Control Methods for Black Spot Disease in Roses
Today's focus is to introduce the experience of the floral clinic in the aspect of roses, specifically the prevention and treatment methods for black spot disease in roses, as detailed below:
Black spot disease in roses, also known as brown spot disease, is a worldwide rose disease.
Symptoms
Rose leaves, young branches, and flower pedicels can all be affected. Initially, the spots on the leaves are purplish-brown to brown dots, which then expand into round spots 1.5 to 13 millimeters in diameter, black or dark brown, with a fringed edge, but the edges of some varieties can also be smooth. There is often a yellow halo surrounding the spots. Under a magnifying glass, black pustular-like granules can be seen on the affected area. The spots often connect with each other, causing the surrounding leaves to turn yellow, making the spots look like "islands" with green edges. Diseased leaves are prone to falling, but some rose varieties do not shed. Young branches and flower pedicels develop purple to black streak-like spots that are slightly sunken.
When the disease is severe, the entire lower and middle parts of the plant shed leaves, leaving only a few new leaves at the top.
Causal Agent
It is a fungus of the genus Actinonema, Actinonema rose (Lib.) Fr. The conidiomata are located under the host's cuticle and later protrude through the epidermis. They are 108 to 198 micrometers in size, with short and inconspicuous conidiophores. The conidia are elliptical or fish bladder-shaped, 18 to 25 X 5 to 6 micrometers in size, bicellular, with the upper smaller and the lower larger, slightly constricted at the partition. The apex is beak-like and often biased to one side.
Transmission Pathway
The mycelium overwinters on diseased branches, leaves, or fallen leaves, and in early spring of the following year, it forms conidiomata, producing conidia that spread the disease. The conidia are also one of the initial sources of infection. Conidia are transmitted by wind, rain, and splashing water droplets, so the disease is more likely to occur in rainy, foggy, or dewy conditions. According to experiments, when there is stagnant water on the leaves, the spores can germinate and infect within 6 hours.
The optimal temperature for germination and invasion is 20 to 25°C, with a pH of 7 to 8. The latent period is 10 to 11 days, slightly longer for older leaves, at 13 days. The pathogen can repeatedly infect, and the disease can occur throughout the growing season. The disease is severe during the plum rain season and typhoon season, and it spreads slowly during the hot summer and dry season. Weak plants are more susceptible to the disease. There is variation in resistance among varieties, but no immune varieties.
Control Methods
1. Regularly sweep away fallen leaves and remove diseased leaves to reduce the source of infection. In winter, severely prune heavily infected plants and remove the overwintering pathogens on the diseased stems.
2. When potting, avoid placing the plants too closely together, and do not place them directly on the ground to prevent the soil from becoming too wet when water accumulates on the ground. It's best to place them on stepped plant stands. Improve the method and time of watering; water should be poured from the edge of the pot to avoid spraying. Do not water in the evening to prevent leaves from remaining wet and being prone to pathogen invasion.
3. Chemical control. When new leaves just unfold in summer, start spraying with a fungicide every 7 to 10 days. The fungicides used include 50% carbendazim wettable powder at 500 to 1000 times dilution, or 75% chlorothalonil wettable powder at 500 times dilution, or 80% mancozeb wettable powder at 500 times dilution, or a 1:1:100 Bordeaux mixture, or 70% metalaxyl at 1000 to 1200 times dilution.
After pruning in winter, a Bordeaux mixture of 3 to 5 degrees can also be sprayed to eradicate the pathogen.
The above is a detailed introduction to the prevention and treatment methods for black spot disease in roses, have you understood it?