Grapes are afraid that no one does not know the downy mildew, it is harmful, rapid, and difficult to control. In the case of a suitable climate, and not to mention the rain, the dew is slightly larger, and it is very likely to erupt. The degree of terror is evident.
In recent years, the resistance of downy mildew has risen rapidly, and the harm has increased year by year. The way of infecting is even more innovative, which is really a headache!
Downy mildew
The pathogen of downy mildew is unicorn mold, belonging to the genus Flagellate, Oomycetes, Downy Mildew, and Monochobacter, which are obligate parasites. The mycelium spreads between the host cells, and the tumor-like aspirator extends into the host cell to absorb nutrients.
Downy mildew
Downy mildew is the most common form of damage on the leaves, so don't think it only harms the leaves. Such as young shoots, tendrils, petioles, inflorescences, cobs, fruit, etc., but all the green and young tissues are deeply affected!
Leaf damage
After the leaves are invaded, the oily small spots with translucent and unclear edges are initially formed, and then often combined with each other to form large lesions, mostly yellow to brown polygons.
When the weather is wet or the humidity is too high, a white frosty layer is formed on the back of the lesion. In the later stage, the lesions are dry and brown, and the diseased leaves are easy to fall off early.
Young shoots suffer
After the young shoots are damaged, water-spotted spots form, and then become brown-stained lesions. When wet, the lesions also produce white downy mildew.
When the disease is heavy, the new shoots are twisted, the growth stops, and even die. The tendrils, cobs, and petioles can sometimes be killed, and their symptoms are similar to those of young shoots.
Inflorescence victimization
After the flower bud is damaged, it becomes dark brown, and the surface is covered with white mildew, and the wilting falls off.
Young fruit victim
After the young fruit is infected, the diseased part fades, hardens and sinks, and a white frosty layer grows, and the diseased fruit falls off.
Victimization of fruit enlargement
When the fruit is swollen, it is damaged, it is brown and soft, and it will shrink and fall off soon. After the fruit is colored, it will not be infected.
Recently, grapes in many areas have experienced different degrees of "black particles", partly due to infection with downy mildew.
The fruit of the downy mildew is characterized by the fact that the junction of the stalk and the fruit is the first to occur, and then the fruit becomes brown and sag, and the phenomenon of granules is more serious.
In addition, physiological reasons also account for a part. Such as airburn, boron deficiency, improper fertilizer and water, etc. will also cause the surface of the fruit and the flesh to become black.
The worse one is a comprehensive disease caused by the mixing of physiological diseases and downy mildew. This is not the case.
In either case, attention should be paid to improving the tree, strengthening field management, removing diseased grains in a timely manner, and preventing and controlling diseases such as downy mildew, white rot, and gray mold.
Prevention and treatment of downy mildew
Judging from the incidence of downy mildew in recent years, there are two characteristics, one is getting earlier and earlier, the second is getting more and more heavy! The weather factor is certainly there, but the improper management measures are the main cause.
Therefore, for the prevention and control of grape downy mildew, it is necessary to take the tree as the purpose, and preventively the main preventive measures.
Thoroughly clearing the garden
Downy mildew is the winter when the diseased branches, diseased fruits and diseased leaves fall into the soil. It is a powerful measure to eliminate the source of wintering bacteria.
Cultivate robust trees
Reasonable water and fertilizer, strengthen management, promote the growth of the tree body, but not prosperous, truly reach the golden mean, and strive to improve the disease resistance of the tree.
Key period of water demand : before germination, before and after flowering, during color change, at maturity, and when burying soil for cold protection.
Key period of fertilizer requirement: germination stage, fruit expansion period, color change period, post-harvesting and wintering. Pay attention to the application of organic fertilizer, according to the grape's demand for nutrients, and with the sea snail bio-stimulant, to achieve balanced nutrition, promote root growth, improve soil environment, stimulate plant wildness and other multiple effects.
Strengthen management: do a good job of water drainage in the orchard, control the side shoots in a reasonable leaf curtain in summer, cut off unnecessary vine leaves close to the ground, pay attention to timely tying the vines, and reduce the initial infection of the bacteria from the upper leaves. The diseased leaves and diseased fruits were found to be removed in time, concentrated and buried.
Chemical control
â— In the rainy season, it is necessary to carry out standard prevention and control for downy mildew disease, that is, use a disinfectant once every 10 days, generally with protective fungicides.
Common protective fungicides include copper preparations (bordeaux solution, copper quinoline, copper rosinate), mancozeb, captan, tebuconazole, cyanoxazole, pyraclostrobin and the like.
Copper preparation, mancozeb: It is not safe to use before bagging, and it is easy to cause phytotoxicity.
Captan and tebuconazole: white rot and mildew are effective, have a good effect, and do not damage fruit powder.
Cyansulfazole: high activity, long-lasting effect, and no obvious resistance. The defect is that the sterilization spectrum is narrow and the conductivity is general.
Pyraclostrobin: only for preventive use. Cannot be mixed with silicone or emulsifiable products.
Pay attention to the use in advance, evenly and thoughtfully when spraying, especially the back of the leaf.
â— In the early stage of the disease, the main focus of the disease center is prevention and treatment, with therapeutic agents as the mainstay.
Common therapeutic fungicides include metalaxyl, cymoxanil, propofol, enoylmorpholine, fluthiazolone, carbazolam, fluopyram, chlorobromoisocyanuric acid, and the like.
Metalaxyl, cymoxanil: quick effect, safe to use, but short duration, it is recommended to mix with protective agent.
Creamy mildew: good systemic, safe, bactericidal activity, high concentration can be used to achieve control effect.
Dimethomorph: The resistance is obvious, and the concentration should be increased to ensure the control effect.
Fluorothiazolpyridone: quick-acting type, long-term effect is very good, but the point of action is single, the effect of resistant downy mildew is not obvious, it is recommended to prevent.
Flupiramide: Absorbent block, resistant to rain, suitable for rainy seasons.
Oxazone: kills resistant mutant mildew and has a long-lasting effect.
Chlorobromoisocyanuric acid: high-efficiency broad-spectrum, but short-lasting effect. It is recommended to use the disease during the outbreak and mix it with other protective agents.
Spraying can first use the contact fungicide to remove the mildew on the back of the diseased leaf, then spray the therapeutic fungicide, and finally use a protective fungicide to consolidate the effect.
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