Radishes are one of the easiest crops to grow. From seed to harvest often takes just a handful of weeks. But, just as with any plant, radishes can develop disease symptoms that can affect the harvest. Cercospora leaf spot of radish is one such disease that can cause seedling death or, in older plants, reduce the size of the edible root. The disease is harbored in soil and in cruciferous plants. Learn about radish Cercospora management and what you can do to prevent the disease.
Recognizing Cercospora Leaf Spot of Radish
If you had a nickel for every potential disease or pest issue that could affect your vegetable patch, you would be rich. Radishes are fairly hardy plants but even they are prone to disease. One of the common diseases is cercospora leaf spots on radish, also known as early blight. It resembles many other leaf spot diseases, unfortunately, so can be difficult to diagnose. Luckily, it is fairly easy to prevent.
A fungus causes radishes with cercospora leaf spot. The disease starts out on leaves but moves quickly to petioles. Leaves develop large round lesions of gray or brown with dark margins. The petioles become infected and exhibit long lesions of greenish-gray. The leaf lesions become lighter in the center as they mature.
As the infection progresses, the entire leaf will become yellow and will eventually die and fall off. This is a very contagious fungal disease and can spread rapidly to all the leaves on a plant. The lack of photosynthesis to drive cell formation means the root size is drastically diminished. Soon after all the leaves fall off the plant will die.
Cercospora fungus lives in soil or discarded plant matter. It can survive thus over the winter. It may also survive in volunteer plants, certain weeds and wild cruciferous plants such as wild mustard. The fungus also affects other members of the Cruciform family such as cabbage, but can also infect watermelons, beets and many more vegetable crops.
The spores of the fungus form on leaves and survive as dropped foliage. Even once the leaves have composted, the soil can still harbor the fungus. Temperatures of 55 to 65 degrees Fahrenheit (13 to 18 C.) promote the growth of the spores. These are splashed onto plants during rain or irrigation. They may also be carried by wind or during cultivation. Good sanitation practices are crucial to radish Cercospora management.
Cercospora leaf spots on radish can be controlled with cultural and sanitation methods. Several fungicides are also useful if used early in the disease cycle. One which is safe to use on edible crops is copper sulfate.
Other practices useful to prevent infection are a 3-year crop rotation and sanitation of equipment. Deeply plowing under plant debris can help reduce the risk of infection since radishes do not grow very deep in soil. At the end of the season, remove all plant material even if there was not a current year infection.
During the growing season, remove any plants that exhibit symptoms. Remove weeds and keep other cruciform vegetables away from the radish crop. Provide good spacing between radishes to promote air circulation and prevent infected plants from spreading the disease to the whole crop.
Cercospora can infect other types of produce, so early detection is key to controlling the spread of the disease.