I have had a lot of questions/concerns regarding bee health and bloom fungicides sprays. Even though bloom is nearing its end, I thought I would try and answer a few questions I have received – and finally had some time to research and formulate an answer to these questions.
Do fungicides applied during bloom affect bee health?
The short answer is “We don’t know.” Research has shown that fungicides that are applied around or at bloom do adhere to the pollen, and are brought back to the hive during the process of pollination. The fungicides then inhibit the growth of different fungi within the bee hive, decreasing the the microbial diversity of the bee’s food source. As of the Almond Board of California 2009 Research Proceedings, it is unknown whether or not the fungi affected benefit or harm the overall health of the hive.
Which Fungicides are transported back to the hive?
Researchers at the Carl Hayden Bee Research Center in Tuscon AZ found five commonly used fungicides in the bee bread (food source) of hives placed in almond orchards. These fungicides include Chlorothalonil, Cyprodinil, Fenbuconazole, Iprodione, Boscalid, and Pyraclostrobin. The amounts of fungicide appear to vary by orchard and timing of application – BUT – this data was only based on hives placed in three orchards with two or three samplings- for now. Also, it is not known which fungicides target which fungi, if they negatively affect bee health directly, and if they have a negative impact on the entire hive by reducing the quality of the food source. The research group headed by Dr. DeGrandi-Hoffman will be looking into these questions through this year.
What about Pristine (Pyraclostrobin-Boscalid) applications?
Essentially, we don’t know exactly how this fungicide affects fungal growth in the hive. In vitro studies from Dr. DeGrandi-Hoffman’s lab indicates that the low rates of Pyraclostrobin-Boscalid that are comparable to the concentrations applied in the field resulted in the reduced growth of all 12 fungi the group isolated from the bee bread. It varied from slight to complete growth inhibition. Future research will hopefully determine if the concentrations found in the hive are able to decrease fungal growth and if the reduction of fungal growth negatively affects bee health.
How should we adjust our spraying to prevent harm to our hives?
Again, I am unsure. My best guess would be to talk with your beekeeper regarding a fungicide spray program, make fungicide applications when the bees are not active, apply the fungicides only by ensuring the spray tank is clean, and apply when pollen shedding is low (usually in the evening). For the most part, fungicides are required, especially this year, to maintain a profitable harvest – but so are bees. I hope future research will help guide our fungicide application practices to reduce unwanted damage to bees during pollination.
Information sourced from G. DeGrandi-Hoffman. 2009. “Determining the effects of fungicide contamination on nectar and pollen on honey bee colony health.” Almond Board of California Research Proceedings. Technical Report.