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

Authors: PESSEREAU, ELIZA - University Of Wisconsin; Franco Jr, Jose; Duff, Alison; GRATTON, CLAUDIO - University Of Wisconsin

Submitted to: Agriculture, Ecosystems & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2025
Publication Date: 4/21/2025
Citation: Pessereau, E.J., Franco Jr, J.G., Duff, A., Gratton, C. 2025. Early spring-flowering winter cover crop (Camelina sativa) increases insect flower visits in Wisconsin (USA). Agriculture, Ecosystems & Environment. https://doi.org/10.1016/j.agee.2025.109689.
DOI: https://doi.org/10.1016/j.agee.2025.109689

Interpretive Summary: The Northern Corn Belt is dominated by intensified agricultural production that relies heavily on vast acreages of single species crops, resulting in wild pollinator population declines. Winter cover crops can provide a number of soil benefits while also introducing diverse crops onto the landscape. Winter camelina is one of the few winter cover crops that can reliably overwinter in the cold climate of the Upper Midwest and also bloom early in the spring at a time when few floral resources are available for pollinators. This research evaluated the value of including winter camelina as a winter cover crop when planted alone or in a mix with other overwintering cover crops for pollinators in a corn silage production system. We found that planting winter camelina alone or in mixtures both provided similar amounts of floral resources in the spring, which resulted in similar pollinator visitation, but provided more resources as compared to winter fallow (i.e., no winter cover crops). Dandelion, a common weed in cultivated fields, was also present in abundance and provided floral resources but pollinators preferred to visit winter camelina, suggesting planting this winter cover crop can result in positive biodiversity benefits. We also found that fall planting had an impact on floral availability in the spring, with a mid-September planting date providing earlier and overall more flowers in the spring, resulting in greater overall resources for pollinators. With the inclusion of flowering overwintering cover crops like winter camelina, row crop and dairy forage producers can diversify their crop rotations and reap positive biodiversity benefits on their farms by supporting populations of wild pollinators.

Technical 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.