The main symptoms are as follows: harm all young tissues of the aerial parts of the plant. After the leaves were invaded, they initially showed semi-transparent, oily spots with unclear edges, which in turn often combined with large lesions, mostly yellow to brown polygons. When the weather is wet or the humidity is too high, a white layer of downy mildew is formed on the back of the lesion. The lesions eventually become brown and dry, and the diseased leaves also dry and fall off. New shoots, tendrils, cobs, and petioles began as translucent, oily spots that developed into yellow-to-brown, pitted, indeterminate lesions, and lesions in the wet also produced a white layer of downy mildew. The growth of the disease has stagnated, distorted, and even died. After the young fruit is infected, the disease department fades, hardens and sinks, and a white layer of downy mildew grows, then the diseased fruit falls off; when the fruit is half large, it is infested, and the diseased fruit is brown soft and rot, soon shrinks and falls, the fruit coloring. After the germs no longer infested. Diseased fruits have reduced sugar content and deteriorated quality.
Second, the incidence conditions
1. Climatic conditions: The severity of the disease has a close relationship with climate conditions. In general, the cold and humid climate is conducive to disease. In the spring and fall seasons, the occurrence of grape downy mildew is less severe in areas with less wind, fog, more dew, and more rain.
2. Orchard conditions: The orchard is cold and humid, the plants and leaves are too dense, the scaffolding is too low, and when the ventilation and light transmission are poor, the incidence is heavier.
3. Varieties: In cultivars, grapes in the American system are generally more disease-resistant and grapes in the European system are more susceptible to disease. There are many reasons for the differences in disease resistance among grape varieties, and there are morphological and other factors.
Third, prevention and treatment methods. Mainly from the combination of cultivation and management and chemistry to prevent and control work.
1. Clear Garden in Winter: Clean the fallen leaves, cut away the diseased branches, and carry out deep soil turning in order to eliminate or reduce the source of overwintering diseases.
2. Water and Fertilizer Management: Adjust the orchard's microclimate, strengthen the orchard's ventilation and light transmission, and reduce the humidity in the orchard; specific measures include: appropriately widening the row spacing, paralleling the direction of the main wind direction of the local area, and keeping the shelving not too low; avoid partial nitrogenous fertilizer and increase the application of phosphate fertilizer. Potassium fertilizer and lime to improve the plant's resistance to disease; During the growth of the plant, should be timely and appropriate amount of water, after the rain pay attention to the park drainage; reasonable pruning, as far as possible cut off the unnecessary branches near the ground, in order to reduce the humidity on the ground, reduce the invasion of pathogens Dyeing opportunities.
3, spray protection: to capture the key period before the bacteria infection, spraying the first drug, sprayed once every other half, continuous spray 2-3 times. The agents that can be used are: Bordeaux mixture 1:0.7:200. The drug has specific effects on grape downy mildew; 65% Zexone zinc WP 500 times, this agent has a good control effect. In recent years, the newly produced 40% EB aluminum wettable powder 300 times, has special effects on the prevention and treatment of the disease.
In addition, some new types of bactericides are now being produced, such as anti-virus (dark zinc manganese), DPx-3217, etc., such as the use of 1000-1200 times the antivirus, in the peak period of grapevine downy mildew, plus spray 1-2 Second, its control effect is better than Bordeaux's solution. It is also effective to control grape downy mildew by spraying it with 800 times liquid of thimemus (35% wettable powder).
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