Pollination of Red Clover in Minnesota1

Abstract

Observations on pollination of mammoth red clover (Trifolium pratense L.) in Roseau County of northern Minnesota indicated that honey bees (Apis mellifera L.) remained at a low level of abundance on red clover until sweetclover (Mellilotus alba Desr.) had gone out of bloom. Late-season honey bee activity on mammoth red clover was important in effecting late seed crops of 138 to 354 pounds of seed per acre. In Clearwater and Polk Counties of northwestern Minnesota, where medium red clover was the only legume grown for seed, honey bees were important pollinators of the medium red clover. Partial correlation calculated from observations on 18 fields of second-crop medium red clover indicated that honey bees were more important than bumble bees (Bombus spp.) in determining seed yields. Partial regressions of yields on average counts of honey bees and bumble bees indicated that bumble bees were more efficient than honey bees. Abundance of honey bees and seed yields decreased as the distance between red clover fields and apiaries increased. Pollination by honey bees accounted for yields of 193 to 456 pounds per acre when bees were located adjacent to the fields of medium red clover, while at distances of greater than 1 mile from the nearest apiary pollination by honey bees was insignificant.