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Index : Plant Diseases
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- 3. Texas Root Rot - Top
- Trees and shrubs that are seemingly healthy one day and completely dead the next have most likely died from a disease called Texas Root Rot. Also known as Cotton Root Rot because of it's prevalence in cotton fields, it is by far the most common disease of landscape plants in the desert Southwest. It's also found in Texas, but there they prefer to call it "Arizona" Root Rot. I'm not sure which they call it in New Mexico.
Texas Root Rot is usually seen during the spring and summer months when temperatures are hot. The fungus that causes the rot exists in the soil and attacks the root system of susceptible trees and shrubs. As the root system dies, water is no longer conducted to the leaves and the plant wilts. When temperatures are hot and the demand for water is high, this wilting occurs rapidly. Some plants may die over several days, others may literally die overnight.
Another distinguishing characteristic of Texas Root Rot is that the dried leaves cling onto the branches for weeks rather than dropping off within a few days as would be normal. During rainy periods, the fungus may grow out of the ground and develop a fungal spore mat that looks something like poured pancake batter. But in most cases the spore mat does not develop. Unlike most fungus diseases, this spore mat is sterile and will not spread the disease. Movement of the fungus is only underground in the soil.
There is no soil test for Texas Root Rot. The disease organism can be present in the soil but dormant lie dormant for years, even decades. Then when conditions are right and a host plant is present the disease can spring back to life and begin infecting plants.
Many desert plant species, such as Palo Verde and Mesquite are tolerant of Texas Root Rot. Tolerant means that they are not likely to be attacked by the disease but in some cases they can be. The only non-desert trees known to be tolerant of Texas Root Rot are Live Oak and all types of citrus trees.
A small group of plants are actually immune to Texas Root Rot. They include palms, agaves, grasses, yuccas, aloes and an assortment of a few other small plants. Immune means that they will not be effected by the disease. These are the ones that should be planted back into an area where a plant is known to have died of Texas root rot.
According to UA Plant Disease Specialists there is no known control for Texas Root Rot. The old recommendation of mixing sulfur, manure and ammonium sulfate into the ground to prevent or cure the disease just doesn't work. The only way to avoid the disease is to plant immune or tolerant plants, or just take your chances that the disease organism is not present in your soil.
Susceptible plants should not be planted in areas where Texas Root Rot has occurred. Trees such as fruit and nut trees (except for citrus), ash, elm, fig, sycamore, bottle tree, silk oak, pepper tree and African sumac are considered very susceptible. Many shrubs including pomegranate, xylosoma, cassia, Mexican bird of paradise, oleander and roses are also very susceptible.
The only way to determine if a plant has died of Texas Root Rot, other than sudden wilting and clinging of the leaves, is by examining the roots under magnification. Light brown strands or hyphal webs of the fungus can be seen on the surface of the roots.
If you have a plant that has just died and you suspect Texas Root Rot you may bring a sample of the roots to the Pima County Extension Plant Clinic at 4210 N. Campbell Avenue for diagnosis. Take several samples of rotting and discolored roots on which the outer cortex layer still remains attached. The samples should be pencil size or slightly larger and at least 6 inches long. Leave soil attached and keep the roots refrigerated in a plastic bag until the sample can be brought in for analysis. This service is offered to the public at no charge.
"Improving Your Drip Irrigation System" will be the topic for this week's garden demonstrations. They will be presented on Wednesday at 9 a.m. at the Pima County Extension Center, 4210 N. Campbell Ave (central); and at 1 p.m. at the Wilmot Library (east), and on Friday at 1 p.m. at the Oro Valley Public Library (northwest).
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: September 7, 2003
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