Look at the grape “Golden fingers”. They are nearly matured, but now already lost the commodity value due to its bad appearance. The fruits are from big young fruit stage to stone hardening stage, the upper part to the fruit stalk turns black. For the severe fruits, the surface become drying and shrinking. Cut the fruits and you will find the flesh turns black r brown from the fruit stalk.
In the grape plantation, there are 3 kinds of diseases that have near symptom:
Scorching, Boron deficiency, Downy mildew
From the pictures, we can see the difference:
1: If it’s Scorching and Boron deficiency, the fruits stalk and the ear axis will not change the color; But if it’s downy mildew, the fruits’ stalk and ear axis will turn to dark-brown and watery.
2: The Scorching disease farms the grape from the outside to inside and mainly shows as spots, but Downy mildew is from the inside to outside and shows as wide range problems.
3: Boron deficiency starts around the seeds and the total fruits turn black. The skin will not be sunken, or a little sunken.
4: If it’s Scorching or Boron deficiency, the fruits will not drop. But if it’s Downy mildew, the fruits will drop and will drop faster after treatment.
To confirm the exact disease, we can do the cultivation with moisture retention.The method is: Split the fruits, put them into a moisture plastic bag packed with towel, then put them under a place with temperature around 23-25°C for 24 hours with light blocking. If there are Downy mildew’s hypha in 24 hours, keep the same condition till 48 hours. If still no hypha then, should consider other reasons. But there’s exception, for example, if just applied fungicides or if the cultivation condition doesn’t reach the standard, we cann’t find the hypha finally.
After confirming the disease, we should take different actions. Here we would like to give some suggestions for the control of the Downy mildew:
1: In the past, Downy mildew will not harm the fruits. This case is becoming heavier and heavier in the latest years. We think it has connections with the predatory cultivation, fungicides’ abusing and few focus onto the grape tree’s protection. The grape tree itself has resistance to the diseases. But the continuous high-yields let the trees in the fatigue state indeed. That’s why kinds of phisiological diseases occur very often and some nameless diseases start to harm too. The abusing of the inferior fertilizer and hormone’s abusing.
2: The climate’s changing, environment’s destroying intensify the diseases’developing. For example, in many places, the diseases that usually occur from June to August, but now maybe occur in advance to April. For example, Downy mildew is more likely to occur at the temperature 23-25°C and will be inhibited over 30°C. But from July 11-August 02, 2016, in Hefei province, the night temperature was over 30°C, but the Downy mildew still occurred in wide range and was difficult to control.Even we control the usage of the hormone and chemical fertilizer, but we cann’t be sure whether other materials contain them or not?
3: Since we cann’t control the nature and change them, we should do our best using our best familiar methods. The best way is still combining the prevention with cure. Followings are some recipes that we used to control the grape’s Downy mildew: Bordeaux mixture 80% WP+Dimethomorph, Bordeaux mixture 80% WP+Fosel-aluminium, Bordeaux mixture 80% WP+Cymoxanil. They have low cost and good protective effect. We still can use other copper fungicides like Oxine-copper, Copper hydroxide. We still can use Mancozeb+Dimethomorph, Cymoxanil+Zineb, Cymonixal+Propineb, etc.. There are still many recipes that work. But we would like to strengthen some points that: At initial occurring stage, can apply some amino acids fertilizer because they can fasten the spots’ repairing, Calcium fertilizer can increase the leaves’ resistance to the fungi, use fungicides with insecticides.