Xanthomonas pruni can infect leaf scars on twigs as leaves drop in the fall. Bacteria overwintering in the leaf scars will initiate infections again next year if spring weather conditions favor infection. Where bacterial leaf spot was a problem in 1996, growers should apply a copper spray at leaf fall to reduce overwintering populations of this bacterial pathogen. Copper sprays applied at leaf fall are also effective against peach leaf curl. Note, however, that other fungicides registered to control peach leaf curl will not control bacterial diseases.
Bacterial canker is caused by the bacterium Pseudomonas syringae.
Bacterial canker on sweet cherries can be prevented by copper sprays applied either at leaf fall in autumn or before bud break in the spring. However, a copper spray applied to cherries in early spring can have adverse effects on pollination and cherry fruit set in years when there is little rainfall prior to bloom. In such years, copper residues in trees can be high enough at blossom time to affect the viability of pollen. Cherry growers concerned about inadequate fruit set may wish to control bacterial canker of cherries by using a fall application of copper rather than the dormant application of copper in spring. Geneva As with our recollections of the year's weather, we're often surprised when we see our perceptions of pest events compared with hard data.