Black root rot is looked upon as the most destructive worldwide disease of crucifers like radishes. This bacterial problem only affects crucifers and causes a range of harmful results. Become familiar with signs to look for as well as reliable control methods for safe, healthy growth of radish crops in your home landscape.
Black root rot of radishes and other crucifers is caused by the bacteria Xanthomonas campestris pv. campestris (Xcc). Other highly susceptible plants include cabbage, broccoli, kale, turnips and rutabaga among other crucifers, according to the University of Kentucky Cooperative Extension Service. Black root rot bacterial pathogens are seed-borne and spread through transplanting, rain or infected plant parts transferred by the wind.
Symptoms and Damage
Black root rot infection of radishes, more often referred to simply as black rot, results in the display of V-shaped areas on plants that turn yellow and then brown as the diseases progresses. Discolored areas of plant tissue die and become delicate, and leaf veins darken to an almost black hue, according to the University of Kentucky Cooperative Extension Service. Roots and stems may also blacken and rot, according to the Cornell University Vegetable MD Online. Infection results in stunted growth and, when infection is of a seedling, the plant will fail to develop.
If your radishes are affected or destroyed by black root rot, choose to grow resistant crucifer varieties in their place to avoid future problems. Resistant varieties are not immune but have a much higher chance of providing your home garden with a productive growing season. Some resistant varieties include, but are not limited to, the cabbage varieties Atlantis, Bronco and Ramada as well as broccoli plants Arcadia and Greenbelt, according to the University of Kentucky Cooperative Extension Service. If you choose to keep your radishes, planting resistant varieties will still lower the likelihood of infection as your radishes will not be surrounded by susceptible plants.
For natural control, first realize that radish (Raphanus sativus) and wild radish (R. raphanistrum) are both susceptible to black root rot. Maintain strict sanitation by cleaning all tools or equipment that come into contact with your radishes and other crucifers, according to the University of Kentucky Cooperative Extension Service. Plant disease-free radish seeds or transplants to prevent the introduction of black rot into your home landscape. Plant in well-drained soil to avoid wet conditions that promote the spread of bacteria.
Chemical Control Effectiveness
Copper-based fungicides are often used as an attempt at chemical control, but results are inconsistent. Though chemical control is not as effective as the planting of resistant varieties, when dealing with susceptible radishes, control is in greater demand. As a preventive method, you may try a chemical control program of applying copper hydroxide or fixed copper once a week, according to the Cornell University Vegetable MD Online. For appropriate chemical application, contact a licensed professional or your local county extension agent.