Why does grape downy mildew occur? What are the prevention and control techniques?

Grape downy mildew is a specific parasitic disease, which is one of the important diseases harmful to grape production. It is distributed in the main grape producing areas in the world. So why does grape downy mildew occur? What are the prevention and control techniques?

First, why does grape downy mildew occur?

As long as it is a grape grower, we must know that downy mildew likes to spread in a low temperature and high humidity environment, which begins to occur from May to June, and the peak period is from July to September. But we need to explain it a little bit more:

1. Temperature

When the temperature reached 11 ℃, the oospore could germinate in water or moist soil, the sporangia could be formed at 5-27 ℃, and could germinate at 12-30 ℃. Low temperature at night was also beneficial to sporangium germination and invasion. These are the basis of bacterial infection.

2. Humidity

Humidity and Rain Water are two major limiting factors. The germination and invasion of sporangia and zoospores require rain and dew. 95% to 100% humidity is the best.

3. Rainfall

The prevalence of the disease is also related to the distribution of seasonal rainfall. For example, if the rainfall is abundant and frequent from May to September, the disease is more serious. If the summer temperature is 22 ~ 27 °C, it is cloudy and rainy for 10 consecutive days, or if there is a rainstorm every 8 to 15 days, and the air humidity reaches more than 95%, there will also be a peak of incidence.

4. Fertilization

Improper fertilization, partial or late application of nitrogen fertilizer will stimulate the emergence of new grapes, the disease is serious, the proportion of potassium in grape cell fluid is one of the important factors to determine disease resistance, grapes with more calcium have stronger resistance to downy mildew.

5. Management ability

Grape cultivation density, scaffolding orientation, pruning and pruning are closely related to the occurrence of downy mildew.

Second, what are the prevention and control techniques of grape downy mildew?

1. Clear the garden thoroughly

Downy mildew pathogen overwinters with diseased branches, diseased fruits and diseased leaves falling to the ground. Clearing the garden is an effective measure to eliminate the source of overwintering bacteria.

2. Cultivate a strong tree

Reasonable water and fertilizer, strengthen management, promote the tree growth strong but not prosperous, really achieve the moderate tree potential, and strive to improve the disease resistance ability of the tree.

Critical period of water demand: before sprouting, before and after flowering, color changing period, mature period, burying soil to prevent cold.

The critical period of fertilizer requirement: germination period, fruit expansion stage, color conversion period, after harvest and before overwintering. Pay attention to the application of organic fertilizer, fertilize according to the demand of grape for nutrient elements, cooperate with sea elves biological stimulant to achieve balanced nutrition, promote root growth, improve soil environment, stimulate plant wildness and other multiple effects.

Strengthen management: do a good job in orchard drainage, reasonably control the amount of auxiliary shoots in summer, cut off unnecessary vine leaves close to the ground, pay attention to timely shoot thinning and vine binding, and reduce the initial infection of bacteria from aboveground leaves. Diseased leaves and fruits were found to be removed in time, buried deeply and disinfected.

3. Chemical control

At present, the agents for the prevention and control of downy mildew are the most used in grapes, and a clear distinction should be made between protective agents and therapeutic agents.

Protective agent: use the medicine before the disease of the crop to prevent the infection of germs. When downy mildew has occurred, the mildew layer has been formed to reuse the protective agent, the effect is definitely not good.

Therapeutic agents: after the onset of the disease, drugs are used to cut off the spread of pathogenic bacteria and control the further development of the disease. Therefore, the use of protective agents before the onset of the disease and therapeutic agents after the onset of the disease is the basic principle of our drug selection.