What fungicide should be used when grapes suffer from gray mold, downy mildew, and powdery mildew?

Although greenhouses and rain shelters are used, which can reduce disease occurrence to a certain extent, when environmental humidity is too high, grapes will still develop diseases, and with a little carelessness they will be infected with gray mold, downy mildew, white rot, black pox, white rot, and powdery mildew, and the most serious and most difficult to treat are gray mold, downy mildew, and powdery mildew. So what fungicide should be used when grapes suffer from gray mold, downy mildew, and powdery mildew?

1. Harm of gray mold

During the seedling-raising process, even if the film is fully covered and then a shade net is also covered, the seedlings inserted into nutrient cups are rarely infected with gray mold. When the same measures were used in Hunan, Chongqing, Sichuan and other places, large outbreaks of gray mold were found.

Yunnan is an area with strong sunlight, and the strong ultraviolet rays kill gray mold spores, thereby reducing the number of gray mold spores diffused in the air and making the damage milder. But in the middle and lower reaches of the Yangtze River, including Hunan, Chongqing, Sichuan, and even Jiangsu, Shanghai, Zhejiang, Jiangxi and other areas with little sunlight, gray mold damage is not so easy to deal with.

In places with good ventilation, gray mold can still be controlled. In places with poor ventilation, especially Kyoho grape lines with heavy dew at night, infection with gray mold or rachis blight can occur with a little carelessness, especially with Summer Black; if flower thinning, fruit setting, and enlargement treatments are not followed promptly with fungicides, they will all lead to large amounts of gray mold infection and berry drop.

Therefore, when growing grapes in the middle and lower reaches of the Yangtze River, from before flowering until after flowering, gray mold prevention must be done regularly and on schedule, while also controlling black pox and white rot. In other areas, as long as it is not a dry area, and as long as more dew can be seen on grape leaves in the vineyard in the morning, measures to control gray mold or rachis blight must be fully carried out.

Of course, vineyard owners who cannot see dew in the morning can easily avoid gray mold damage, but green plant bugs, aphids, thrips and other insect pests still need to be properly controlled. Gray mold damage occurs before flowering, at the young fruit stage, and at maturity. If it is not well controlled before flowering and at the young fruit stage, gray mold on fruit at maturity becomes uncontrollable.

The most effective means of dealing with gray mold is ventilation and humidity reduction, and the most effective chemicals are procymidone and boscalid. Pyrimethanil or iprodione are not the most effective, and too high a concentration of procymidone will burn leaves, so procymidone should be used carefully during the flowering period.

2. Harm of downy mildew

Downy mildew is the number one killer harming grapes, and it is also not very controllable. From the flower cluster extension stage all the way to leaf fall, it can harm the vineyard.

Downy mildew harms not only leaves, but also flower clusters and fruit. Moreover, many chemicals claimed to control downy mildew are not very effective against it.

Conditions for downy mildew germination: high temperature and rain are the primary conditions for downy mildew germination. If it is sunny and hot during the day and rains at night, then downy mildew is very likely to break out. A downy mildew outbreak cannot occur without a humid environment.

Therefore, in the dry areas of the northwest, there will be no gray mold or downy mildew damage throughout the year. In dry-hot valley areas such as Yunnan, in years with abundant rain, downy mildew and powdery mildew often break out together.

The most effective means against downy mildew is ventilation and humidity reduction, and the most effective chemical is dimethomorph, but dimethomorph cannot be used more than three times in a whole year, otherwise it will cause resistance. At other times, protective agents such as lime sulfur mixture, Bordeaux mixture, and mancozeb should be used well.

Too high a concentration of lime sulfur mixture will burn leaves, and Summer Black is very sensitive even to low concentrations of lime sulfur mixture, so it needs to be tested before use. Of course, if you are willing to spend money, azoxystrobin can also be used as a protective agent.

3. Harm of powdery mildew

This is the third major killer harming grapes. It infects leaves, covering the grape surface with a layer of white ash, and also infects fruit. Fruit harmed by powdery mildew may drop berries in severe cases, or crack in mild cases.

In the Yangtze River basin, powdery mildew generally causes damage after autumn, and a dry environmental climate is most suitable for the growth of this pathogen. Including the arid areas of the northwest, powdery mildew damage will break out.

In dry-hot valley areas with alternating humidity and dryness, powdery mildew and downy mildew cause damage at the same time. Vitis vinifera varieties are heavily infected, the Euro-American hybrid Golden Finger is especially susceptible to powdery mildew, and Shine Muscat is also not resistant to powdery mildew. Kyoho grape lines have better resistance to this variety.

The most effective chemicals against powdery mildew are kresoxim-methyl, cyproconazole, ethirimol, trifloxystrobin · tebuconazole and other chemicals. The cheapest chemicals are sulfur powder or sulfur suspension concentrate, and lime sulfur mixture and Bordeaux mixture are all very effective; the key is knowing how to use them.