Sexual stages of grape black rot pathogen: Staphylococcus aureus is a fungus belonging to the subdivision Ascomycota.
Asexual stage: Phytophthora black rot on grapes is a fungus belonging to the subphylum Deuteromycotina. It mainly damages fruits, leaves, petioles and new shoots. When nearly mature fruits are infected, they initially appear as small purple-brown spots that gradually expand, with brown edges and a slightly sunken gray-white center. The diseased part continues to expand, causing the fruit to become soft and rotten, shrinking and turning into black or gray-blue stiff fruit with obvious edges and corners. The diseased fruit is covered with clear small black spots, which are the pycnidia or asthecia of the fungus. On infected leaves, small reddish-brown nearly round spots appear between the veins, with a diameter of 2 to 3 mm. After the lesions expand, the center is gray-white, the outside is brown, and the edges are black. There are many small black spots on them, arranged in a ring along the lesions. Infected new shoots show dark brown oval slightly sunken spots with many small black spots on them. The symptoms of this disease are similar to those of house blight. House blight mainly damages fruits and rarely damages leaves. In addition to damaging fruits, black rot also damages new shoots, leaves, tendrils and petioles.
1. Occurrence pattern
The black rot fungus mainly spends the winter on the fruit with ascospores, and can also spend the winter with conidia. In summer, the ascospores are spread by wind and rain, and can germinate and invade if there is suitable water and humidity. It takes about 36 to 48 hours for spores to germinate, and about 10 to 12 hours for germination at 22 to 24°C. The incubation period on the fruit is 8 to 10 days. Conidia are very viable. From August to September, the weather is hot and rainy and the disease is serious during the near-maturity period. In the south, its growth and decline pattern is similar to that of white rot.
2.Characteristics and identification methods
After the fruit is damaged, small purple-brown spots will appear in the early stage of the disease. After gradually expanding, the edges will be brown, the center will be gray-white, and slightly sunken. The affected fruit will become soft and rotten, and then become a dry, shrunken fruit with obvious edges and corners that are not easy to fall off. Many small black granular protrusions appear on the diseased fruits, which are the pycnidia or asthecia of the fungus. When the leaves become infected, small reddish-brown spots appear initially, and gradually expand into nearly circular lesions, with a diameter of up to 4 to 7 cm. The center is gray-white, the outer edge is brown, and the edge is dark brown. There are many small black protrusions on them, arranged in a ring. . Brown oval lesions appear on the injured areas of the new shoots, with a sunken center and small black granular protrusions. The main morphological differences between black rot and house blight are: the conidia of house blight are narrower and longer than those of black rot, and the ascospores are larger than those of black rot.
3. Use pesticides
(1)Desenzinc
Dosage form: 65% wettable powder.
Control period: Before flowering, after flowers fade and during fruit expansion period, use alternately with other fungicides once every 10 to 15 days, and control 2 to 3 times in a row.
Instructions: Use 30 grams of 65% wettable powder, add 15 kilograms of water, dilute it to a 500-fold solution, stir and spray evenly.
Precautions: It should be used in the early stage of the disease to achieve preventive effect; it cannot be mixed with copper preparations or alkaline drugs; safety precautions should be paid attention to when using medicine. Place it in a cool, dry and ventilated place. It will decompose when exposed to moisture and rain. Keep it away from food and feed, and out of reach of children.
(2)Chlorothalonil
Dosage form: 70% wettable powder.
Control period: Before flowering, after flowers fade and during fruit expansion period, use alternately with other fungicides once every 10 to 15 days, and control 2 to 3 times in a row.
Instructions: Use 30 grams of 70% wettable powder, add 15 kilograms of water, dilute it to a 500-fold solution, stir and spray evenly.
Precautions: Chlorothalonil cannot be mixed with alkaline pesticides such as lime sulfur mixture and Bordeaux mixture; this product should be protected from moisture and sun, and stored in a cool, dry and ventilated place. It is strictly prohibited to mix with food, seeds and feed. Keep away from children. Waste packaging after use should be properly disposed of.
(3)Carbendazim
Dosage form: 50% wettable powder.
Control period: Before flowering, after flowers fade and during fruit expansion period, use alternately with other fungicides once every 10 to 15 days, and control 2 to 3 times in a row.
Instructions: Use 25 grams of 50% wettable powder, mix with 15 kilograms of water, dilute to a 600-fold solution, stir evenly and spray.
Precautions: Carbendazim can be mixed with general fungicides, but when mixed with insecticides and acaricides, it should be mixed and used. It should not be mixed with alkaline agents. Long-term single use of carbendazim can easily cause bacteria to develop resistance, so it should be used in rotation or mixed with other fungicides. During soil treatment, it is sometimes decomposed by soil microorganisms and reduces the efficacy of the medicine.
(4) Arsine · Zinc · Thiram
Dosage form: 50% wettable powder.
Control period: Before flowering, after flowers fade and during fruit expansion period, use alternately with other fungicides once every 10 to 15 days, and control 2 to 3 times in a row.
Instructions: Use 15 grams of 50% wettable powder, add 15 kilograms of water, dilute it to a 1000-fold solution, stir and spray evenly.
Precautions: Do not mix with agents containing copper, mercury, or aluminum; this agent contains thiomearsine, which is prone to phytotoxicity, so care should be taken to control the dosage.
