Fungicides Can Reduce Pollination Potential

Authors: Alarcon Jr, Ruben; DeGrandi-Hoffman, Gloria; WARDELL, GORDON

Submitted to: Western Farm Press
Publication Type: Other
Publication Acceptance Date: 3/7/2009
Publication Date: 3/7/2009
Citation: Alarcon Jr, R.N., Hoffman, G.D., Wardell, G. 2009. Fungicides Can Reduce Pollination Potential. Western Farm Press. Vol 31(7) pp. 17 & 21.

Interpretive Summary: Growers perform tasks to ensure a bountiful crop, including pest management which typically requires the application of formulated herbicides, insecticides, and fungicides. Fungicides are frequently considered safe for use around bees, yet during the 2008 almond bloom, we noticed that bees stopped foraging along the sprayed rows. In addition, dead bees were found outside of several colonies which suggested the sprays were toxic to the bees. Other studies have reported adult bee toxicity from fungicide applications and when fungicides are mixed with other compounds, the mixture can be several times more toxic to bees than either product alone. High levels of fungicides in stored pollen might also inhibit the growth of certain strains of fungus that are necessary to convert pollen into bee bread. Aside from potentially harming and deterring bees from visiting blossoms, fungicides can also reduce fruit or nut set even though pollination has occurred. In laboratory experiments, most almond pollen exposed to fungicides failed to germinate and fungicide application can damage the stigma preventing fertilization. We recommend that tank sprayer is clean and free of insecticide residue and that the application of fungicides occur at the end of bloom.

Technical Abstract: Growers perform tasks to ensure a bountiful crop, including pest management which typically required the application of formulated herbicides, insecticides, and fungicides. Fungicides are frequently considered safe for use around bees, yet during the 2008 almond bloom, we noticed that bees stopped foraging along the sprayed rows. In addition, dead bees were found outside of several colonies which suggested the sprays were toxic to the bees. Other studies have reported adult bee toxicity from fungicide applications and when fungicides are mixed with other compounds, the mixture can be several times more toxic to bees than either product alone. High levels of fungicides in stored pollen might also inhibit the growth of certain strains of fungus that are necessary to convert pollen into bee bread. Aside from potentially harming and deterring bees from visiting blossoms, fungicides can also reduce fruit or nut set even through pollination has occurred. In laboratory experiments, most almond pollen exposed to fungicides failed to germinate and fungicide application can damage the stigma preventing fertilization. We recommend that tank sprayer is clean and free of insecticide residue and that the application of fungicides occur at the end of bloom.