Pear scab is caused by an ascomycete fungus and mainly damages leaves, petioles, fruits, fruit stalks, flower stalks, buds, new shoots and other parts. Severe leaf damage can easily lead to early defoliation, and fruit damage can easily cause fruit cracking and early fruit drop, seriously affecting economic benefits.
1. Occurrence rule
Scab overwinters in diseased shoots, diseased leaves and bud scales with hyphae or conidia. In the following year, conidia or ascospores produced by ascospores formed by hyphae are used as the primary infection source, and spread by wind and rain, the first disease occurs at the base of the shoot buds, and then the infection continues to expand.
2. Characteristics and identification methods
After the buds germinate in spring, small black spots appear on the white part of the elongated base of the bud scales, and a black mold layer will appear on the lesions later. The damaged buds and scales have many hairs and do not fall off. In severe cases, the bud scales will crack and die. The leaves are susceptible to the disease, mostly on the main and lateral veins of the back of the leaf. At first, it is a round or oval or irregular light yellow spot, and then black mold is formed on the lesion, which is radial. In severe cases, it can spread to the whole leaf and cause the leaves to fall off. . When the petioles, flower stalks, inflorescences and fruit stalks are damaged, the symptoms are generally the same. Small black spots or oval spots appear on the stalks, which gradually expand and produce black mold layers. The diseased part is sunken, causing early leaf, flower and fruit drop. The new shoots are damaged, and the base of the young shoots initially turns yellowish brown, and finally the young shoots die. When young fruits are susceptible to the disease, small light brown round lesions will appear on the surface of the fruit, and black mold will appear on the surface. The diseased parts will be sunken and cracked, and they will easily fall off prematurely. In the later stage of fruit infection, round or nearly round black lesions of varying sizes appear on the fruit surface. The surface is dry, hard, rough, and there is very little mold layer. Before harvest, the fruit is susceptible to the disease. Small light yellow lesions appear on the fruit surface, with irregular edges, mostly in the shape of awns, and no mold layer.
3. Use pesticides
(1) Flusilazole
Dosage form: 40% EC
Control period: The first spraying is carried out at the dew bud stage; the second spraying is carried out 8 to 12 days after the flowers fall.
Usage method: 10-year-old trees should be sprayed at a dosage of 15-20 kg each time, and the dosage should be increased for trees with large crowns as appropriate.
Precautions: Every time the pesticide is applied, the leaves and fruit surface should be uniformly coated. Rainfall 3 to 4 hours after application will not affect the efficacy of the drug; do not splash the liquid on the eyes and skin, and wash your hands and face with soap immediately after use.
Dosage form: 50% WP
Control period: The first spraying is carried out at the dew bud stage; the second spraying is carried out 8 to 12 days after the flowers fall.
Usage method: Mix 18 grams of 50% wettable powder with 15 kilograms of water to prepare an 800-fold solution, stir and spray evenly.
Precautions: It can be mixed with a variety of fungicides, acaricides, and insecticides, but it should be mixed and used immediately. Do not mix it with copper preparations or alkaline agents; use it alternately with other disease-preventing pesticides to avoid the development of drug resistance; avoid direct contact between the liquid and skin and eyes.
