7/2/2013 - By Matthew Shultz

Shot hole… we have all seen this bacterial disease on plants, whether we know it or not. Shot hole affects all stone fruit trees and shrubs, which include fruiting and flowering plums, cherries and peach plants. The disease is often confused with insect feeding, because as the pathogen progresses, small little holes show up on the leaves closest to the ground and work their way up through the canopy of the plant. The small holes resemble a shot gun blast, hence the name shot hole.

The bacterium Xanthomonas arboricola pv. Pruni is the pathogen that causes these symptoms. The pathogen overwinters on fallen leaf litter or in lesions of the host plant. The first symptoms show up as water soaked spots in early spring, then become necrotic, and eventually fall out. Copper sprays right at bud break will help to kill the overwintering stage, and pay large dividends through the growing months.

Since I have gotten many calls regarding this disease in the last week or two, the best control this time of year is to lightly trim back any infected material. Then spray the crop with Phyton 27 (20oz/100 gals). I worked with Cease during my days as a grower, and it showed some promise with keeping shot hole off of Prunus cistena, as long as the plants were cleaned up with a few copper sprays first.

I would recommend reapplying Cease 2-3 times in a row at 14 day intervals, and then rotating in a copper. Do not mix copper products with any other chemistries. Fore , Dithane, and Junction can also be used in rotation. As mentioned above, shot hole is a bacterial disease and it needs water to reproduce, so susceptible crops will benefit from being taken off overhead irrigation.

By Matt Shultz, Horticultural Tech Support Specialist and Sales Representative, Harrell’s LLC and Marshall Horsman, Technical Services Manager, Harrell’s LLC.