What are the specific-effective fungicides for grape rachis brown blight?
Before the young buds sprout, spray 3-5 degrees Baumé lime sulfur mixture, or 45% crystalline lime sulfur 30-fold solution, 0.3% sodium pentachlorophenate 1-2 times; before and after flowering, spray 75% chlorothalonil wettable powder 600-800-fold solution, or 70% mancozeb wettable powder 400-600-fold solution, or 40% captan wettable powder 500-fold solution, or 50% iprodione wettable powder 1500-fold solution; when the disease begins, spray daminozide 500-fold solution.
I. Symptoms of grape rachis brown blight
Grape rachis brown blight mainly damages the young rachis tissue of the grape cluster. In the early stage of the disease, brown water-soaked spots first appear on the branching rachis of the young cluster, and after rapid expansion the rachis turns brown and necrotic, and the berries lose water, wilt or drop. When young berries are infected, only small round dark brown spots 2 mm in diameter form on the epidermis; as the berries continue to enlarge, the surface of the lesions becomes scab-like, and when the berries grow to medium size, the scabs fall off and the cluster also shrinks.
II. Transmission routes of grape rachis brown blight
The following spring, from bud break to the flowering stage, conidia invade; after lesions form, the diseased parts again produce conidia, which spread by wind and rain and cause re-infection. If the flowering period in early spring is cold and rainy, the young tissue (rachis) persists for a long time and lignifies slowly, the plant is weak, and the pathogen spreads rapidly; as the rachis ages, the disease gradually stabilizes. Old trees are generally more susceptible than young trees; insufficient fertilizer or an imbalanced nitrogen-phosphorus ratio aggravates the disease, and the disease is severe in low-lying, poorly ventilated and poorly lit, and enclosed environments.
III. Grape varieties susceptible to the disease
Highly resistant varieties include Longyan, Muscat of Alexandria, Campbell Early, Missouri, and Muscat Hamburg, which almost never develop the disease; next are Beichun, White Banana, Black Hamburg, etc.; susceptible varieties include Red Banana, Red Perfume, Black Olympia, Red Fuji, and Kyoho, which is the most susceptible.