Scientists at Cornell University “found a shocker” when they analyzed two dozen environmental factors that may be at play in the decline in bumblebee populations: “Fungicides,” says a Cornell release. “The scientists discovered what they call ‘landscape-scale’ connections between fungicide usage, pathogen prevalence and declines of endangered U.S. bumblebees.”
Until now, fungicides were regarded as benign as far as bees are concerned, since they are aimed at plant diseases. The bees, as pollinators, pick up fungicide residue while foraging. Assistant entomology professor Scott McArt said many fungicides “are known to interact synergistically with insecticides, greatly increasing their toxicity to the bees.” The Cornell release cited chlorothalonil as an example. The fungicide has been linked to stunted colony growth in bumblebees and increased vulnerability to infection by the fatal Nosema infection.
The Missouri Botanical Center says chlorothalonil in an organochlorine fungicide sold in different formulations and under trade names that include Daconil and Bravo. The chemical provides “broad spectrum control of vegetable, flower, fruit and ornamental diseases including but not limited to anthracnose, leaf blights, downy mildew, powdery mildew, leaf curl, scab, black spot fusarium leaf spot and many other diseases.” It is considered to show low toxicity to birds and bees.