A Detailed Guide to the Latest Control Methods for Rose Leaf Blight
Leaf blight is one of the common diseases of roses. An infected rose first develops lesions from the tip or edge of the leaf. As the disease progresses, the lesions grow from small to large in an irregular shape, and the color changes from reddish-brown to grayish-brown. Finally, the lesions merge into large dead patches. If the disease is severe, it can cause the death of the rose plant. Now let us take a look at the control methods for rose leaf blight!
Symptoms of Damage
Rose leaf blight often causes the leaves of nursery and potted roses to dry up and drop off. The pathogen mostly invades from the leaf tip or leaf margin, initially appearing as small yellow spots, which then rapidly expand inward into large irregular patches. On severely affected leaves, up to 2/3 of the entire leaf dries up. The diseased area loses its green color and turns yellow, then brown, dries up and drops off, and sometimes sparse small black dots appear on the leaf surface.
Occurrence Pattern
The leaf blight pathogen belongs to the Coelomycetes, order Sphaeropsidales. The small black dots on the leaf surface are the pathogen's pycnidia. The pycnidia are spherical or nearly spherical, light brown, with an ostiole at the top. They are initially embedded in the leaf tissue and later break through the epidermis to become exposed, producing many conidia inside to carry out infection and cause damage. The disease is most severe during the high temperature and high humidity period from July to September.
Control Methods
1. Agricultural control: Remove diseased leaves both above ground and below ground to eliminate the overwintering pathogen. If diseased leaves are promptly picked off during the disease period, the spread of the disease can be effectively controlled.
2. Chemical control: During the disease period, spray with 75% chlorothalonil at 600-800 times dilution or 25% carbendazim at 500 times dilution.