Preventive Care: Controlling Now For Peach Leaf Curl

PHOTO: Hard to beat a fresh peach.

It’s almost Thanksgiving – the soil is cooling, the garden is slowing, the nights are longer as we move inexorably toward the solstice. The recent storm that swept through the North State bringing welcome moisture also relieved many of the deciduous trees in my home garden of the last of the season’s biomass. The stark but elegant – almost defiant – beauty of bare tree silhouettes in my garden include most of my home fruit trees.

This phenological moment in a deciduous tree’s seasonal cycle is referred to as leaf-drop, and it’s a good indicator that your tree has gone dormant. Lots of gardening resource guides and organizations that give recommendations on what to do in your garden at this time of year list: Spray peaches and nectarines with copper spray in mid- to late- November.

I’m a gardener who tends toward a sort of loving and benign neglect of my plants. And in general, I’m not a spraying kind of gardener on principles of environmental impact, cost and labor.

But the dormant spraying of fruit trees is a fairly common recommendation from gardening agencies of all kinds and I have always wondered what the copper-based spray recommendation was about. This year I decided to find out more. PHOTO: A copper fungicide available from a natural and organic on-line retailer.

To help me understand, I turned to two reliable sources: Joe Connell, the Farm Advisor and County Director for the UC Davis Cooperative Extension office in Butte County, and backyard-orchardist for close to two decades and, Carl Rosato, farmer and owner of Woodleaf Farm, a 30-year old, 26 acre organic farm in the foothills outside of Oroville where he cultivates more than 50 varieties of peaches (among many other fruits).

Joe Connell chatted with me at length about this ubiquitous recommendation for using copper sprays, providing me with some history and technical input as well. “Copper-based sprays are strongly recommended specifically for the control of the fungal disease known as peach leaf curl (Taphrina deformans), which relentlessly affects peach and nectarine trees.” There are several controls, from heavy hitting chemicals to OMRI approved organic controls. PHOTO: Joe Connell.

As home-gardeners, Joe suggested, “we need to consider the acceptance of some level of imperfection. A hole here, a black spot there, a moth-hole here, is not the end of the world.” Unless it’s the end of your tree and thus crop. “One of the big issues with this disease, is that it can cause significant defoliation of your trees in late spring, leaving them exposed to sunburn in our early summer heat and this in turn leaves our trees very vulnerable to flat-headed borers, which will kill the trees,” However, with a little attention Joe reminds us that growing and caring for peaches in our region is not difficult, is very rewarding and this minor problem is easily handled with preventative care. In Joe’s experience fixed copper sprays are the most effective product available to home-gardeners. PHOTO: Deformation caused by peach leaf curl.

Joe went on to share that “Peach leaf curl is a fungus whose spores live and overwinter on the tree’s branches, stems and buds. Copper has been used since the 1700s when French vineyard managers realized its effectiveness at controlling fungal attacks by creating an inhospitable environment for the fungi to exist.”

So-called “dormant spraying” after the leaves fall in the Autumn (about Thanksgiving in Northern California) allows for much more targeted application that will not negatively impact the health of the tree during its more stressful growing season, or negatively impact the health or viability of its crop.

According to the UC Davis Integrated Pest Management site:

“Historically, the most commonly used fungicides available to home gardeners have been the fixed copper products. For all copper-containing products, the active ingredient, copper, is listed as “metallic copper equivalent,” or MCE, on the label. Various product formulations differ widely in their metallic copper content. The higher the MCE, the greater the amount of copper and the more effective the product will be. However, other factors such as coverage, use of additives as such stickers and spreaders, and frequency and duration of rain, which can wash off the copper, also will impact product effectiveness. In all cases, the copper is active only when it is wet, when the copper ions are in solution.

Fixed copper products (meaning those whose copper ions are NOT water soluble) include tribasic or basic copper sulfate, cupric hydroxide, and copper oxychloride sulfate (C-O-C-S), but currently only liquid products containing copper ammonium complex products with 8% MCE (e.g., Kop R Spray Concentrate [Lilly Miller brands] and Liqui-Cop [Monterey Lawn and Garden]) are available to consumers. The most effective copper product, 90% tribasic copper sulfate with a 50% MCE (Microcop), is no longer available to retail outlets, because the manufacturer withdrew the product in 2010, although remaining supplies still can be sold.”

“The copper ammonium complex products can be made more effective by adding 1% horticultural spray oil to the application mix; the oil also aids in controlling some aphids, scale insects, and mites. Copper soap (copper octanoate) fungicides are also available, and preliminary research indicates they may provide some protection of trees.”

“Be aware that repeated annual use of copper products over many seasons can result in a buildup of copper in the soil, which eventually can become toxic to soil organisms, and if it moves into waterways, can harm some aquatic species.”

Bordeaux Mixture
Copper sulfate is not a fixed copper and, when used alone, is less effective than tribasic copper sulfate or other fixed copper products. However, if copper sulfate is mixed with hydrated lime to make a “Bordeaux mixture,” (a nod to the French origins of the solution) the copper sulfate and calcium in the lime react together to form a fixed copper product that is effective against peach leaf curl.”

In Joe’s garden, he planted to have fruit maturing in his home for as long a period a time as possible and his trees include a Maygold peach, a Royal Blenheim apricot, an heirloom Fay Elberta peach, a Asian pear, and a Fuyu persimmon. The Fay Elberta is a disease-resistant variety, while the Maygold is more disease prone. While Joe does not always have trouble with peach leaf curl, when he does, he uses a copper spray regime the following winter. The first spray now, near Thanksgiving after leaf drop, and after you’ve done your first round of dormant pruning, and the second spray in late January, before the tree buds break dormancy. In terms of which spray to use, he recommends going to your trusted local nursery and finding out what they recommend and then follow the directions and precautions.

At Woodleaf Farm, famous for its peaches, Carl Rosato shared with me that in his 30 years of growing peaches, he has been able to significantly reduce the occurrence of pest and disease outbreaks on the farm with vigilant attention to soil and plant health and fertility, and other best farm management practices. But even he has peach leaf curl sometimes. PHOTO: Carl Rosato, photo courtesy of Carl Rosato.

There are drawbacks to any kind of spaying that is intending to kill something. Both men confirmed that while trace amounts of copper are necessary in our soils, when used excessively over long periods of time, the copper residue from copper sprays can build up in our soils – eventually harming soil microbes and potentially impacting groundwater with any large run-off. While lime sulfur will break down in the environment, it’s very caustic to skin and will corrode through metal, as a result, in most places, lime sulfur is no longer available to the home gardener in retail garden stores, while copper sprays are widely available.

Following research out of Oregon in the early 1980s that lime sulfur is far more effective on controlling for peach leaf curl than the copper sprays or the chemical formulations, Carl began using a lime sulfur spray in his orchard and has had good results. He sprays after a thorough fall leaf clean up and fall pruning to remove all dead, damaged or diseased material from his trees. He does a second spray close to Valentine’s Day. As a licensed chemical spray applicator, Carl is able to get lime sulfur at commercial vendors in 2.5 gallon increments and indicated that you can mix your own, but it’s not as effective as the commercial brands in his experience.

The take home messages from both sources were this: With a really relatively small amount of attention, growing fruit in your home garden is fun and NOT that difficult. If you’re going to grow peaches and nectarines, your first line of defense against peach leaf curl is choosing disease resistant varieties, such as the Fay Elberta peach and/or the Independence nectarine. Your second line of defense is dormant spraying at leaf-drop and again before bud-swell in spring with a copper or lime sulfur solution. PHOTO: A heavy summer fruit crop.

If you spray, no matter what you spray with, use common sense, spray only what you need and follow the directions on use, on storage and on disposal TO THE LETTER. These include things like spray when there are as few pollinating insects out as possible – for instance when it’s cold and/or early in the day. Do not spray when there is a breeze or when rain is predicted in the next 48 hours.

Be cautious and careful for your sake, the sake of your plants and foods and the sake of the soil and other living systems in your garden.

Joe Connell recommends the following pages for further good reading on home orchard care:

the backyard orchard at UC Davis: fruitsandnuts.ucdavis.edu

and the UC integrated pest management website: www.ipm.ucdavis.edu

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In a North State Garden is a weekly Northstate Public Radio and web-based program celebrating the art, craft and science of home gardening in Northern California and made possible in part by the Gateway Science Museum – Exploring the Natural History of the North State and on the campus of CSU, Chico. In a North State Garden is conceived, written, photographed and hosted by Jennifer Jewell – all rights reserved jewellgarden.com. In a North State Garden airs on Northstate Public Radio Saturday mornings at 7:34 AM Pacific time and Sunday morning at 8:34 AM Pacific time.

Jennifer Jewell
In a North State Garden is a bi-weekly North State Public Radio and web-based program celebrating the art, craft and science of home gardening in Northern California and made possible in part by the Gateway Science Museum - Exploring the Natural History of the North State and on the campus of CSU, Chico. In a North State Garden is conceived, written, photographed and hosted by Jennifer Jewell - all rights reserved jewellgarden.com. In a North State Garden airs on Northstate Public Radio Saturday morning at 7:34 AM Pacific time and Sunday morning at 8:34 AM Pacific time, two times a month.
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1 Response

  1. Avatar c says:

    Have pear trees where a whole branch will die early in the year, leaves turn brown and do not fall off. It happens on several varieties, and usually multiple branches on the same tree.

    Is there something that can be sprayed on pear trees to prevent this?