While northern Illinois is not an area where peaches are grown commercially, there are many home gardeners who do grow peaches. Peach leaf curl is a fungal disease of peaches and nectarines and it has been more prominent in Northern Illinois in recent years. While it is primarily a leaf disease, it can impact fruit production and the overall health of the tree. The disease can be severe in years with a rainy spring. A wet spring can lead to defoliation in the early part of the season. This weakens the tree and can lead to infection by other diseases, winter injury, and a reduced crop in the following year.
Disease symptoms begin in spring on expanding leaves. The leaves will become thickened and often severely distorted along the midvein. The distorted areas are often noticeable because they will be brightly colored with pink, red, and purple colors. Later, as spores are produced, the leaf surfaces will turn gray or have a powdery appearance. The leaves will eventually turn yellow and fall off. Peach leaf curl can also infect flowers, developing fruit and young shoots. Infected flowers and fruits often fall very quickly and may go unnoticed. Infected shoots will appear swollen.
Spores of Taphrina deformans, the fungus that causes peach leaf curl, overwinter on the buds and twigs of the host tree. Germination of the spores in spring is dependent on rainfall. Frequent periods of rain in spring, as peach and nectarine buds are opening, will lead to infection. When rain does not occur, then little or no infection will occur. Infection generally will not occur later in the season as only young plant tissues are susceptible. New spores produced on infected growth will be spread to twigs and buds by wind and rain. These spores will remain dormant until the following spring.
Cultural management is aimed at keeping a tree vigorous and healthy. Avoid excessive fertilizer as this can over-stimulate growth on the tree. Water trees in times of inadequate rainfall to minimize stress from drought.
Fungicides are available to treat peach leaf curl. Timing is important in the application of a fungicide. A single application of a fungicide can be made in the dormant season late fall or very early spring before buds swell. Applications made after the buds open will not be effective. If the tree is being grown for edible fruit, the fungicide selected should be labeled for use on trees producing edible fruit.