Pear rust, scientifically known as Gymnosporangium sabinae, is a disease caused by a rust fungus. This fungus alternates its hosts between pear trees and juniper species. It overwinters on junipers during the winter and, with the spring rains, spreads over distances ranging from several hundred meters to a few kilometers to infect pear leaves. After an incubation period of about 8–9 days, visible symptoms usually appear in around a month. From the tubular structures on the underside of pear leaves, new spores are released and carried back to junipers, thus sustaining the infection cycle.
The disease spreads especially quickly during the rainy season, when leaves remain wet for long periods. High humidity, rain, and wind all contribute to spore dispersal, and if juniper trees are located near an orchard, the risk of infection rises significantly. The effective spread distance is roughly 1.5 km, with severity increasing the closer the pear and juniper trees are to each other.
Infected pear leaves first show small yellow to orange spots. If not controlled early, the spots enlarge and eventually merge into blotches that cover much of the leaf surface. In severe cases, the disease spreads to fruit and new shoots as well.
When pear trees are affected by scab, photosynthesis declines sharply, leading to premature leaf drop and overall tree weakness. Fruit quality also suffers: sugar content, size, and coloration are reduced, and blemishes appear on the skin, significantly lowering market value. In severe cases, fruit drop occurs.
If the disease is not effectively controlled, the damage continues into the following year. The tree’s winter hardiness weakens, and the number of flower buds decreases, reducing yield in the next season. In other words, this disease is not just a one-year problem but a serious threat that can cause losses over two or three consecutive years.
Preventive control is crucial because infections often occur before symptoms become visible. Regular treatments are necessary, with special focus during the rainy season when conditions favor the spread. In the JADAM method, control can be achieved by applying JADAM Microbial Pesticide (JMP) with the addition of JADAM Sulfur (JS). The addition of JS provides strong insecticidal and fungicidal effects.
Although pear rust is notoriously difficult to manage, as shown in the referenced video, successful control has been achieved with this method. It takes time to confirm the effectiveness: when the spots on leaves turn black and become dry and brittle, it indicates that control was successful—but this visible change can take several months. For best results, spraying should be done during strong sunlight hours.
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