The symptoms of grape downy mildew

Grape downy mildew is almost distributed in every grape producing area in our country, and the damage is most serious in Shandong coastal area. Other producing areas mostly occur in regions and years with more rainwater. In the epidemic year, the diseased leaves were scorch and dried early, and the diseased leaves were distorted and stunted, which had a great impact on tree vigor and yield.

The main symptoms are as follows: grape downy mildew began to occur from May to June, and from August to September entered the onset of the disease. Diseases can 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 layer of white downy mildew is formed on the back of the lesion, which is the pathogenic sporangia and sporangia. The lesions eventually become brown and dry, and the diseased leaves also dry and fall early. 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. The disease occurs in most of our country's producing areas in the autumn, but in some rainy or rainy years, it can also be popular in the early stages of grape growth, which has a great impact on the yield.


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