Several gardeners have contacted me recently because their stone fruit trees have leaf curl damage.
Unfortunately for these gardeners they have already lost the battle this season in controlling the disease.
Curly leaf is a difficult one so I did a little research on the Internet and came up with the following from the University of California USA.
“Peach leaf curl, also known as leaf curl, is a disease caused by the fungus Taphrina deformans.
Peach leaf curl affects the blossoms, fruit, leaves, and shoots of peaches, ornamental flowering peaches, and nectarines, and is one of the most common disease problems for backyard gardeners growing these trees. The distorted, reddened foliage that it causes is easily seen in spring. When severe, the disease can reduce fruit production substantially.
Peach leaf curl first appears in spring as reddish areas on developing leaves. These areas become thickened and puckered, causing leaves to curl and severely distort. The thickened areas turn yellowish and then grayish white, as velvety spores are produced on the surface by the leaf curl fungus.
Later affected leaves turn yellow or brown and can remain on the tree or may fall off; they are replaced by a second set of leaves that develop more normally unless wet weather continues.
The loss of leaves and the production of a second set result in decreased tree growth and fruit production. Defoliation in spring may expose branches to sunburn injury.
The peach leaf curl pathogen also infects young, green twigs and shoots. Affected shoots become thickened, stunted, distorted, and often die. Only rarely do reddish, wrinkled to distorted (or hypertrophied) areas develop on fruit surfaces. Later in the season these infected areas of fruit become corky and tend to crack. If leaf curl infection builds up and is left uncontrolled for several years, the tree may decline and need to be removed.
Leaf symptoms appear about 2 weeks after leaves emerge from buds. The fungus grows between leaf cells and stimulates them to divide and grow larger than normal, causing swelling and distortion of the leaf. Red plant pigments accumulate in the distorted cells. Cells of the fungus break through the cuticle of distorted leaves and produce elongated, sac-like structures called asci that produce sexual spores called ascospores, which give the leaf a grayish white, powdery or velvet like appearance.
The ascospores are released into the air, carried to new tissues, and bud (divide) to form bud-conidia. The fungus survives the hot, dry summer as ascospores and bud-conidia (these are asexual spores) on the tree’s surfaces. When the weather turns cool and wet in fall, the ascospores germinate to produce more bud-conidia. The new and old bud-conidia continue to increase in number by budding. Eventually a film of bud-conidia is formed on the tree’s surface. In spring, the bud-conidia move by splashing water from irrigation or rain and can infect new leaves.
Periods of cool, wet weather, when leaves are first opening on the tree, favor the disease. The optimum temperature for fungal growth in laboratory cultures is 68°F, the minimum is 48°F, and the maximum is 79° to 87° F. Budding of bud-conidia occurs at or above 95% relative humidity. Wetness from rain, dew, or irrigation for over 12.5 hours at temperatures below 61°F is needed for infection. Maximum infection occurs when trees are wet for 2 or more days. Although leaves may be infected, symptoms may not appear if temperatures remain above 69°F. (20C) Cool weather prolongs the period of disease development by favoring the pathogen and slowing leaf growth. Development of peach leaf curl ceases when young tissue is no longer developing or when weather turns dry and warmer 79° to 87°F (26 to30C).
To prevent peach leaf curl, treat peach and nectarine trees with a fungicide every year after leaves have fallen. (Use Lime Sulphur or sprays of potassium permanganate) Generally a single early treatment when the tree is dormant is effective, however, in areas of high rainfall or during a particularly wet winter it may be advisable to apply a second spray late in the dormant season, preferably as flower buds begin to swell, but before green leaf tips are first visible.
Copper. The most commonly used treatment, the greater the amount of copper particles, the more effective the product will be. (Use copper hydroxide such as Liquid Copper rather than copper oxychloride) However, other factors like coverage, use of additives like stickers and spreaders, (Raingard) and frequency and duration of rain, which can wash off the copper, will also impact product effectiveness. In all cases, the copper is active only when it is wet, when the copper ions are in solution”.
This season I tried a different treatment for one of my stone fruit trees, instead of using the copper sprays.
I kept an eye on the developing leaves and when the first sign of any curly leaf appeared I then sprayed all the leaves within reach with Vaporgard, ensuring that both sides of the leaves were covered with the film. A couple of days later I gave the tree and surrounding soil a good spray of potassium permanganate (Condys Crystals). Since then I have done nothing but observed the results which is only about 20% of the leaves are affected by the disease. Most of the original leaves with the Vaporgard are good and its the ones that I had difficulty spraying that are most affected.
Another advantage with the Vaporgard is its UV shield aspect which protects the chlorophyll and allows the leaves to produce more energy from the sun. The result is a better crop.
What to do now if your tree has heaps of curly leaves and not too many good ones?
Well you could spray the good leaves with Vaporgard to improve their energy gaining potential.
The badly affected leaves will fall off to be replaced by new good leaves and these too could be sprayed with Vaporgard. This will assist in improving the size of the potential crop.
If the tree is too badly damaged then likely no crop this season. After leaf fall in the autumn spray the tree all over with Lime Sulphur. Leave for a while and in the middle of winter spray with potassium permanganate. In the new season at the first sign of the disease on the new foliage spray with Vaporgard and then start a program with Liquid Copper sprays mixed with Raingard on a frequency of every 7 to 10 days.