Recent hail injury, especially when combined with excessive rains, is of concern for disease control in peach orchards as we move forward through the remainder of the season. Frequent summer rains generally increase the risk of green fruit rot. If inoculum is present during the green fruit stage and if long wetness periods occur (30 hours plus), additional infections are likely to develop throughout the season. To reiterate, when present, green fruit rot dramatically increases the risk of heavy pre- and post-harvest brown rot pressure. I would shift from sulfur-based programs to captan on hail damaged orchards – assuming that sufficient non-damaged fruit will be available for harvest. Removal of hail damaged fruit may not be economically feasible, but removal of this fruit from the orchard would be desirable. Again, it is recommended that the FRAC 3, 7, and 11 fungicides be reserved for late-season pre-harvest sprays. However, utilization of these may be judiciously warranted if hail damage is severe. Adjust cover sprays or initiate pre-harvest brown rot sprays early when disease pressure is high.
Hail injury also greatly increases the susceptibility of fruit to bacterial spot infection, especially if the disease is present in the orchard prior to hail. As soon as possible after hail injury, make an application of Mycoshield (or generics of oxytetracycline) in sufficient water to provide for thorough coverage of fruit and foliage. Low rates of copper might also have an impact on disease, and some anecdotal information would support copper use for bacterial canker diseases that can result on injured stem/scaffold/trunk tissues. A tank mix of Mycoshield (or generics of oxytetracycline) with low copper rates could not hurt, and it might help.
Leucostoma and other fungal cankers are also likely to be worse on hail-injured trees. Though research-based information is not specifically available for fungicides and canker management following hail damage, Topsin M may have some activity against canker diseases that come in on injured tissue.
Please contact your local county agent should you have questions on this topic or any other disease issues in your peach orchards.