How to treat rose black spot
In midsummer, the black spots quietly appearing on the leaves of the rose make countless gardeners worried. This black spot disease, known as "rose cancer," not only affects ornamental value, but also causes large-scale leaf fall and causes plant death. Only by mastering scientific prevention and control methods can you keep your roses away from disease threats. Analysis of the pathogenesis of rose black spot disease: characteristics and transmission mode of pathogenic fungi lurking through the winter in the form of conidia, and its unique two-celled structure (large upper part and small part) has strong environmental adaptability. Spores spread by splashing rainwater can complete the infection process after the leaves are wetted for 6 hours. The high humidity season from May to September every year is a high-risk period for disease outbreaks. The typical symptom identification guidelines initially present small purple-brown spots and expand into a 3-mm black round spot within 3 days. The characteristic yellow halo is the key to diagnosis. The "green island phenomenon" appears in the middle and late stages-that is, green patches remain on yellowed leaves, and the plants have lost 80% of their photosynthetic capacity. Only new top leaves are left in severely affected plants, which seriously affects flower bud differentiation. Analysis of environmental influencing factors The disease spreads fastest when relative humidity is>85%, and temperature is 22-28℃. Closely planted potted plants (spacing <30cm) triple the incidence, and the risk of infection increased by 60% when watering plants in the evening. Experiments have shown that gardens using sprinkler irrigation systems have a 47% higher infection rate than drip irrigation systems. Systematic control plan for rose black spot disease Four-step physical control ① Garden clearing in winter: Completely remove the sick body, spray 3°Be stone sulfur mixture after pruning to seal the garden ② Build a rainproof canopy: Reduce the water contact time of the leaves to less than 2 hours ③ Improve watering: Use siphon drip irrigation, and control the watering time between 9:00 a.m. ④ Enhance resistance: Apply seaweed fertilizer + potassium fulvate every month to increase the thickness of the leaf cuticle. Chemical control golden ratio prevention period (March-April): Mancozeb 800 times solution + brassinolide, spray every 15 days at the beginning of the disease: 2000 times solution of difenoconazole +1500 times solution of azoxystrobin, focus on spraying on the back of the leaves for severe treatment: 4000 times solution of flusilazole and pyraclostrobin are used alternately, combined with penetrating agent silicone. Through actual measurement, using this control system can reduce the rate of diseased leaves by 92%, and prolong the flowering period by 20 days. It is recommended to cooperate with the use of EM bacteria for biological control to establish a stable microecological protection barrier.