- Vegetables: cucurbits
- Crop Production: cover crops, intercropping
- Education and Training: demonstration, display, extension, on-farm/ranch research
- Natural Resources/Environment: habitat enhancement
- Pest Management: biological control, integrated pest management, row covers (for pests)
Cucumbers (Cucumis sativus) are one of the most widely grown crops of the North Central Region, yet they are also one of the most likely to face pollination and biological control deficits. Natural enemies and pollinators require additional nutritional and habitat resources that are not found in conventional agricultural fields. The addition of flowering cover crops within the field could provide these resources. As of now, information on this topic, especially in cucumbers, remains limited. We hypothesized that pollinator and natural enemy abundance would increase in plots containing flower strips and that the effect would be greatest in the rows closest to the flower strips. Five flower strip treatments were used: 1) cucumbers (control), 2) buckwheat (Fagopyrum esculentum), 3) yellow mustard, (Brassica hirta), or 4) sweet alyssum (Lobularia maritima). Flowers were planted within a commercial cucumber field in a randomized complete block design with six replications in the 2014 growing season. Some floral treatments successfully attracted more beneficial insects than others, but the beneficials did not disperse out to the cucumber plants. Cucumber yield was unaffected. Habitat management for beneficial insects still holds a great deal of potential to improve yield, profitability, and sustainability, but questions as to its application in cucurbit agroecosystems remain.
In 2013, in Michigan alone, cucurbit crops (pumpkin, squash and cucumber) were grown on over 45,400 acres and valued at over $43.2 million (USDA/NASS, 2014). The region accounts for 37% of all U.S. acreage for these crops. In cucurbit crops, including cucumber, the insects causing the greatest economic costs in the NC Region are cucumber beetles, squash bugs, thrips, spider mites and seed corn maggot. Current insect management practices in cucurbit crops are highly dependent on a relatively narrow range of insecticides, which inadequately control several key pests and are cause for environmental concern. A large-scale conventional commercial cucumber grower’s standard insect pest management program in Michigan consists of about 8 broad-spectrum insecticide applications in any given growing season. Expenditures for insect management in these crops can easily exceed $100 per acre for pesticide applications alone (Barnett 2012). Despite these enormous pesticide applications, yield losses due to insects remain high. Alternative management strategies, such as the use of habitat modification with mulches and insectary plants can contribute to pest reduction by enhancing the activity of natural enemies. Winter rye windbreaks are commonly used in cucumber production systems to protect vulnerable seedlings and soils from damaging winds, but they are not particularly attractive to beneficial insects.
One of the many ecosystem services insects provide to growers is biological control. Enhancing the efficacy of natural enemies in controlling pests continues to remain an active field of investigation (Landis et al. 2000, Kleijn and Sutherland 2003, Bianchi et al. 2006, van Lenteren 2011, Walton and Isaacs 2011). Despite their desirability, declines in natural enemy populations in agricultural areas have been consistently observed, especially in highly disturbed areas (Sotherton 1998, Biesmeijer et al. 2006). Many studies have explored conditions that maximize ecosystem services, such as the addition of perennial flowering plants and fallow fields adjacent to cultivation, which increase the abundance of natural enemies (Long et. al 1998, Rebek et al. 2005, Wanner et al. 2006, Fiedler et al. 2008). Flowering species are rarely found adjacent to or within agricultural fields due to intensive herbicide use and the perception of revenue loss in from uncultivated space, but there is increasing support for the use of habitat diversification as a means to increase both the number and efficacy of beneficial insects. (Goverde et al. 2002, Carvell et al. 2006, Blaauw et al 2012). The effect of flowering windbreaks on natural enemies in cucumber production is not well-studied, warranting further investigation.
With respect to pollinators, growers in our region typically rent hives at a cost of $20-40/acre. In recent years, growers have observed reductions in fruit set and yield of their cucumber crops, and suspect that inadequate pollination may be contributing to substantial revenue losses. In response to decreasing honeybee populations worldwide, attracting and maximizing the efficacy of native pollinators has become of increasing interest (Isaacs and Kirk 2010, Petersen et al. 2013). In cucumbers, pollination is essential for proper fruit set, with inadequate pollination being associated with fruit abortion and low fruit quality (Stanghellini et al. 1997). The main pollinators of cucumber are honey bees (Apis mellifera) and the common bumblebee (Bombus impatiens), though the role of other pollinators is not well-understood (Smith et al. 2012). Wild pollinators, such as the common bumblebee, have been shown to pollinate cucumber more effectively than honey bees, even when managed honey bee hives are added to the field (Gajc-Wolska et al. 2011). Therefore, attracting wild pollinators to cucumber fields should be a priority. When grown adjacent to wooded or natural areas, the abundance of wild pollinators in cucumber fields has been shown to increase (Lowenstein et al. 2012, Smith et al. 2013). This may be due to the fact that native pollinators are often sensitive to environmental disturbances and require additional food and habit resources (Tuell et al. 2008, Williams et al. 2010, Winfree et al. 2011). Adding flowering areas within the field itself may provide these resources, thus increasing pollination. Native pollinators have been shown to be attracted to both annual and perennial flowering species in Michigan (Fiedler and Landis 2007a,b). Taken together, the literature suggests that adding flowering areas to cropped areas may enhance pollination in cucumber.
I predicted that the inclusion of flowering windbreaks in cucumber fields would: 1) increase the abundance of natural enemies 2) decrease the abundance of herbivorous insects, and 3)increase pollinator abundance and diversity , and 4) increase cucumber yield and quality. Additionally, we expect the effect of the flowering windbreaks to be the strongest in rows of cucumbers adjacent to the flowers, meaning that the will be greater abundance and diversity of beneficial insects and fewer pests in rows of cucumbers closest to the flowering annuals. Quinn_SARE_LiteratureCited
The immediate goal of this project was to evaluate the effect of the inclusion of flowering plant species in commercial cucumber (Cucumis sativus) fields on beneficial insect community composition to inform us of which flowering species enhance beneficial insect activity most effectively. Through presentations and other outreach, growers were educated on the value and effective implementation of flowering windbreaks in their own farms. The action outcome was to increase grower acceptance of this strategy, which in turn will lead to an overall increase in beneficial insect activity on their farms, thus increasing cucumber yield and profitability in the North Central Region.