Last week I posted about our peach tree.  It was clearly sick but I could not be certain what was wrong with it.  The top 4 disease candidates each required a vastly different treatment, so I asked for help from blog readers in diagnosing the trouble more definitively.

Thanks for the posts with suggestions, info, and links!  Several comments suggested peach leaf curl, which is the most common disease to affect peach trees and thus statistically the most likely to be what’s afflicting our leafy little pal.  And from the pictures we took, it does look like this could be the problem.  But what did not reflect very well in the pictures was the clear pattern of holes in the leaves, and the lack of any thickening and puckering.  So the first disease I eliminated as a viable candidate was peach leaf curl.

Among diseases/infestations that could cause holes in the leaves were one caused by a bacteria, one by a fungus, and one by a beetle.  The following c0mment, however, from Rich Johansen of Josensen Ranch in Nevada County, provided a description that helped pin our trouble down exactly:

“This looks like a fungus caused peach blight, coryneum blight or usually called shothole fungus. Infected buds, shoots, and leaves may die. The spots on the
maturing peaches and nectarines turn scablike, drop off, and leave rough,  corky lesions. Prune out the infected branches immediately, prune beyond the infection. Disinfect the pruners after each cut.

Spray lime sulfur in the fall immediately after leaf fall. Now if the spots are brown or black it could be bacterial leaf spot. The surface of the fruit may be dotted with brown to black spots, and become pitted and cracked. Sunken lesions may form on the twigs. No adequate control for this disease-spray copper sulfate ( not OMRI approved) in the spring at bud opening will help suppress it.

Spring rainfall helps spread the bacteria. There are resistant varieties.  Hope this helps. “

I really appreciate all the feedback on this problem.  We agreed with Rich that our problem was shothole fungus.  We thought only one tree, our peach, was affected, but in thinking carefully about the description of the coryneum blight aka shothole fungus,  and looking carefully at our tree and its neighbors, I realized that the fungus probably originated months ago in the neighboring nectarine, which had the rough, corky lesions on its young fruit as described.  We’d been unable to diagnose this, had removed the fruit, and the nectarine showed no other ill effects in the ensuing weeks—until on closer examination this past weekend, while up treating the peach tree, we saw the beginnings of the telltale red spots on a handful of its leaves.

We followed Rich’s advice yesterday and pruned both trees to remove the affected parts.  The nectarine required slight pruning but the peach has only a half dozen remaining leaves after pruning.  It’s unlikely it will survive, but we want to see what effort is required to treat this disease and whether those efforts are warranted in first-year trees.  This is our first, experimental orchard and therefore we are using it to learn and to help us in future decisionmaking.

We’ve prepared a separate video for this blog, documenting our experience with this disease and how to prune off diseased parts.

Dan