November 6, 2020 - By Bob Labozetta (UC Master Gardener, Mariposa) - One of the most beautiful trees in the home orchard is the peach tree. The long silky leaves and blushing fruit stand out among all the other crops in our gardens and orchards.

Unfortunately, in the Sierra foothills, there lurks a fungus Taphrina deformans… peach leaf curl, the most common disease found in backyard orchards. Also known as curly leaf, curly blight, and leaf blister, this disease affects the blossoms, fruit, shoots, and leaves of peaches and nectarines.

Cool (48℉ - 68℉), wet weather when leaves are first opening can trigger the symptoms of peach leaf curl. First, in the spring, reddish areas develop on the leaves that thicken and pucker and cause the familiar leaf curling and distortion. These infected areas turn yellowish and later grayish white as velvety spores flourish on leaf surface. Affected leaves eventually turn yellow or brown with some remaining on the trees and others falling off. At this point, affected leaves are followed by a second set of leaves that grow more or less normally unless wet weather continues. The energy a tree puts into leaf loss and production of the second set of leaves saps the tree’s vigor and leads to decreased tree growth and fruit production.

One way to avoid peach leaf curl is to choose resistant varieties. Select resistant peach and nectarine varieties such as Frost, Indian Free, Muir, Redhaven, Kreibich, and Q-1-8.

Once you have a tree with peach leaf curl, you will want to treat it. Physical or cultural controls include thinning fruit to at least 3 inches apart, removing diseased or cracked fruit and placing them in the trash (not your compost pile), fertilizing with nitrogen by mid-June with a well-balanced fruit tree fertilizer, adequately watering in dry weather, and cleaning up dropped leaves and fruit under the tree.

However, these may not be fully effective by themselves. Spray copper fungicides with lower Metallic Copper Equivalent (MCE) of around 8%. The most effective and safest of these contain copper soap (copper octanoate) or copper ammonium (a fixed copper fungicide). Effectiveness is improved by applying with 1% horticultural oil.

Follow the instructions for all chemical products and make sure you use appropriate safety equipment during application. Apply fungicide to the point of dripping three times during the dormant season: after leaf drop (around Thanksgiving), winter (around January1) and before bud swell (around February, depending on where you live).

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For assistance, contact our Helpline at (209) 966-7078 or at mgmariposa@ucdavis.edu. We are currently unable to take samples or meet with you in person but welcome pictures.

The U.C. Master Gardener Helpline is staffed; Thursdays from 2:00 p.m. - 5:00 p.m. 

Serving Mariposa County, including Greeley Hill, Coulterville and Lake Don Pedro
Please contact the helpline, or leave a message by phone at: (209) 966-7078
By email (send photos and questions for researched answers) to: mgmariposa@ucdavis.edu 

For further gardening information and event announcements, please visit: UCMG website: http://cemariposa.ucanr.edu/Master_Gardener
Follow us on Facebook at: https://www.facebook.com/mariposamastergardeners 

Master Gardener Office Location:
UC Cooperative Extension Office,
5009 Fairgrounds Road
Mariposa, CA 95338 

Phone: (209) 966-2417
Email: mgmariposa@ucdavis.edu
Website: http://cemariposa.ucanr.edu/Master_Gardener

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