The Incidence and Control Measures of Rose Black Spot
July 22 11:22:55, 2025
Rose black spot is a widespread and serious fungal disease that affects roses across the globe, particularly in regions where roses are cultivated. In recent years, this disease has become increasingly prevalent in many provinces across China, causing significant damage to rose crops. The occurrence of black spot can lead to premature leaf drop, which not only hinders the growth of the plant but also reduces the survival rate of cuttings. As a result, the ornamental and economic value of roses is greatly diminished. Moreover, the disease can affect not only roses but also other species within the rose family.
Symptoms of the disease typically appear on the leaves, although they can also develop on the petioles and stems. On the leaves, the lesions are usually round or nearly round, dark brown in color, and often have a radial pattern around the edges. Lesions on the petioles and stems, however, tend to be elongated and lack distinct radial boundaries.
The disease cycle begins in mid-May in Beijing, with a severe outbreak occurring during the rainy season in July and August. By October, the disease activity tends to decrease, and by early November, it stops altogether. In southern China, the disease usually starts in April, peaks during the rainy months of June and July, and gradually declines by August. It may reappear in September and October before ceasing again in November. Wet and rainy conditions significantly favor the development and spread of the disease. Early and heavy rainfall can cause the disease to appear earlier, spread more rapidly, and cause greater damage. Poor ventilation in greenhouses, high humidity, and dense planting of cuttings all contribute to the favorable conditions for the disease to thrive.
To manage black spot effectively, several control measures can be implemented. First, reducing the source of infection is crucial. In autumn, all fallen leaves and debris should be removed, and infected shoots should be pruned during winter. A 1% copper sulfate solution can be applied during dormancy to kill overwintering pathogens.
Second, improving cultivation practices plays a key role. Planting disease-resistant varieties and spacing them appropriately can help prevent the spread of the disease. When watering, avoid overhead irrigation and instead use root watering to minimize spore splash. Greenhouses should ensure good air circulation and maintain lower humidity levels. Proper care and management can enhance the plant's natural resistance to disease.
Third, chemical treatments are an essential part of the control strategy. Fungicides such as 80% dexamethasone wettable powder (diluted 500 times), 70% thiophanate-methyl wettable powder (diluted 1000 times), 50% carbendazim wettable powder (500–1000 times), or 75% bacterial liquid wettable powder (1000 times) can be effective. A small amount of Bordeaux mixture can also be used, though caution is needed due to roses' sensitivity to lime. Other options include benzene-based fungicides, captan, and mancozeb. Spraying should be done every 7–10 days, and different fungicides should be rotated to prevent resistance.
Finally, selecting disease-resistant varieties and rootstocks is an important long-term strategy. Replacing susceptible varieties with resistant ones helps reduce the risk of infection and improves overall crop health. By combining these methods, growers can effectively manage black spot and protect their rose plants from damage.