Taphrina deformans (peach leaf curl)

Symptoms appear about 1 month after flowering starts. Leaves are thickened and distorted (puckered, curled) and green to bright red, depending on variety (Wilson and Ogawa, 1979). Whole shoots are affected when the infection becomes systemic in the growing tip, causing lateral shooting or 'witches broom'. Flowers and fruit surfaces may be similarly affected, with heavily diseased trees having a dramatically different appearance to healthy trees. When diseased leaves are about to release ascospores their surfaces develop a silvery-white 'bloom'. Later these leaves turn black, die, fall and are replaced by new leaves. Leaf blackening coincides with higher daytime temperatures. Areas of bark are also blackened where systemic shoot infection was present. Fresh leaf curl symptoms can reappear on new autumn shoot growth in vigorous varieties.

No host immunity is known, resistance is present in a few varieties and susceptibility varies between varieties, but varietal resistance is not currently used to control leaf curl. Chemical control is very effective if sprays are applied at leaf fall and/or just before bud break. A single spray after leaf fall is used in drier peach growing regions, but in wetter regions, several leaf-fall copper-based sprays (copper oxychloride, cupric hydroxide, Bordeaux mixture) and one or two bud-movement sprays of ziram, thiram, copper-based compounds and other fungicides are used to effectively control the disease. The development of resistance to copper-based fungicides was demonstrated in T. deformans by Cheah et al. (1993).

T. deformans has little economic impact on commercial orchards where spraying occurs, but if spraying is not carried out, total yield loss can occur due to extensive defoliation, with eventual tree debilitation, stunting and death.