How to Treat Grape Diseases? A Detailed Guide to Scientific Control Methods

Grapes occupy an important position in world fruit production. During cultivation, grape pests and diseases greatly affect the growth and development of the plants as well as yield and quality. So, how do you treat grape diseases?

1. Grape anthracnose

Symptoms: Grape anthracnose can infect fruits, canes, leaves, tendrils and other parts. Brownish small round spots appear at the infected sites, gradually enlarge and become sunken; concentric ring-like, nearly circular lines form on the lesions, along with neatly arranged small black dots. These black dots are acervuli. In wet weather, pink gelatinous masses of conidia ooze from the acervuli, which is a characteristic feature of the disease. The lesions can expand to cover the entire fruit surface; diseased fruits gradually dry and shrink into mummified fruits, and sometimes an entire cluster shrinks into a mummified cluster.

Control measures: Spray fungicides starting in late April in the south and late May in the north, then generally spray once every 10-15 days. You can spray 80% thiophanate-methyl plus zineb at 700-800 times dilution, 50% chlorothalonil at 600-700 times dilution, or 50% thiram or mancozeb at 800 times dilution. In the south, where there is a lot of rain, add “6501” at 1500 times dilution or 0.03%-0.05% skin glue or other stickers to the spray solution.

2. White rot

Symptoms: On fruit stalks and cluster stems, light brown, water-soaked, nearly circular lesions appear first at the diseased sites; the diseased part rots and turns brown, and very quickly spreads to the berries. The berries turn brown, soft and rotten. Later, grayish-white small granular pycnidia form on the surface of the diseased berries and cluster stems, and diseased fruits fall off easily.

Control measures: In the north, after the vines are uncovered from the soil, spray 5 degrees Baumé lime sulfur mixture or 100 times dilution chlorothalonil; starting from the young fruit stage (early June), spray once about every 15 days as a preventive measure until harvest. In the south, focus on control during the inflorescence separation stage (late April to early May), 7 days after flowering, and half a month before ripening. The main fungicides include half-strength, equal-strength or double-strength Bordeaux mixture, 75% chlorothalonil at 800 times dilution, 50% carbendazim wettable powder at 700 times dilution, 70% thiophanate-methyl at 700 times dilution, or 50% thiram at 800 times dilution.

3. Downy mildew

Symptoms: Grape downy mildew mainly damages leaves, new shoots and young fruit. On affected leaves, small, light yellowish-brown, water-soaked spots with indistinct edges appear first; the lesions gradually expand into irregular or slightly round large yellowish-brown spots, up to 13 cm in diameter. The edges of the lesions are indistinct, and multiple lesions can join together to form large patches.

Control measures: Spraying should begin at the early stage of disease onset. In the north, it generally starts in early to mid-June, with spraying once every 15 days. 25% metalaxyl or domestically produced metalaxyl at 600 times dilution gives the best control effect; 40% fosetyl-aluminium at 300 times dilution, 90% fosetyl-aluminium at 500 times dilution, or 1:0.5:200 Bordeaux mixture also provide relatively good control.

4. Powdery mildew

Symptoms: The disease occurs on grapes. Green parts such as fruits, leaves and new canes can all be affected, but damage to the fruit causes the greatest loss. When fruit is affected, a layer of grayish-white powdery mildew first forms on the berry surface; after wiping off the white powder, the epidermis shows brown patterns, and finally the epidermal cells turn dark brown.

Control methods: Before bud break, spray 3-5 degrees Baumé lime sulfur mixture once; after bud break, spray 0.2-0.5 degrees Baumé lime sulfur mixture, or 50% thiophanate-methyl at 500 times dilution, or 70% thiophanate-methyl at 1000 times dilution, or 25% triadimefon wettable powder at 1000 times dilution.

5. Brown spot

Symptoms: Grape brown spot occurs in most grape-producing areas in China, with more occurrence in the rainy and humid coastal and Jiangnan provinces; in general, it is milder in arid regions or in years with little rain. Poorly managed orchards can experience heavy outbreaks in the later stage of rainy years, causing early defoliation, weakening the vines and reducing yield.

Control methods: In severely affected areas, combine control with that of other diseases. In June, spray equal-strength 200 times dilution Bordeaux mixture once; from July to September, spray 500 times dilution 50% carbendazim, 600-800 times dilution chlorothalonil, or 800-1000 times dilution 70% thiophanate-methyl alternately, once every 10-15 days. 65% mancozeb can cause phytotoxicity on some grape fruits, more obviously in the north, and the concentration used should be 1000-1200 times dilution.

“Prevention first, integrated control” is the basic principle of grape pest and disease control. In grape production, the dynamics of disease outbreaks should be observed at all times so as to prevent them in advance. Integrated control should be based on agricultural control, while at the same time, measures such as chemical pesticide control, biological control and physical control should be used rationally according to local conditions.