Stella Otto: The Backyard Fruit Gardener

Today's Tip: Mow vegetation short around the base of fruit trees and bushes to reduce winter habitat for rodents.

Peach Leaf Curl — Control it Now!

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.

Dis­ease Symptoms

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.

Cul­tural Control

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.

Fungi­ci­dal Control

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.