Peach Leaf Curl

Leaves produced in spring are thickened, curled, and colored red or yellow instead of normal green. Severely affected shoots die. Irregular, reddish lesions are sometimes seen on fruit. Badly diseased leaves fall by early summer, and repeated infections debilitate trees and kill branches.

After fall and winter rains, spores (blastospores) of the fungus may be observed as a white bloom on the surface of leaves and be found on twigs, buds, and inbetween bud scales.

Taphrina deformans survives on tree surfaces and buds and is favored by cool wet weather during spring. The pathogen most likely survives the warm, dry summer period as ascospores. With fall and winter rains, the ascospores germinate and form numerous budding blastospores. Tree to tree spread of the pathogen occurs by airborne ascospores, which can move longer distances or by blastospores that are disseminated in splashing water. Leaves and the occasional fruit infections occur only on young plant tissue.

Peach leaf curl can be a serious problem, especially on many of the low-chilling varieties and when spring weather is unusually wet. Annual management is recommended. To successfully control the disease, treatment timing is crucial. This disease is usually kept under control with a dormant fungicide application, but in wet years more than one spray application may be needed.

Spraying with Bordeaux mixture or copper is acceptable in an organically certified crop.

Most copper products have long residual activity, even during prolonged wetness. Therefore, one application in the dormant/delayed dormant period is sufficient except in areas of high rainfall or where leaf curl has become an increasing problem. In such cases, an added application at delayed dormancy in late winter or before bud swell is recommended. Recently, formulations of fixed coppers have been developed with reduced metallic copper equivalent (MCE). Residual activity is very important to control peach leaf curl and these products, when lower rates are used (e.g., 1.2 to 2.1 lbs/A MCE for reduced MCE fixed coppers, compared to 3 to 5 lbs/A MCE for fixed coppers or even 8 to 10 lbs/A MCE for basic copper sulfate), have not been as efficacious over long rainy winter seasons.

If using the newer reduced MCE products

• always use the upper label rate,
• consider using a sticker or winter oil as an adjuvant to increase persistence, and
• plan to make two applications.

Several other fungicides that are equivalent or even more effective than copper for managing peach leaf curl are ziram, chlorothalonil (Echo or Bravo), and dodine (Syllit) when applied at the optimal time. Ziram is most effective.

1. Apply in late November/early December after most leaves have fallen from trees to ensure excellent coverage of branches, stems, and buds and before significant late fall and winter rainfall occurs. (This spray will also control shot hole (Wilsonomyces carpophilus).
2. Apply an additional January/early February treatment if high rainfall occurs in December and early January.
3. In addition to January/early February treatments, apply during pre-bloom (at bud swell or two weeks before bloom) if high rainfall occurs in February.

To increase fungicide persistence of the materials, use an adjuvant such as an oil or a sticker.