How to achieve good control of powdery mildew on cut roses

Powdery mildew is the most common disease of rose leaves. Prevention should be the main approach, combined with control, to achieve substantial results.

Prevention methods include:

1. Before the plants break dormancy in early spring, spray once with carbendazim wettable powder at 600 times dilution to kill overwintering pathogens.

2. After the rose plants leaf out the following spring, spray carbendazim wettable powder at 1000 times dilution once every half month, for 3 to 4 consecutive times, to consolidate the preventive effect; or use equal-amount Bordeaux mixture sprayed once every half month after leafing out, for 3 to 4 consecutive times, which can form a good protective film on the rose leaves and prevent the invasion of pathogen spores.

3. Use 50 to 100 g of 27% high-fat film emulsion, add 7 L of water before or during the onset of disease, and spray evenly on both the front and back sides of the leaves, once every week, for 2 to 3 consecutive times. This can form a light-transmitting, breathable protective film that not only prevents the invasion of pathogen spores but also does not affect the photosynthesis and respiration of the leaves. In addition, for cut roses grown in greenhouses, ventilation and air permeability should also be increased, and sufficient light should be provided to increase plant resistance, which can significantly reduce the occurrence of powdery mildew; likewise, avoid excessive nitrogen fertilizer, appropriately increase phosphorus and potassium fertilizer, and prune and burn infected branches and leaves in early spring, which is also very important.

Treatment methods:

1. During the disease-free period, use 15 to 20 g of 40% sulfur-carbendazim suspension concentrate (a broad-spectrum fungicide made by mixing carbendazim and sulfur), add 7.5 to 10 L of water, and spray on the leaf surface, applying once every 7 to 10 days, for 2 to 3 consecutive times. The effect is quite good.

2. Use triflumizole for control. Spray the first application at the early stage of disease, and spray the second application 10 days later. Generally use 30% triflumizole at 800 to 1000 times dilution; note that after application, immediately wash exposed areas such as the face, hands, and feet, and rinse the mouth. Do not pour the remaining pesticide into paddy fields, rivers, or fish ponds, so as to avoid harm to humans, livestock, and others; it is the preferred pesticide for treating powdery mildew.

3. During the growing season, choose 50% thiophanate-methyl at 1500 times dilution, 20% dinocap emulsifiable concentrate at 3000 times dilution, or 50% benomyl wettable powder at 1000 times dilution. Choose any one and spray the plants once a week, for 2 to 3 consecutive times, which also has a good control effect.