FIMBY: It's late November, and your peach tree needs spraying

This is another post in our Food in My Back Yard series, devoted to edible gardening.

A sad scene in the spring is someone bringing a small branch or cluster of new peach leaves to the UC master gardeners at the Fair Oaks Horticulture Center or another garden event. The leaves are curled and puckered, with some distortions resembling red bubbles.

"What's wrong with my peach tree?" the person asks. And, kindly, the master gardeners answer: "It's peach leaf curl. You can spray for it, but not now, not until winter."

That time is now, peach fans. The rain is gone for the time being. If the tule fog stops haunting us for awhile, those of us with peach or nectarine trees can finally start treating them for peach leaf curl.

Peach leaf curl, caused by the fungus Taphrina deformans, is a disease that distorts and blisters the tree's leaves, and can defoliate an infected tree. Any fruit that develops in that situation is subject to sunburn.

And the disease can come back annually, once established. Left untreated, the tree can decline and have to be removed.

The recommended control is spraying a copper-based fungicide all over the tree once the leaves have fallen and been completely removed from that location. (Discard any leaves that show signs of disease -- don't compost them.)

The copper sprays available for home gardens nowdays have less copper in them than ones sold before 2010, to be environmentally friendlier. But they still can help control the fungus. Gardeners used to be advised to use Thanksgiving, New Year's Day and Valentine's Day as memory aids. In rainy winter climates like ours the advice now is at least one good spraying during dormancy in late fall/early winter, with a second spray in late winter, before bud swell.

The trick is that the weather does not often cooperate. Rainy or foggy weather thwarts plans because the spray needs calm, dry conditions 24 hours beforehand and afterwards to be effective.

But even one spraying session, if that's all that can be managed, can help. I've seen some recommendations that the first, late-fall spray is the key one. But orchard expert Ed Laivo, in speaking to the Sacramento County master gardeners recently, emphasized that the success of the last spray is the most important.

A February treatment, before the buds start to show pink, has been all I could manage in some rainy years, and my little tree had only a few leaves showing signs of curl. 

Any infected leaves will drop in spring and eventually be replaced by new ones that are OK if the weather stays dry. The pathogen also can infect green twigs and shoots, and even occasionally infects the young fruit.

Some peach and nectarine trees are more susceptible to leaf curl; check the variety's resistance if you're shopping for a new tree. 

The saddest case of peach leaf curl I've ever seen was on the O'Henry espaliered tree at the Horticulture Center. In 2023, continued rains prevented adequate spraying, and the tree developed such a bad case of the fungus that it looked as if it had been burned. The O'Henry is a popular heirloom variety; the delicious peaches probably are worth the trouble. (The tree looked fine and was productive the next year, thanks to UC experts' diligence.).

The University of California Integrated Pest Management system has excellent information online about peach leaf curl, fungicides and related tree care.

Here's what IPM says on the fungicides:

-- The least toxic yet effective fungicides available for backyard trees are copper soap (copper octanoate) or copper ammonium, a fixed copper fungicide. 

-- Add 1% horticultural oil to either of these copper sprays to increase effectiveness. Horticultural oil alone is not effective for peach leaf curl.

-- Copper may build up in the soil from repeated use, posing a risk to waterways. You can alternate copper use with the fungicide chlorothalonil.

The fixed-copper products available now to home gardeners are Kop R Spray Concentrate (Lilly Miller brands) and Liqui-Cop (Monterey Lawn and Garden). Both are copper ammonium complex products.

The IPM application recommendations are:

-- Thorough coverage with any fungicide is essential to obtain adequate disease control. Trees should be sprayed to the point of runoff or until they are dripping.

-- When using pesticides, always read and follow the label for usage, rates, toxicity, and proper disposal. Proper protective clothing and gear including goggles should be used when handling any pesticides.