Curling leaves on Plants

Symptoms

On an affected tree, new leaves and shoots redden and pucker. The affected leaves become puckered and thicker than normal. The deformed areas are red to yellow at first and then turn brown. Brown areas come after the red to yellow stage.

Some leaves may yellow, or they may be covered with powdery gray spores. These signs are caused by infection with the fungus Taphrina deformans.

Shoots are affected as well as leaves. Affected shoots become thickened, stunted, distorted, and often die. Look at the new shoots as well as the leaves, because both redden and pucker.

Fruit can show symptoms too, although this is uncommon. The fruit surface becomes corky and cracked. Because the disease affects leaves, shoots, and sometimes fruit, check all three parts of the tree. Peach leaf curl typically affects only peach and nectarine trees, so check which tree you have. Taken together, the signs to look for are reddened, puckered new growth, thick deformed leaves that turn brown, and distorted shoots.

Causes

Infection by the fungus Taphrina deformans causes peach leaf curl. The fungus overwinters on twigs and buds. It survives the dry summer as spores. The hot, dry summer does not clear the fungus, because it survives as spores.

Periods of cool, wet weather, when leaves are first opening on the tree, favor the disease. Wetness from rain, dew, or irrigation is needed for infection. That wetness must last more than 12.5 hours at temperatures below 61 °F (16 °C). Irrigation counts as a source of wetness here, in the same way as rain and dew.

The threshold applies to the length of the wet period and to the temperature together. Wetness and cool temperatures are both part of the infection requirement. The disease typically affects only peach and nectarine trees, and those are the trees where this fungus causes it. Four conditions are named: the fungus, its survival on the tree, cool wet weather, and a long wet period.

Diagnosis

No look-alike problems are named in the facts on this page. What the facts do describe is a particular pattern of symptoms on a particular kind of tree.

Start with the tree itself, because peach leaf curl typically affects only peach and nectarine trees. Next, look at new leaves and shoots, which redden and pucker with this disease. Then check whether the leaves are thicker than normal as well as puckered.

Deformed areas that are red to yellow at first and later brown fit the description. Powdery gray spores or yellowing on the leaves may also be present. Shoots that are thickened, stunted, and distorted point the same way.

Timing gives another clue, since cool, wet weather when leaves are first opening favors the disease. Think back to the weather: wetness from rain, dew, or irrigation lasting more than 12.5 hours below 61 °F (16 °C) is what infection needs. Fruit with a corky, cracked surface is uncommon but belongs to the same list of symptoms.

Treatments

Plant resistant peach and nectarine varieties where possible, instead of relying on fungicides. Prune trees in fall, before applying any fungicide, to reduce the number of spores overwintering on the tree. On severely affected trees, maintain tree vigor by thinning fruit later in the season. You can also maintain vigor by irrigating during drought and fertilizing with nitrogen by mid-June. Avoid overstimulating the tree.

For an organic option, use a fixed copper fungicide such as copper soap (copper octanoate) or a copper ammonium product. Horticultural oil used alone is not effective against this disease. Combine it with a copper spray to increase effectiveness.

The synthetic fungicide chlorothalonil is the only other noncopper fungicide available, and it can be used as an alternative to copper. Apply a single fungicide treatment, copper or chlorothalonil, in fall just after leaves have fallen. You can also apply it in spring, with the application made before bud swell. A second late-winter application before bud swell can be considered. Do not apply fungicides during the growing season, because they will not be effective.

The pruning step comes first: prune in fall before you apply any fungicide. Remember that resistant varieties are the first option listed, ahead of fungicides. The product label is the legal instruction, so follow it for the crop and site you are treating. This page gives no dose, rate, dilution, or spray interval.

Prevention

Where possible, choose resistant peach and nectarine varieties when you plant. Pruning in fall can reduce spore numbers, and it should come before any fungicide is applied. The fungus overwinters on twigs and buds and survives the dry summer as spores.

Watch the weather as leaves open, because cool, wet weather at that stage favors the disease. Infection needs wetness from rain, dew, or irrigation lasting more than 12.5 hours at temperatures below 61 °F (16 °C).

On trees that have been severely affected, maintain vigor by thinning fruit later in the season. You can also irrigate during drought and fertilize with nitrogen by mid-June, while avoiding overstimulation of the tree. Fungicides applied during the growing season will not be effective. Fall and spring are the windows given for fungicide timing, with spring applications made before bud swell.

Plants most often affected

This page describes peach leaf curl, a fungal disease. It typically affects only peach and nectarine trees. New leaves and shoots on an affected tree redden and pucker. Affected shoots become thickened, stunted, distorted, and often die. Leaves also become puckered and thicker than normal.

• Black Cherry
• Cherry Plum
• Sweet Cherry