It seems an unlikely time to be spraying fruit trees — late fall, as the trees go dormant. For Peach Leaf Curl it is the ideal time to prevent its occurrence next spring. It is especially important to take preventive measures if your trees were infected this past growing season. This is one disease for which there is no cure once it becomes established for the season. Premature bud swell following a mid-winter thaw in mild climate areas may make tissue susceptible to the disease. Timely prevention is the only control.
Peach Leaf Curl fungus overwinters between buds scales. Symptoms appear about 2 weeks after leaves begin to emerge. Fungal growth starts when temperatures approach 48̊F, with 68̊F optimum for disease development. Cool wet weather for more than 12 hours favors disease development and slow leaf growth with prolonged exposure — the perfect conditions for Peach Leaf Curl to become entrenched. In many spring seasons, green tissue and disease spores develop so quickly that the opportunity to prevent the disease from taking hold is lost before the backyard gardener is even aware of what has taken place. Once temperatures climb above 80̊F, the weather turns warm and dry and young tissue has stopped developing, disease spread ceases.
Leaves, shoots, blossoms, and in severe cases, fruit of peaches and nectarines can all be affected by Taphrina deformans, the Peach Leaf Curl fungus. Visual symptoms include puckered, thickened leaves that turn red or purplish and eventually yellow or grayish-brown when covered with spores, before falling from the tree. Diseased twigs will be thickened, stunted and often die. Severe infestations may cause corky, cracked areas on fruit later in the season. Repeated infections weaken the tree leading to reduced crops and eventual death.
A few leaf curl resistant varieties exist — Avalon Pride, Charlotte, Early Crawford, Frost, Indian Blood Cling Indian Free, Muir, Nanaimo, Oregon Curl Free, Peregrine and Q-1–8 peach and Kreibich nectarine. However, most of these varieties are not considered to be of highest quality. Additionally, most of these varieties are not particularly hardy and are best suited for the West coast. Many gardeners choose to grow other varieties and take disease prevention steps in order to enjoy higher quality fruit and hardiness. Redhaven and many of the Redhaven derived varieties are said to be tolerant to the disease, though not truly immune, while offering high quality fruit and hardier trees.
Keeping trees as strong as possible if unexpected infection occurs will help trees recover for the next season. Irrigation and a sound soil fertility program is very helpful. Judicious application of extra nitrogen to encourage new growth can be beneficial. Thinning fruit more than normal will also help maintain tree vigor.
A very limited number of Peach Leaf Curl control materials are available to the home gardener. The synthetic fungicide chlorothalonil is one. It is currently the only non-copper fungicide available for managing Peach Leaf Curl on backyard trees. Bordeaux mix, lime sulfur and copper –based fungicides have also been used in the past. Several of these materials have recently been or are in the process of being withdrawn from the market. So, your best bet would be to check with your local extension service office for currently available choices.
For effective control, trees should be sprayed until they are dripping or to the point of run-off. Several days of dry weather must follow application for control to be effective. Addition of a spreader is helpful in insuring that the spray achieves full tissue coverage.
Plum Pockets — A closely related disease
Related fungi, Taphrina communis and T. pruni, can cause Plum Pockets disease on wild plums. Domestic (European) plums are occasionally affected while Japanese plums rarely suffer the disease. Preventive sprays for both diseases are the same. If you have had problems with Plum Pockets, consider protecting those trees as well when you apply your Peach Leaf Curl protection.