Blossom Protect: A New Biopesticide for Fire Blight Control

Recently the Pest Management Regulatory Agency (PMRA) announced the registration of a new product for apple and pear growers to help them battle fire blight in their orchards. Blossom Protect, a biological pesticide, is registered for control of fire blight, unlike other biological control products which are registered for fire blight suppression. Although there is not much experience with this product in Canada, it does appear to have some merit for pome fruit producers, especially when used in rotation with streptomycin for resistance management.

Blossom Protect consists of 2 containers, one with 2 live strains of the yeasts Aureobasidium pullulans, and another with a citric acid buffer, which are mixed together prior to application. The citric acid buffer lowers the pH in the blossoms which inhibits the growth and multiplication of the fire blight bacteria when they enter the blossoms. The lower pH also allows the yeast strains to colonize the same areas of the blossoms, blocking the infection site and utilize the same nutrients as the fire blight bacteria.

Blossom Protect can be applied up to 4 times per season at 10%, 40%, 70% and 90% open blossoms. Since the yeast strains need to get into and colonize open blossoms before the fire blight bacteria are introduced, it is recommended that this product be used during early bloom for best results. Studies have shown that applying Blossom Protect early can result in good fire blight control. One study showed that even when Blossom Protect was applied at 40% and again at 80% bloom, good suppression of fire blight was obtained. However, the authors admitted that an earlier application could have resulted in even better fire blight reduction. Fire blight predictive models, like Cougar Blight and MaryBlyt that predict fire blight infection risk periods, should be used to help growers target the best time to spray biological based products such as Blossom Protect.

There are a few precaution growers should be aware of when using this product. Some sensitive apple and pear varieties have occasionally shown enhanced russetting on fruit after Blossom Protect was used. Apple varieties such as Elstar, Golden Delicious, Idared, Jonagold, Sansa, Santana, Braeburn and the pear variety Conference appear to be sensitive to enhanced russetting, whereas the apple varieties Boskoop, Gala, Gloster, Goldrush, Pinova, Shampion, Kanzi, Topaz and the pear varieties Abate and Fetel did not show any russetting in studies. The manufacturer is suggesting that only 2 applications of Blossom Protect be applied in a given season to sensitive varieties. Studies have also shown that high rates of Blossom Protect can cause enhanced russetting particularly on the sensitive varieties and that late applications will also result in enhance russetting particularly with the onset of fruit set, so this product should not be used to control fire blight in rat tail blossoms.

Blossom Protect should not be tank-mixed with certain apple scab fungicides including Supra Captan 80 WDG, Maestro 80 DF, Equal, Syllit, or any fungicide that contains a strobilurin fungicide (group 11) such as Sovran, Flint, Pristine, since these types of fungicides are toxic to the yeasts. They can be applied 2 days before or after an application of Blossom Protect. Some apple scab fungicides (group 9) such as Scala SC and Vangard 75 WG are not toxic but are not recommended as a tank mix with Blossom Protect. Although it is not recommended to tank mix Blossom Protect with Streptomycin it can be used in rotation with streptomycin which will reduce the risk of resistance developing.

Blossom Protect can be stored for up to 10 months at room temperature (20oC) and up to 24 months in cool storage (8oC) or in a fridge. This will allow growers the flexibility of keeping unused product around for the next season which is not possible with some of the other biopesticides.

Blossom Protect is certified for use in organic apple and pear production by Washington State Department of Agriculture Organic Food Program in the United States Ecocert, the Research Institute of Organic Agriculture (FiBL) and InfoXgen in several European countries. The status of Blossom Protect for use in organic apple and pear orchards in Canada is not known at this time. Organic growers in Canada should contact their certification body before applying any products to confirm they are permitted for use.

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