Early spring-flowering winter cover crop (Camelina sativa L. Crantz) increases insect flower visits in Wisconsin (USA)

Abstract

The expansion and intensification of agriculture in the last century has reduced floral resources for wild insect pollinators, contributing to their decline and potentially lowering pollination services for crop production. Flowering cover crops that can overwinter in harsh climates, such as winter camelina (Camelina sativa [L.] Crantz), can provide key resources for spring-emerging insects and fit into forage cropping systems in the Upper Midwest region of the United States where corn silage production is an important source of dairy forage. However, the amount of floral cover and length of time that cover is available, as well as the practicality of integrating camelina in annual forage cropping systems, depends on fall planting time and cover crop mix. We performed a plot-scale, randomized block experiment to measure spring floral cover and insect flower visitation of winter camelina and uncultivated flowers. This experiment occurred across 2 years in 3 cover crop mixes: 1) camelina monoculture, 2) camelina, triticale, hairy vetch mix, and 3) camelina, cereal rye, hairy vetch mix. In the second year, 3 camelina monocultures were planted at three different fall planting times, which constituted additional treatments: 4) early, 5) mid, and 6) late plantings. We included an unseeded fallow treatment, i.e., no cover crop, for comparison. Cover crop mixes and camelina in monoculture planted simultaneously (all mid-fall plantings) provided equal amounts of floral cover and supported comparable insect visitation rates the following spring. For monocultures, camelina planted earlier in the fall had the highest spring floral cover, and the latest planting time provided virtually no flower cover. Despite the large proportion of total floral cover attributed to dandelion in many plots, flower visitation exclusively increased with increasing camelina floral cover. However, there was an upper asymptote at which adding more camelina did not further increase visitation. Our study demonstrates that winter camelina can provide resources for insects in early spring when planted in a monoculture or mix the previous September as compared to winter fallow, though the period of flowering is short. We also show that although dandelion may provide floral cover early in the growing season, camelina may be more attractive to insects and provides an important spring floral resource.