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Peach Leaf Curl Epidemiology and Control

Leaf curl on Redgold
Plant & Pest Advisory - February 28, 2012
Norman Lalancette, Ph.D.,
Specialist in Tree Fruit Pathology

Peach and nectarine leaf curl, caused by the plant pathogenic fungus Taphrina deformans, is typically not a difficult disease to control in the eastern United States. However, if inoculum levels are high, environmental conditions favor infection, and/or control methods are sub-par, then severe defoliation and stunting can occur. This year, unusual weather patterns may also play an important role in leaf curl development.

Infection. Taphrina deformans principally overwinters as spores on the bark surface; the pathogen may also be found in old infected leaves. Initial infection occurs during bud swell in late winter when spores are disseminated by water to buds with loose scales. Additional infection can occur between bud-break and petal fall. Once the pathogen enters leaf tissue, it stimulates rapid cell division and enlargement, resulting in thickened, curled, and puckered leaves. These “tumor-like” areas on the leaves often have a red discoloration. Eventually, the leaves drop or sometimes remain attached, turning brown.

Environment. Recent research results from Italy have provided details on the effects of temperature and moisture on foliar infection (1). At near optimum temperatures, infection began after a minimum of 12 hours wetness and increased steadily until 48 hours of wetness. Longer durations of wetness did not increase disease levels.

In these studies, duration of surface wetness was the primary moisture determinant for infection. If the wetness period was caused by rain- fall, the amount of precipitation did not influence the severity of infection. Wetness periods from dew or fog were often too short for infection.

Air temperature during the wetness period needed to be less than 61°F for foliar infection to occur. The amount of infection increased as temperatures decreased to 41°F. The maximum amount of shoot infection (45%) was observed at 41°F. Lower temperatures were not examined to determine at what point infection no longer occurred.

Control. A single fungicide spray in fall, after leaf drop, or in late winter just prior to bud-swell, will in most cases provide sufficient control. The recommended fungicides are ziram or chlorothalonil (Bravo, Echo, etc.). Both of these fungicides have provided near 100% control in studies on ‘Redgold’ nectarine at the RAREC; non-treated trees had 39% bud infection.