A Detailed Guide to the Latest Control Methods for Cucumber Powdery Mildew

Cucumber powdery mildew is one of the common diseases in cucumber cultivation and occurs all over the country. Because powdery mildew has developed a certain degree of resistance to fungicides in recent years and can occur in all four seasons, control has become somewhat difficult. As a result, yields are generally reduced by about 10% in ordinary years, and by about 20 to 40% in epidemic years. Let us take a look below at how to control cucumber powdery mildew!

Symptoms of Cucumber Powdery Mildew

Cucumber powdery mildew damages leaves most severely, followed by leaf stalks and stems, and generally does not harm the fruit. In the early stage of the disease, small nearly circular white powdery spots appear on the upper or lower surface of the leaves and gradually expand into large white powdery areas with indistinct edges, covering the leaf surface as if a layer of white powder had been sprinkled on it. After wiping off the white powder, the leaf surface can be seen to have lost its green color, turning yellow, dry and brittle. When the disease is severe, the leaf surface is covered with white powder and turns grayish white until the entire leaf dies. After powdery mildew infects leaf stalks and tender stems, the symptoms are similar to those on the leaves, except that the lesions are smaller and the powdery material is also less. On the leaves, small yellow spots begin to appear and then expand into circular or oval lesions, with a white powdery mold layer on the surface.

Causes of Cucumber Powdery Mildew

1. High planting density and poor ventilation and light penetration lead to severe disease; applying too much nitrogen fertilizer makes the plants grow too tender, reducing resistance and making them susceptible to disease.

2. Heavy, acidic soil, many years of continuous cropping, large amounts of diseased residues in the field, insufficient fertility, rough cultivation, and fields overgrown with weeds reduce plant resistance and lead to severe disease.

3. Fertilizer that is not fully decomposed, organic fertilizer carrying pathogens, or fertilizer mixed with diseased residues of crops in the same family makes plants susceptible to disease.

4. Warm climate, dry air, constant alternation between drought and humidity, and insufficient light make plants susceptible to disease; long-term dryness after consecutive overcast and rainy days also makes plants susceptible to disease.

How to Control Cucumber Powdery Mildew?

1. Choose plots with good ventilation, loose and fertile soil, and convenient drainage and irrigation for planting. Properly apply phosphorus and potassium fertilizers in combination to prevent nutrient deficiency and premature aging, enhance plant disease resistance, do not water on cloudy days, and ventilate more on sunny days to reduce the relative humidity in the greenhouse or plastic tunnel and prevent excessively high temperatures, so as to avoid stuffy heat. In the early stage of cucumber powdery mildew or before the disease occurs, protective fungicides are mainly used to prevent infection and disease development.

2. When symptoms of powdery mildew damage appear on leaves in the field, attention should be paid to using fast-acting therapeutic agents and to adding an appropriate amount of protective fungicide for reasonable mixing, so as to prevent the disease from further worsening and spreading. Experience shows that when powdery mildew occurs, watering lightly between cucumber rows can increase air humidity and, combined with spraying, can control the disease at one stroke. Auxiliary measures also include avoiding excessive application of nitrogen fertilizer, increasing application of phosphorus and potassium fertilizers, and clearing diseased residues after vine removal.

3. Spray promptly in the early stage of the disease. For prevention, use 25% azoxystrobin suspension concentrate at 1500 times dilution, or 10% difenoconazole water-dispersible granules at 2000 times dilution. When scattered spots occur, immediately spray 32.5% difenoconazole · azoxystrobin suspension concentrate at 1500 times dilution, or 25% tebuconazole emulsion in water at 3000 times dilution, or 6% fenarimol wettable powder at 1500 times dilution, or 50% kresoxim-methyl water-dispersible granules at 3000 times dilution, or 12.5% diniconazole wettable powder at 2000 times dilution, or 33.5% quinolinone suspension concentrate at 800 times dilution. Or 8% flusilazole microemulsion at 1200 times dilution, or 30% nonylphenol copper microemulsion at 400 times dilution.