Symptoms
1. Powdery mildew: After the leaves are infected, a layer of white or grayish white powdery mildew is produced on the surface of the leaves, which is the hyphae, conidiophores and conidia of the pathogen. When the powdery spots spread to the entire leaf surface, the leaves turn brown and scorch. When the new shoots are infected, many brown reticular patterns appear on the epidermis, and sometimes the branches and vines are difficult to mature. When the fruit stalks and panicle stalks are infected, the texture becomes brittle and it is very easy to break. When the fruit is infected, it stops growing and sometimes becomes deformed. When it rains a lot, the diseased fruit is prone to longitudinal cracking, the flesh is exposed, and it is very easy to rot.
2. Downy mildew: When the leaves are affected, the leaf surface initially shows small oil-soaked spots, which expand to yellow-brown. When the environment is humid, a layer of white mold-like substances, namely the spore stalks and spore sacs of the pathogen, will appear on the back of the spots. After the young shoots, spike axes, and petioles become infected, the oil-soaked spots quickly turn into yellow-brown depressions. When it is humid, the diseased parts also produce a rare white mold layer. The diseased shoots stop growing, twist, and even die. When young fruits are infected, the fruit surface turns gray-green in the early stage, covered with white mold layers, and the diseased fruits turn brown and dry up and fall off in the later stage.
Differences between grape downy mildew and powdery mildew
1. After powdery mildew infection, both leaf veins and leaf flesh will be infected; while after infection with downy mildew, the leaf veins are clearly visible.
2. Powdery mildew spores are generally seen on the front of the leaves; while downy mildew spores are generally seen on the back of the leaves.
3. The shapes and infection symptoms of powdery mildew spores and downy mildew spores are different. The spores of powdery mildew pathogens are almost like ivory yellow powder, densely spread on leaves and fruits; while the spores of downy mildew pathogens are more upright and white in color.
4. Powdery mildew usually occurs seriously in relatively dry weather. The disease starts on the front of the leaves in the early stage of the disease. Generally, the diseased leaves will not be necrotic, but the leaves are covered with white powder. In severe cases, the leaves will turn yellow or dry up. The powdery mildew on the fruit is generally covered with a thin layer of powder, which causes the fruit to dry up in the later stage; downy mildew usually occurs in rainy seasons, mainly yellow angular spots appear on the front of the leaves, and there is generally no mold layer on the front. Once the mold layer appears on the back, the front has obviously appeared yellow angular yellow spots. In severe cases, the whole leaf dies. Downy mildew has the characteristics of rapid development, high difficulty in prevention and control, and serious damage. The mold layer of downy mildew on the fruit is frosty, which is easy to cause fruit dryness and necrosis.
5. After powdery mildew is applied on the fruit, it will be wiped off by hand. The surface of the fruit will have yellow-brown net patterns. It mainly harms the front of the leaves. In severe cases, it will turn grayish white later. However, powdery mildew will gradually die once the relative humidity is 90%. Downy mildew starts from the back of the lower leaves. After the fruit is infected, a layer of white flocs will be attached to it early. Even if it is controlled by medicine, the flocs will be removed. The grapes will change color and ripen early, become soft, and fall off.
Comprehensive prevention and control
1. Powdery mildew prevention and control technology
(1) Combine pruning, cut off diseased vines, diseased leaves, diseased buds, and diseased fruits, and eliminate or reduce the source of pathogens.
(2) Strengthen field management, timely pinch and tie vines, cut off side shoots, make branches and vines evenly distributed, maintain ventilation and light transmission, and reasonably balance fertilization to prevent and control excessive growth of branches and vines.
(3) Before flowering, after flowering and before bagging are the key periods for powdery mildew prevention and control. Appropriate measures should be taken according to the local climate characteristics, cultivation methods and the occurrence of diseases in the previous year, combined with the prevention and control of other diseases. The available control agents include: carbendazim, myclobutanil, difenoconazole, ethiprole, etc. When powdery mildew occurs seriously, increase the dosage or mix them, spray once every 3-5 days, and apply them continuously for 2-3 times. At the same time, pay attention to sufficient water consumption.
Strengthen cultivation management, and create a good orchard ecological microclimate (especially in facility cultivation) through the regulation of water and temperature to limit the occurrence of diseases. At the same time, increase the application of organic fertilizers, phosphorus fertilizers, potassium fertilizers and trace element organic activated nutrient fertilizers, appropriately reduce the application of nitrogen fertilizers, and improve the disease resistance of the plants themselves.
2. Downy mildew control technology
(1) Strengthen orchard management. Collect diseased leaves and fruits, cut off diseased shoots, burn or bury them. The work of sweeping fallen leaves should be done in the early morning before the dew dries up, so that the leaves are not easily broken. During the growth period, attention should be paid to drainage and summer pruning; the trellis should be raised to more than 60 cm above the fruiting part, and unnecessary branches and vines that are too close to the ground should be cut off as much as possible to reduce ground humidity and reduce the incidence of diseases. Control nitrogen fertilizer, increase the application of phosphorus, potassium, and micro-fertilizers to promote the robustness of branches and leaves and improve the disease resistance of plants. For varieties with vigorous growth, it is advisable to use trellises, or adopt "high, wide, and vertical" shaping to ease the growth of branches and vines and improve ventilation and light conditions.
(2) Spraying for prevention and control. Use 1000 times diluted cymoxanil hydrochloride, spray once every 15 days or so, which has an excellent effect on the prevention and control of grape downy mildew. Spraying with 400-500 times diluted 50% zinc thiamethoxam wettable powder, or 500 times diluted 64% alum wettable powder, etc., all have good results.
