Rose black spot disease symptoms and transmission routes, prevent and control from the source to make flowers more robust

Rose black spot disease, also known as brown spot disease, is a relatively common disease of roses. First, you should start from the source of infection, promptly clean up fallen leaves and remove insect-damaged branches and diseased leaves. Use broad-spectrum fungicides for prevention and control starting from the early stage of the disease.

Beautiful roses

Symptoms of black spot disease

When roses are infected with black spot disease, mainly the young branches, pedicels and leaves of the rose can all be infected. Purple-brown or brown spots are the initial form of the lesions, and as time goes on the diameter of the lesions expands, with some edges appearing fibrous and hairy.

Rose branches and trunks attacked by the disease

The lesions are often surrounded by a yellow halo, and the lesions usually link together several at a time, causing large areas of the diseased leaves to turn yellow. Diseased leaves easily fall off, but there are also a few rose varieties whose leaves do not fall off. Young branches and pedicels develop black streak spots, slightly sunken. In severe cases, it will cause all the leaves on the middle and lower parts of the entire plant to drop off completely, leaving only a few new leaves at the top.

Rose black spot disease

Transmission routes of black spot disease

The main source of infection of black spot disease is the mycelium that remains over winter on diseased branches and diseased leaves, which forms conidia in early spring of the following year and is one of the initial sources of infection. Wind and rain and splashing rainwater are the transmission media for the conidia, so the disease is prone to occur in rainy weather, and in foggy or dewy weather. The pathogen can carry out multiple infections, threatening the entire growing period of the rose. It is especially most severe during the plum rain season and typhoon season, while high-temperature summer weather slows the spread of the pathogen. When the plant is weakened, the pathogen is more likely to infect it. Different varieties have different disease resistance, but none are immune to this disease.

Rose black spot disease

Control methods for black spot disease

1. First, you should start from the source of infection, promptly sweep up fallen leaves and remove diseased branches and diseased leaves. In winter, pruning work should be strengthened for severely diseased plants, removing the overwintering pathogens on diseased branches and diseased leaves one by one.

Rose black spot disease

2. Potted roses should not be placed too densely. Potted roses placed directly on the ground are very likely to have overly wet potting soil due to water accumulation on the ground. It is best to place them on a flower rack or lay a layer of bricks at the bottom to separate water. When watering, pour slowly along the edge of the flower pot and do not spray-water too frequently. Never water at night, because damp leaves make it easier for the pathogen to infect.

Roses grown on a flower rack

3. Use broad-spectrum fungicides and start spraying the pesticide when new leaves first unfold in summer, usually spraying once every 7-10 days. For the pesticide, you can choose chlorothalonil wettable powder diluted at 1:500, or 75% carbendazim soluble powder diluted at 1:800, or 70% thiophanate-methyl diluted at 1:1000 for preventive treatment.

Only careful care can make roses more robust