Peach problems are the pits; how to protect fruit trees from leaf curl
Q: When should I be dormant spraying my fruit trees? Earlier this year I asked about peach leaf curl on my peach tree and was told that prevention in the form of at least two dormant sprays was the best treatment, but I don’t remember when I was supposed to spray. Is it too early to start?
A: Peach leaf curl is a disease of peaches and nectarines that causes their leaves to curl and become distorted. In bad infestations it can cause defoliation, crop loss, damage to the fruit or loss of tree limbs.
Peach leaf curl is caused is by a fungus called Taphrina deformans. This fungus thrives between November and May, when daytime temperatures range between 48 and 87 degrees Fahrenheit and we have cool wet weather. Once temperatures warm up beyond 87 degrees Fahrenheit, or relative humidity drops and things dry out, new infection of leaves stops. Leaf buds and young leaf tissue, the most susceptible to symptoms, will also stop when leaves are no longer developing. Once you start to see the yellow, warty and curled leaves it’s too late to treat the disease for that year. As the disease progresses the cells in the leaf swell and pucker, and the twigs become distorted. With severe infections, fruit production is drastically reduced and the surface of the skin on the fruit may develop cracks and cork-like bumps.
Prevention is the best treatment. The fungus spores infect the trees through the bud scales. These are the protective sheath around each leaf bud. During cool, wet weather the spores multiply on the bud scales and bark, and then infect the shoots and leaves as they emerge in spring. Once the peach leaf curl fungus is on the peach leaf, it produces germ tubes that penetrate the young leaves causing the leaf distortions.
By treating trees with a good dormant spray during the winter and early spring the fungus is killed, preventing it from overwintering and infecting the new growth in the spring.
To treat your trees, spray until they are dripping with a copper-based dormant spray three times during the winter months. These treatments should be spread out during the dormant season.
- Plan to do the first spray now, around Thanksgiving, once the tree has dropped its leaves for the winter.
- Spray again about a month later, around New Year’s Day.
- Spray one last time right before Valentine’s Day.
Before the first spray, rake up and dispose of all old and newly dropped leaves. If the tree was severely infected this summer, prune the tree now to reduce the number of spores that will over winter. When spraying the tree also spray the trunk and area under the tree. After cleaning up around the tree, place a new layer of mulch under and around it to limit any fungal spores from splashing back onto the tree.
Avoid spraying if rain is forecast. Rain washes the dormant spray off the tree. Dormant sprays work best if they can sit on the tree several days before rain washes them off.
As always, please follow all label directions when using any type of fungicide or pesticide.
For a more in-depth discussion of peach leaf curl, please see the University of California Pest Notes for Home and Landscape at https://bit.ly/30NdFDQ.
The Shasta Master Gardeners Program can be reached by phone at 530-242-2219 or email email@example.com. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.