compared to open fields (Ingwell et al., 2017; Leach and Isaacs, 2018). In addition, higher temperatures under low tunnels can result in earlier and more aggressive weed growth. Weeds interfere with harvesting, provide secondary hosts for invertebrate pests and pathogens, and directly compete with strawberry plants (Braun and Sutton, 1987; Pritts and Kelly, 2001). Although weeds under high tunnels are known to be a major issue, few studies have evaluated weed pressure under low tunnels (Goldy, 2012).

In above examples, plastic tunnels provided a suitable environment for pests leading to higher densities. Other studies, however, indicate the opposite trend and suggest that plastic tunnels provide an inhospitable environment for pests, leading to reduced abundance. Plastics may prevent insect pests from locating their hosts by physically blocking them (as was observed for spotted wing drosophila (Drosophila suzukii Matsumura) (Leach et al., 2016; Rogers et al., 2016)), or by disrupting their navigation process by limiting UV transmission. For example, lower infestations of Japanese beetle, whitefly, aphid and thrips have been observed under UV-blocking plastics compared to those transmitting UV (Antignus, 2000; Antignus et al., 2001; Cramer et al., 2019; Doukas and Payne, 2007). In addition, observations of strawberry pathogens including powdery mildew (Podosphaera macularis Wallr.), common leaf spot (Mycosphaerella fragariae Lindau), leaf blight (Phomopsis obscurans Sutton) on leaves and Botrytis cinerea Pers. on fruit indicate that plastic tunnels also reduce incidence of these diseases (Kumar et al., 2011; Lewers et al., 2017; Orde et al., 2018). Keeping plants dry and blocking UV transmission by photoselective plastics are possible mechanisms reducing infestation of these diseases under low tunnels (Tan and Epton, 1973).

Although past studies have evaluated the effects of tunnel environments on individual pest species, the comprehensive effect of covered production on broader pest communities, including generalist insects and mites, pathogens, and weeds is unclear (Al-Khatib, 1995; Cross et al., 2001; Husaini and Neri, 2016; Wallace and Webb, 2012). In New York, where low tunnels could benefit crop production and contribute to IPM, such basal information is necessary prior to widespread implementation. Thus our first objective was to characterize the low tunnel strawberry abiotic environment during the growing season by recording daily temperatures and relative humidity. Our second objective was to survey common pathogens, weeds and invertebrate pests found on low tunnel versus open-field grown strawberry during two seasons. Lastly, our third objective was to determine how UV-selective plastics affect pest abundance.