We had a very dry late winter, and so the trees leafed out looking very good, even for those of us who don’t want to do annual spraying to prevent fungal disorders. But after the rainy cool days of April, the consensus according to our group forum, is widespread damage of the leaves.

There is little we can do to prevent more damage now that the fungal spores have made their presence known. It feels good to pluck off damaged leaves, and to rake them up, but these practices may or may not have an impact on the present situation. On the other hand, we can make sure the trees have plenty of what they need to make new leaves and restore their balance. Nutrition, water, and probably remove all the fruit if the damage on the leaves caused near defoliation.

And, we can plan for next year

An interesting study documented in UCCE, compared different spray treatment approaches on the different branches of individual trees, as well as some branches left untreated as control. This trial was done with a variety of types of peaches since some are more resistant to the disease. The differences in the branches were quite apparent visually. In addition to spraying, some branches were covered with medium weight Agribon, a breathable row cover product. This was applied before expected rain and removed after each rain. The idea behind the row cover was to keep the branches more dry since the fungal spores need damp conditions to spread.

The results

“Compared to untreated branches, those treated with Liqui-Cop averaged about 70% control, copper soap 80% control, and Agribon by itself just under 60% control, but these treatments were not statistically different. Agribon generally kept the branches dry, although some moisture was evident after heavy rains. Two treatments provided nearly complete control: (1) Agribon plus Liqui-Cop, and (2) lime sulfur (late fall) followed by Microcop (late winter). Maxicrop (kelp) did not work at all and substantially increased the severity on some of the branches.” (Please note that lime sulfur is no longer available for home use.)

Anecdotally, a local farmer suggests spraying should happen at Thanksgiving and Christmas, then again in late January or February if we have a lot of rain. The most important time to spray is right after leaf fall. Sprays for managing PLC, which are considered organic, contain copper. Copper can build up in the soil and can impact soil microorganisms and can leach into waterways. Home growers can also use synthetic fungicides containing chlorothalonil. Or we can try planting varieties that are considered to be less susceptible to the disease.

There is little that can be done to control the disease once the symptoms are present according to UC IPM notes. That said, a tent of Agribon or plastic applied before a late rain might help prevent those wet conditions the fungus likes for repeated infection on the branches. Generally, the diseased leaves are shed, and are replaced by healthy growth – unless it rains and is cool. The idea of being able to cover the tree is a great argument for keeping your trees small enough to manage easily!!