How to prevent grape black spot disease?
Reader Zeng Wenyan: When I arrived on National Day, I was gifted a bunch of flowers by my friends. However, the flowers had only been in the vase for three or four days, and there were already many in the room. This situation often happens when people receive multiple bouquets, and I'd like to learn more about how to properly care for cut flowers.
There seems to be some confusion in your message. Reporter: Ms. Zeng, how are you?
Many families purchase flowers or receive them from relatives and friends during festivals to create a festive atmosphere. There's a lot of information available on how to properly care for fresh cut flowers. Experts from the Municipal Bureau of Parks have provided answers to your questions.
1. Identifying Grape Black Spot Disease, also known as Dwarf Disease, is commonly referred to as "Black Spot." It is a significant disease affecting grapes. The main symptoms include:
(1) Initially, small brown spots appear at the site of injury, which later develop into round spots with a tan color, ranging from 1 to 4 mm in diameter. The center becomes gray, and the affected tissue dries out and becomes hard, eventually forming a hole. Young leaves often become distorted and shriveled after infection.
(2) The fruit is not typically infected early on, but as it starts to ripen, brown round spots appear. The center of these spots turns gray and white, slightly sunken, with reddish-brown or purple edges resembling "bird eyes." These small lesions can merge into larger ones, and the affected areas may harden or crack. Infected grapes tend to be small, sour, and unsuitable for consumption.
(3) New shoots, petioles, pedicels, and tendrils initially show small brown dots that later turn grayish-black. A central depression forms, leading to dry, ulcerated wounds, which can cause severe drying or even death of the plant parts.
2. Pathogen Infection: The pathogenic bacteria overwinter in diseased tissues, and the primary sources of infection are the mother plants and tendrils. When environmental conditions are favorable, the pathogen produces conidia, which spread through wind and rain. The initial infections occur on new shoots and young leaves, and then move to fruits, tendrils, and other parts. The incubation period after spore infection lasts 6 to 12 days. The disease typically begins in late May to early June when temperatures rise, and it peaks between mid-June and early July. The disease stops developing after October. During the grape growth cycle, it often appears in the flower buds.
3. Control Methods:
(1) Seedling Disinfection: Grape Black Spot Disease mainly spreads through infected seedlings. Therefore, strict inspection of all seedlings and planting material is essential. Any seedlings suspected of being infected should be disinfected before planting.
(2) Orchard Sanitation: Maintain cleanliness in the vineyard by pruning and removing diseased leaves, fruits, and vines to prevent the spread of the disease.
(3) Spraying Protection: Apply a 3–5° Baumé solution of lime sulfur before bud break. During the growing season, spray once every 15 to 20 days, starting from the emergence of leaves until the fruit reaches one-third of its size. You can use 50% carbendazim wettable powder diluted 1,000 times, or 80% zoxamide wettable powder diluted 600 times. Consistent spraying helps control the spread of the disease effectively.
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