Recently, many gardeners have noticed numerous spots on the leaves of their roses. They have neither fertilized nor sprayed them, but have no idea what is causing this. You might think it’s black spot, but in reality, it’s probably downy mildew – a common rose disease in early spring.
Understanding the Symptoms and Characteristics of Downy Mildew
Downy mildew, like powdery mildew, tends to occur in high humidity environments. Roses are especially susceptible to downy mildew when temperatures are low and humidity is high. Infected areas usually develop a smear-like scar or look like they have been scalded with hot water.
If downy mildew infects a rose’s new shoots, it can cause them to wilt. As a result, in the early spring stage, many novice gardeners often find that new shoots of roses suddenly wilt after a rain, which is caused by downy mildew or early blight.
In addition, downy mildew is not only prone to appear in early spring, but also in the fall and winter seasons. During this time, downy mildew is more likely to infect the stems under the rose buds, causing them to wilt. When this damage occurs, it is often difficult for many gardeners to find the real cause.
For novices, experience is important, but systematic learning is even more critical. A comprehensive knowledge of planting will enable you to cope with problems when they arise. If you want to know more about rose care tips, we recommend you to read a very practical book – “How to raise roses from scratch”.
How to prevent and control downy mildew
Prevention
The prevention of downy mildew should start in the early spring when roses are germinating, especially those potted roses that have not been cleared during the winter and need to be treated in advance when it is rainy in the spring.
Commonly used preventive agents include carbendazim, chlorothalonil and metribuzin. These agents can effectively prevent downy mildew. However, it should be noted that drug prevention is only one of the means, and can not completely eliminate the occurrence of the disease. More important is to improve the maintenance environment.
For example, in the early spring stage, before the germination of roses can be sprayed in a timely manner to comprehensively sterilize and kill insects. After germination, too dense buds should be removed in time to maintain good ventilation inside the plant. At the same time, ensure that the maintenance environment is well ventilated.
Timely treatment
Once roses are infected with downy mildew, you should take measures as soon as possible. First, remove the infected leaves, and then spray a full range of fungicides. You can choose the above mentioned fungicides, or you can also use the fungicide for spraying. Fungicide has good systemic protection.
If downy mildew is more serious, it can be treated with agents such as zinc methomyl, 50% chlorobromoisocyanuric acid or allylmorpholine. These fungicides can not only effectively control downy mildew, but also play a good role in early blight control.