Leaf curl

Peach leaf curl is a fungal disease caused by Taphrina deformans that affects peaches and nectarines. If untreated, it is one of the most serious and common diseases of these crops.

Disease identification

Leaf curl symptoms appear early in the season, about one month after flowering starts. The infection will appear on younger leaves first and the infected portions can be pink to red. These areas become thickened and do not expand at the same rate as healthy leaf tissue. This leads to the characteristic curled appearance of this disease.

Whole shoots can be infected, becoming swollen, stunted and distorted. They will be pale green to yellow and might exude gum. Often the result is death of the shoot. When this damage affects leaders, lateral branching can occur, leading to ‘witches’ brooms’. Young trees are particularly susceptible to shoot infection.

Infected fruit has raised, irregularly shaped and roughened areas on the skin surface, which might redden before healthy fruit shows any colour change.

Leaf curl is often seen in the top of the canopy, where spray coverage might not have reached.

Disease cycle

The disease spreads by fungal spores being splashed onto emerging leaves and is most severe if cool, moist weather occurs during blossom to shuck fall. If a severe infection occurs and the disease is not controlled, further disease cycles can occur later in the spring.

Peach leaf curl is favoured by a cool, wet spring around bud swell followed by warm, humid conditions, which bring about rapid growth. The optimum temperature range for fungal growth is between 20 °C and 26 °C. After the initial infection, leaves will curl and become severely distorted. Leaves then tend to turn yellow and fall, causing new tissue to replace fallen leaves. The energy required for this new growth reduces fruit set and weakens trees.

Monitoring

Correctly timing protectant sprays in early spring (particularly copper-based fungicides) is vital for controlling the disease. Monitor bud development in late winter to early spring to ensure correct spray timing according to label instructions. Monitor and record the incidence of leaf infection.

Management

Cultural and physical: where leaf curl has been a serious problem, it is important to put more effort into maintaining tree vigour. Thin more fruit than usual, ensure adequate irrigation and apply extra nitrogen fertiliser. Controlling the disease is particularly important in young trees as an infection can severely distort growth.

Biological: there are no known biological control agents for peach leaf curl. However, copper sprays provide effective control and some copper-based fungicides have been approved for use in organic production systems.

Chemical: check the APVMA PubCRIS database for registered controls (https://portal.apvma.gov.au/pubcris). Where necessary, only one application of a fungicidal spray is sufficient to control leaf curl. This application must be thorough and correctly timed at early bud swell. The ends of limbs and twigs must be well sprayed. Spray before the buds burst or little control will be achieved and the spray might injure the young growth.