Apple rust is mainly harmful to leaves, but also can damage fruit, petiole, fruit stalk and new shoots. The main symptoms after onset are: orange-yellow part of the disease, thick and swollen tissue, yellow spots on the surface, black gradually, and yellow long hair on the lesion.
The blade is damaged, firstly, it produces an orange-yellow round lesion on the front side, which is lustrous; the posterior lesion gradually enlarges, and the periphery presents a yellow-green or red-brown halo. The lesion has orange-yellow convex small grain spots and secretes yellow-brown mucus; After the mucus is dry, the small spots turn black; and the lesions become thicker, the front is bulged, and the back is sunken; finally, the back of the lesions are many yellowish brown hairs. When there are many lesions on the leaves, the leaves are distorted and deformed, which is easy to turn yellow and fall.
The fruit is affected, the symptoms and development process are similar to those of the leaves, but only yellow long hairs are produced next to the small black spots. New shoots, fruit stalks, and petioles can also be affected, and the symptoms are similar to those of fruits, but most of them are spine-shaped lesions.
Pathogen and pathogenesis
Apple rust is a parasitic true disease , the pathogen is Yamada rust fungus, and its main host is cypress. The cypress is damaged, mainly producing yellow-brown to brown tumors (bacteria) on the branchlets. The pathogens overwintered on the main host, the cypress, with a nodular structure. In the spring of the next year, spores were produced by overwintering bacteria under high-humidity conditions. The spores were transmitted to the young tissues of apples through the airflow, and infested from the stomata to damage the leaves and fruits. After the onset of the apple, the spores are produced first (in the orange-yellow small spot), and the rust spores (produced by the yellow-brown long hair) are generated. The rust spores are transmitted through the airflow to infect the cypress, and in the cypress, and Wintering on the cypress. Therefore, the disease is not infected again, only once a year.
Whether rust occurs and how light and heavy it is is closely related to how close and close to the cypress is. If there is no cypress within 5000 meters around the apple orchard, there will be no rust. Under the premise of cypress, the rainfall before and after apple flowering is the decisive factor affecting the occurrence of disease.
Control technology
(1) Eliminate or reduce the source of initial infection: completely cut off the cypress within 5000 meters around the orchard, which can basically prevent rust. If you can't cut off the cypress around the orchard, you can pruning the cypress before the germination of the apple, completely cutting off the worms that have been overwintering on the cypress, and then destroying them centrally; you can also kill the overwintering bacteria on the cypress before the apple sprouts.
(2) Pharmacy protection apple tree: In the apple orchard, which has the disease condition and has serious rust in the past years, it can effectively control the rust disease by spraying the apples before the flowering, before the flowering, and after half a month after the flowering. The commonly used effective agents are 1500-2000 times of 12.5% ​​myclobutanil wettable powder and 3000 times of 25% tebuconazole wettable powder, and all have good control effects.
(3) bactericide protection 桧 :: When you can't cut 桧 ,, you can protect 桧æŸå–·. Generally, after the yellow-brown hair is produced from the back of the apple leaf, the spray is sprayed on the cypress, and after 10-15 days, it can be sprayed once again to basically control the damage of the cypress. The effective agent is administered with the apple. If 2500-3000 times solution of soft water is added to the drug solution, the effect of drug control can be significantly improved.
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