The Control Methods of Rose Blight and Downy Mildew
An introduction to the related information of rose, rose blight and downy mildew prevention methods, details are as follows:
Symptoms
The leaves, new shoots, and flowers of roses can all be affected. Initially, irregular light green spots appear on the leaves, which then expand to become brown and dark purple, and finally grayish-brown. The edges are darker, gradually expanding and spreading to healthy tissue without a clear boundary. In humid weather, a sparse grayish-white downy mildew layer can be seen on the back of the diseased leaves. Some lesions are purple-red with a gray-white center, similar to being burnt by fertilizer or pesticide. When new shoots and flowers are infected, the lesions are similar, but those on the shoots are slightly sunken. In severe cases, the leaves wither and fall off, and the new shoots rot and die.
Causal Agent
The causal agent is Perenospora sparsa Berk, belonging to the Oomycetes class and Peronosporales order. The sporangiophores are 350 micrometers long, with sharp-angled branched forks, and the apex is slightly curved and pointed. The sporangia are sub-ellipsoid to spheroid, measuring 17-22 by 14-18 micrometers. The sporangia can germinate in water at 18°C within 4 hours, will not germinate below 4°C or above 27°C. Oospores are rare.
Infection Pathway
In the presence of oospores, the downy mildew pathogen overwinters, but the mycelium within the stem can survive for many years, overwintering and surviving the summer, producing sporangia from which sporangia are formed to spread infection. The disease mainly occurs in greenhouses, with the end of March to mid-April and mid-November being more severe, with 90-100% humidity and relatively low temperatures conducive to disease development. The disease occurs frequently in densely planted rose seedlings in greenhouse beds. Poor ventilation, overly wet soil, and excessive nitrogen fertilizer can aggravate the disease.
Control Methods:
1. Remove infected leaves, stems, and flowers to reduce the source of infection.
2. Improve ventilation and reduce humidity in greenhouses to reduce the incidence of the disease.
3. Spray 58% metalaxyl-manganese zinc 500 times liquid, or a mixture of 25% metalaxyl (methylaxyl) and 65% mancozeb in a 1:2 ratio diluted 500 times, or 40% phosphonate (疫霉灵) 200-250 times liquid, or 75% bavistin wettable powder 600 times liquid, or 70% tanosine-copper 250 times liquid, or 40% enhanced metalaxyl 500 times liquid, or 60% DTM (dimethomorph + phosphonate) wettable powder 500 times liquid, or 50% cuprous oleate wettable powder 500 times liquid, etc., every 6 days for 3-4 times. Alternate the use of different fungicides and ensure uniform and thorough spraying.
The above is a specific introduction to the prevention and control methods of rose blight and downy mildew for reference by netizens.