Hail can injure the fruit and the bark of peach trees. It is opening wounds that pathogens can use to enter the plant tissue. Should a grower protect those open wounds until the healing process fends off pathogens on its own? Although sprays have often been recommended (and used) after hail injury, there seems to be little to no data as to how effective such sprays really are.
A poll among specialists in 2009 indicated that the incidence of bacterial spot (Xanthomonas) and gummosis (Botryosphaeria) can increase after a hail storm. But then, any fungi that colonize wood are aided by any injury. Bacterial canker (Pseudomonas syringae) infections are probably not a concern at time of fruit ripening. It is a more cool weather disease than a hot summer disease like bacterial spot.
So should you apply a fungicide after a hail storm? I think so. There is just too much at stake to take a chance. The long-term health of your trees is at stake. So here are my thoughts: The absolutely best way to deal with that issue is to apply a fungicide PRIOR to hail. That would eliminate spores and mycelium that CAN cause problems at the time. That of course is not a realistic approach as we do not know for sure in advance where and when hail is going to hit. The next best thing is to apply a fungicide as soon as possible after hail. Captan and Pristine have activity in reducing fungal gummosis, but they both do not have after-infection activity. Thus I recommend to apply Topsin-M or a similar product which has after- infection activity against the Gummosis fungus, at the high rate in combination with either Sulfur, Captan or Pristine (Sulfur, if there is no fruit to protect; Pristine, if you are close to harvest and inking is a concern; Captan, in all other cases). If the orchard has no history of gummosis, there is no need to spray anything because where there is no fungus, there is no infection. As mentioned before, hail during cool weather (spring time) may increase bacterial canker in areas that already have bacterial canker problems. In those cases, I recommend to add Mycoshield or a similar product. It can be tank mixed with Topsin-M.
Last updated 04/09