Peach leaf curl is the main fungal disease affecting this beloved fruit tree cultivar. We’ve already talked about the major pests of peach trees, and now it’s time to delve deeper into this issue. If not controlled preventively, this disease can compromise the entire annual production of our trees. Peach leaf curl is a sneaky disease; by the time it appears in spring, it’s usually too late to intervene. Organic peach treatments must be carried out during the fall-winter period. Only by acting preventively can we avoid the onset of infestations.
That being said, let’s get to know this peach disease better and see how and when to intervene to prevent damage.
What is Peach Leaf Curl?
Peach leaf curl caused by Taphrina deformans
Peach leaf curl (Taphrina deformans) is a fungus belonging to the Ascomycetes class. Its common name refers to its preference for peach trees. In English, it’s called “peach leaf curl.” This fungus is present in all Italian regions, but it causes the most damage in the North, where it finds ideal climatic conditions to thrive. During winter, the fungus is present on the plant’s surface, on the bark, and among the buds, in the form of blastospores, which are asexual spores. These spores multiply through budding even in very low temperatures. They can spread through heavy rains, which splash them from one part of the plant to another. This proliferation phase is called the saprophytic phase. Mild, humid, and rainy winters provide the ideal conditions for spore multiplication on the plant.
However, it’s not during the winter period that peach leaf curl causes damage. Attacks on different parts of the tree start occurring from the end of winter, especially at the beginning of spring. It is when buds break, and the first shoots emerge that the fungus enters its parasitic phase. Peach leaf curl is the most serious and problematic disease of the peach tree because it affects the plant’s green organs, such as shoots and leaves. Moreover, if the attack is severe and affects sensitive varieties, it can also damage flowers and fruits. The damage caused is irreversible; for instance, leaves dry and fall off after the fungus attack, significantly compromising both the current year’s and the following years’ production if not properly addressed. Let’s take a closer look at the various symptoms of this disease caused by the fungus.
Symptoms of Peach Leaf Curl
On Shoots
Peach leaf curl appears on young shoots between late winter and early spring. These shoots are attacked by the fungus when buds open. When the bud opens and the shoots emerge, they are already deformed. The small leaves appear as wrinkled masses, with the typical fleshy appearance. They also have noticeable color changes, ranging from yellow-orange to deep red. The young leaves are blistered and glassy in texture. Shoots affected by peach leaf curl cease their development and gradually dry out in the following months. If the fungus is present on the plant, the ideal conditions for infection occur during continuous wet periods lasting at least 24 hours. It’s essential to note that wetness here doesn’t only refer to rain but also to other phenomena like fog. Additionally, dry periods less than 4 hours cannot be considered an interruption of wetness. Another climatic factor is that during wetness, the average temperature must be below 15°C, and after wetness, it should be below 18°C. These conditions favor disease incubation. The incubation period varies from three weeks to ten days. Sole wetness is sufficient to guarantee infection only in the early stages of shoot growth. In later stages, when the shoot tip moves away from the bud scales, rain presence becomes essential for inoculation. If the attack occurs at this stage, without repeating in the following months, and if the plants are in good general condition, the tree may respond by producing new shoots in the summer. However, the stress due to the attack still compromises production.
On Other Green Parts of the Tree
Fruit affected by peach blister
The symptoms on fully developed leaves are very similar to those seen on shoots. Blistering, reddish coloration, and glassy texture can appear on fully formed leaves in spring and beyond. If the spring season is warm and dry, peach leaves are safe from infection. Prolonged and consistent rains should be avoided in spring to protect peach leaves from infection. Leaves are partially affected by the fungus, which doesn’t decisively compromise their elongation and development. However, the damage remains severe; affected leaves are stressed, have less energy, and eventually dry up or rot. Peach leaf curl can also attack open flowers, turning them into fleshy, deformed masses that eventually fall off. Lastly, the attack can occur on fruits, especially during the growth phase. Affected fruits show obvious signs, with wrinkled, blistered areas and abnormal orange-red discolorations. The areas affected by the disease stand out compared to the fruit’s normal texture. In these areas, rot and lesions caused by other fungal agents to which the fruit is more susceptible are likely to occur. Obviously, fruits affected by peach leaf curl do not ripen properly and are inedible. If the fruit is attacked early, in the post-setting phase, it immediately falls off.
Preventing Peach Leaf Curl: How and When to Intervene
Peach leaf curl is a disease that is prevented during the fall-winter period, in the fungus’s saprophytic phase. Therefore, in spring, when buds open, it might be too late to intervene. Let’s see how to act with entirely organic treatments. In organic farming, two classic fungicides, copper and calcium polysulfide, are used. We’ve already discussed the uses of copper in organic farming when talking about tomato downy mildew. We’ve also shown how to prepare Bordeaux mixture at home. We recommend reading the articles for more in-depth information.
Biological treatments with copper should be carried out at different times; let’s understand when.
First Organic Copper Treatment
The first intervention against peach leaf curl is necessary in November, at the latest in early December, when trees have shed all their leaves. Typically, intervention is done with copper oxychloride (available here) or Bordeaux mixture (which you can find here). This first biological treatment is very important and can be done in a single solution or in two interventions. By reducing the recommended dosage, two treatments can be performed 20 days apart.
Second Organic Copper Treatment
The second biological treatment is carried out at the end of the winter period, roughly between late January and mid-February, before buds open. In this case, propolis is added to copper to enhance its effectiveness and boost the plant’s natural defenses. Propolis is a natural product derived from beekeeping (a specific formulation for agriculture can be found here). The indicated biological treatments should be carried out on dry and not overly cold days. The plant should be uniformly wetted; you can use a classic backpack sprayer, like this one.
Alternatively, instead of the copper and propolis treatment, calcium polysulfide, a product permitted in organic farming, can be used. This substance is also effective as an insecticide, especially against scale insects.
Third (Optional) Organic Treatment
In the post-flowering period, if weather conditions favor infection, low doses of calcium polysulfide (2%) can be applied until the end of April.
Agronomic Prevention of Peach Leaf Curl
Peach leaf curl can also be prevented by implementing appropriate agronomic practices. First and foremost, if our trees were attacked by peach leaf curl in a season, proper pruning must be carried out. Infected crop residues must be removed from the orchard and burned. Pruning should be balanced every year to prevent excessive shoot development, which is the most susceptible part to peach leaf curl attacks. Lastly, it is advisable to prevent water stagnation, as it further encourages the fungus’s presence and disease spread.
