What is the best fungicide to control rose black spot?

Rose black spot disease is also called brown spot disease. It is a worldwide rose disease. You should first start from the source of infection, and it is best to begin spraying the fungicide when new leaves unfurl in summer. So what fungicide should be used for rose black spot?

1. What fungicide should be used for rose black spot?

1. First, start from the source of infection, promptly sweep up fallen leaves and remove diseased leaves. In winter, pruning of severely affected plants should be strengthened, and the overwintering pathogens on diseased branches and leaves should be removed as well.

2. Do not arrange potted plants too densely. Placing them directly on the ground can easily make the potting soil too wet because of standing water on the ground, so it is best to place them on stepped plant stands. Change the watering method and timing: water slowly along the edge of the pot rather than spraying frequently. Never water at night, because moist leaves make it easier for pathogens to invade.

3. When using chemical treatment, start spraying when new leaves first emerge in summer, usually once every 7-10 days. The fungicide can be chlorothalonil wettable powder at 500 times dilution (75%), or carbendazim wettable powder at 500-1000 times dilution (50%), or zineb wettable powder at 500 times dilution (80%), or Bordeaux mixture (1:1:100), or thiophanate-methyl at 1000-1200 times dilution (70%).

2. Symptoms of rose black spot

The young shoots, flower stalks and leaves of roses can all be infected. Small purplish-brown or brown spots are the initial form of the lesions, which then expand into dark brown or black round spots about 1.5-3 mm (in diameter); some have fringed edges, while some cultivars have smooth, neat edges.

The lesions are often surrounded by yellow halos. The lesions usually join together in groups, and the diseased leaves turn yellow over large areas, making the lesions look like “small islands” with green edges.

Diseased leaves fall off easily, though a few rose cultivars do not drop their leaves. Young branches and flower stalks develop purple or black streak-like spots and are slightly sunken. When the disease is severe, all the leaves on the middle and lower parts of the whole plant fall off, leaving only a few new leaves at the top.

Although rose black spot is very serious, as long as prevention and control work is done well, the impact is still relatively small. Friends who grow roses must take good care to avoid black spot infection.