Your small, versatile yaupon hollies that usually exhibit good resistance to pests and diseases are still susceptible to cotton root rot disease, referred to as a "silent killer," according to the AgriLife Extension Texas A&M System. Resistant does not mean immune. When temperatures rise, the threat increases as fungal pathogens become active. With appropriate care and attention to culture, avoiding this problem becomes less challenging.
Vigorous, well-cared for yaupon hollies (Ilex vomitoria) are more likely to avoid infection by cotton root rot fungal pathogens in comparison to neglected plants in a weakened state as stressed resistant plants lose their ability to resist pathogens. Grow yaupons in full sun to partial shade for best growth, according to the University of Florida IFAS Extension. Yaupons thrive in a wide variety of soils including both clay and sand with a tolerance to salt and wet sites.
Cotton root rot of yaupons is a fungal infection with soil-borne pathogens living deep within soil. The fungi develop into thin, fibrous strands that ascend toward the surface, contacting and infecting yaupon roots, according to the AgriLife Extension Texas A&M System. Infection generally occurs in warmer conditions when soil temperature reach or exceed 82 degrees Fahrenheit. Cotton root rot pathogens prefer soil with a pH of 7.0 to 8.5.
Particularly if your yaupon is already stressed, infection may occur on this otherwise resistant holly. Once above-ground symptoms appear, roots are already damaged. Visible symptoms above the soil line include wilted foliage and discolored leaves that become a bronze hue. Roots change to a brown color as they decay and the fungal strands that infected the roots remain attached, according to the AgriLife Extension Texas A&M System. Since rotten roots can no longer absorb water and nutrients necessary for yaupon life, your plant will die. Infection and death are rapid, often occurring within only a few days.
Choose resistant plants when re-planting where an infected yaupon has been removed or if you suspect soil is infected. Other resistant holly plants include the English holly (Ilex aquifolim), American Holly (Ilex opaca), Dahoon holly (Ilex cassine), according to the AgriLife Extension Texas A&M System. Other plants like cedar elms, live oaks and sycamores are also resistant. Maintaining a home garden full of resistant plants lowers the likelihood of infection and spreading of fungal pathogens. Contact your local county extension agent to determine which trees exhibit the best resistance in your region.
No particular chemical or natural control method is available for complete management of cotton root rot disease. However, in conjunction with planting resistant options, the best control is to amend your soil with a steady addition of organic content to lower the pH level and increase the healthy nutrient content, according to the AgriLife Extension Texas A&M System.