About Crown Rot
Crown rot is a disease caused by a variety of soil-borne fungi (Pellicularia rolfsii, Sclerotium delphinii, and Sclerotium rolfsii), affecting mainly herbaceous and woody plants. These fungi overwinter in soil and are capable of surviving in soil for long periods of time. They infect a host through spread of contaminated soil, tools, flowing and/or splashing water, and transplants. Air transmission is much less common for this disease due to its high moisture content. Once a host is infected, crown tissue will begin to deteriorate and rot, causing leaves to brown, fall off, and die. This process occurs as a result of the pathogen restricting water flow through the stem of the plant. Yield loss in infected plants is common due to the severity of the pathogen. Highest yield loss tends to occur in seasons with a moist start, followed by a dry finish. With a moist start to the season, fungi are able to spread quickly, while a dry finish to the season enables moisture stress, which helps the pathogen grow within the plant.
Crown Rot Identification and Habitat
Crown rot commonly infects plants starting at their base, and then spreads upwards throughout the plant. One of the first indicators of crown rot will be the brown tiller bases that develop. As the season progresses, these will become increasingly visible. Whitehead formation is also common, especially in season beginning with a moist start and ending with a dry finish. In conditions with high humidity, cottony webbing can grow and will spread to the base of the stem and the soil around the plant. Sclerotia development can occur at the base of the plant and, in abundance, can form a crust on surrounding soil. Overall crown tissue of the plant will likely be wilted and change to a yellow or red color. By mid-season, it should be noticeable that infected plants are stunted in growth and have nutrient deficiencies due to the pathogen. Upon close examination, plant tissue will be soft and brown.
Crown rot development peaks in environments with hot temperatures, high humidity, and periodic rains. More specifically, temperatures between 86 to 95 degrees F will favor crown rot growth the most. Temperatures below 70 degrees F will be less favorable for crown rot development. Habitats with lots of splashing rain and water flow will allow for rapid spread of the pathogen. This disease is capable of infecting a wide variety of plants through water transmission. Crown rot can survive in soil for long periods of time, so be wary of underground fungal development and spread, especially in soil with high moisture. This is why the disease will typically infect the base of a plant first. Cool and dry conditions will deter the development of Crown rot severely.
Crown rot Management and Control Methods
With crown rot it is crucial to remove infected plants immediately after symptoms are detected in order to limit the spread of the pathogen. After the diseased plants are removed, dispose of plants properly, and be sure to avoid composting them as the pathogen will survive if composted. Additionally, excavate the soil around the infected plant to a depth of 8 inches and width of 6 inches past the diseased area. This will help reduce the chances of the disease spreading to other plants. Furthermore, solarizing the soil can be an effective, organic way of dealing with pathogens left in the soil. Make sure the area receives a few hours of direct sunlight per day, and leave it covered with a clear plastic for two or three months in the summer. Reducing excessive soil moisture by improving drainage can help to limit growth and dispersal of crown rot. Lastly, keeping tools clean is important to reduce overall spread of disease from plant to plant when in the field.
For crown rot, fungicides are the most common chemical control method. Fungicides thiophanate methyl and Mancozeb are good for dealing with crown rot. Consult the label for application guides and cautionary procedures. Fungicides will be useful in prevention of the disease, but will be less useful once the disease has completely infected the plant.
Alternative Crown Rot Names