How to control peach leaf curl

Peach Leaf Curl: symptoms, prevention, treatment

Peach leaf curl is a fungal disease caused by the pathogen Taphrina deformans, which attacks the buds, leaves, fruits and young shoots of peaches, nectarines and almonds. It is one of the most widespread diseases of fruit trees, causing serious losses to growers in terms of yield and tree health.

What is peach leaf curl?

Peach tree leaf curl infects young leaves as soon as they sprout from the buds. It appears as red spots on young peach leaves in the spring. These spots gradually thicken and deform, creating the typical curly leaves that are emblematic of this disease. Later on, the color of the spots gradually changes to yellow to white, which is a sign of the production of a large number of spores that will further spread the fungus. This fungal disease thrives in wet and cold weather during the winter and spring months, especially while new leaves are sprouting.

The activity of this fungal disease decreases as soon as daytime temperatures rise above 77°F (25°C). It survives the summer period mainly in form of ascospores. Then, with the onset of cooler autumn temperatures and humidity, its activity increases again, as it produces a number of blastospores which will again produce spores to infect young peach buds in spring.

Infected peach leaves eventually turn brown and either remain on the tree or fall off. The diseased tree often grows a second wave of leaves, but this exhausts the tree and leaves it with insufficient vigour to produce fruit, generally weakened and susceptible to other diseases. More rarely, peach curl also attacks the young shoots or fruit of the peach tree. If this fungal disease is left uncontrolled, the peach tree gradually deteriorates and often dies after a few years.

Peach leaf curl treatment

1. Prevention

Peach curl can be largely prevented by selecting peach, nectarine and almond varieties resistant/tolerant to this disease. No variety is completely resistant, but the disease is milder in case of more resistant varieties.

Peach curl can also be alleviated by raking off fallen leaves, removing diseased and damaged peach branches and reducing the nitrogen content of peach fertilizer. For prevention, it is also advisable to get rid of peach trees affected by leaf curl in the neighborhood.

2. Control by fungicides

An effective and often used form of protection against peach curl is spraying with fungicide products containing copper, which is toxic to the peach leaf curl but has no adverse effects on plants and animals, including humans. Another alternative is treatment by organic fungicides, which, however, are more toxic to animals and microbial life.

When to apply fungicide spray against peach leaf curl

Fungicide sprays containing copper should be applied in spring just before the peach buds start to open. During the spring, experienced gardeners monitor bud swelling on their trees in order to estimate when the peach tree is about to sprout and apply a spray of a copper-based product just before this happens, when the bud covers are about to crack. The date of spraying is difficult to estimate because sprouting varies each season (usually from the end of January to the beginning of April, depending on the climate zone).

If the spray is well timed, one application is sufficient, but problems can be caused by rain washing away the spray before the peach buds sprout. A further timing obstacle is that the buds sprout faster on the tips of the branches compared to the lower parts of the branches. Therefore, it is recommended to spray several times in early spring. It is important to spray all the branches and buds from each side so that the product covers the tree completely and destroys all the curly leaf spot spores.

Autumn spraying after leaf fall is often recommended, but it is not as effective as a well-timed spring application, so it can be skipped if the disease is not severe.

What fungicides are effective against peach leaf curl?

Any product containing tribasic or basic copper sulfate, cupric hydroxide or copper oxychloride sulfate can be used for spring spraying against peach leaf curl. These substances are toxic to fungi and some bacteria, but are not dangerous to animals in normal concentrations. The cheapest home-made option of tribasic copper sulphate, can be prepared by mixing copper sulphate, hydrated lime and water in a 1:1:100 ratio. Treat trees with copper fungicide sprays only until the first buds have sprouted, as they could damage the young leaves. The dosage indicated on the product packaging should always be observed. Copper fungicides are approved for natural gardening.

Various fungicides made from organic compounds (”organic” here refers to chemistry rather than an all-natural product) are also effective against peach curl, but these can also be more harmful to animals, so they should be handled with more caution. These products can also be used on young leaves until peach flowers start to open. Thereafter, any fungicide application against peach curl is ineffective.

For organic growers, the use of natural fertilizers containing copper and zinc are available. These are designed to be sprayed directly on the buds and young leaves of the peach.

24.06.2022

Author: Daniel Weber