In Santa Clara county, and in most of California, our past winter season was unusually wet. Who knows for sure what this coming winter will be like, but there is a forecast for El Niño,
which is likely to mean another wet year. While that sounds better than a drought, the disease pressure on our peach trees is likely to be quite high! Last year I just did not get to
any dormant spraying, and the peach leaf curl was a big problem. This year I aim to improve that situation!

In order to be effective at controlling the fungus which causes peach leaf curl, spraying must be done before symptoms are present. Once you see the new curled leaves, it is too late!
Some long time orchardists use the “holiday spraying” plan; Thanksgiving, Christmas, and Valentines, with that first spraying time being the most important, and the last only being
necessary if rains persist. There may still be leaves on the tree at the end of November, but that does not matter for spraying.

Copper based sprays have long been recommended for control of fungal diseases on fruit trees, but effective sprays are perhaps somewhat difficult for the home grower. Fixed copper
sprays, such as Kop R Spray Concentrate (Lilly Miller) and Liqui-Cop (Monterey Lawn and Garden) can be purchased for home use. Another fungicide under the brand name
“Daconil” can also be used by the home grower. Be sure to follow all instructions on the package!
After several years of using copper spray, there can be a build up of copper in the soil, which can inhibit soil microbial activity.

What is a home grower who prefers an “organic approach” to do….?

I have not yet tried the following, but I do plan to! Joe Real is a scientifically minded member and long time home grower of many types of fruiting plants. He has shared with us his
recipe for management of peach leaf curl.

Italian Dressing Recipe for Peach Leaf Curl by Joe Real

1. Add 2 oz of 5% vinegar to 1 gallon of water. Always add acid to water and not the other way around. (5% vinegar is regular household white distilled vinegar)
2. In a small cup, mix well together 2 TBSP of Melaleuca Oil, 1 TBSP of Neem Oil, 2 TBSP of Dawn Liquid dishwashing soap. (Melaleuca oil is also known as tea tree oil, and the active ingredient in Neem Oil is Azadirachtin)
3. Add to the 1 gallon diluted vinegar solution, and stir well, hence oil and vinegar and it makes for Italian Dressing.
4. Mix and Shake very well like you would an Italian dressing before spraying.
5. Spray during bud swell, but not during the full bloom, and when air temperature is above 40 deg F but below 75 deg F, preferably in the late afternoon. (This advice for seasonal timing seems contrary to spray suggestions from the UC system)

Joe writes that any commonly available Tea Tree and Neem Oil products will work well. He also indicates that a diluted version of the same spray can be used during the growing
season for control of mildew and other fungal diseases, by mixing the same ingredients with 2 to 3 gallons of water instead of 1 gallon.

A stronger version of the spray is also possible if disease pressure has been very high, and Joe mentions using this in his vineyard. The difference is using hydrogen peroxide as a
spray, followed by the “Italian Dressing” recipe. Normal drugstore 3% hydrogen peroxide is mixed with 5 parts of water prior to spraying (i.e. 1 cup HP, and 5 cups water). While the HP
spray is still wet, the vinegar based spray is applied. This is more effective in low light conditions.

As far as I know, this spray program has not been trialed in comparison to copper or Daconil (Chlorothalonil) and should be considered an experiment.

Please note that the UC IPM pesticide link indicates that bees may be sensitive to the active ingredient in Neem Oil, so spraying when bees are not attracted to the area should be
considered.