   Texas Root Rot - October 28, 1998 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Given our weather last spring and summer, we probably are not complaining about the growth and production of our fruits and vegetables too much. The monsoon season brought welcome precipitation to our region at intervals that decreased our time spent watering. In fact, the rains allowed us to spend more time on weeding. The moisture also brought a "Sleeping Dragon" of the Verde Valley: Texas root rot. Texas root rot, also known as cotton root rot, is common in heavy, alkaline soils of the southwest. Heavy soils and/or caliche cause poor soil drainage. During summer monsoons, these warm, moist soils provide ideal conditions for this fungus to find a suitable host that it can parasitize. The University of Arizona Cooperative Extension diagnosed several cases of this root disease in the Verde Valley last summer. Symptoms of Texas root rot are distinctive but other agents such as gophers, other root diseases, chemicals, or mechanical damage may display similar characteristics. Plants infected with Texas root rot wilt suddenly during the summer when temperatures are high. The dead or dying leaves remain attached to the plant. After the plant has died, the root system is decayed and brown. Fungal strands may be visible on the outer surfaces of the roots and under the root bark. Fungal spore mats may or may not be present on the soil surface near the infected plant. The mats appear off-white or tan and are level with the soil surface. To be honest, it is difficult to positively identify this disease outside of a lab, but given these symptoms and knowing it is in the area make most diagnoses easier. The scientific name of Texas root rot is Phymatotrichum omnivorum. The species name, "omnivorum", means omnivorous or "eats everything". This is not quite, but almost true. Texas root rot most often shows a preference for fruit trees and broadleaf deciduous trees and shrubs. Infected apple, cherry, plum, and peach trees are most often noticed because we tend to monitor fruit crops during the growing season. Monocots (grasses, palms, yuccas, bamboo, etc.) are immune. With the exception of cottonwood and willow, most native trees are resistant. These include mesquite, sycamore, desert willow, hackberry, and many others. Gymnosperms, such as pines, spruces, cypress, and juniper are also resistant. Interestingly enough, the only resistant fruit is the pomegranate. Texas root rot spreads by root contact. A diseased root comes into contact with a healthy root and if the healthy root is from a susceptible plant, that plant becomes infected. Surface spore mats are sterile and the disease is not known to spread above ground. Some control measures have been recommended, but successful control is rare. These measures include additions of manure, and copious quantities of soil sulfur and ammonium sulfate to loosened soil surface followed by deep watering to allow leaching of the fertilizers. The net effect is to lower the soil pH and possibly to encourage beneficial soil microbes. NOTE: these treatments have been proven ineffective - there is no known treatment (Jeff Schalau, 2009). If you suspect that Texas root rot has recently paid you a visit, now is the time to stop mourning and go to work. Possibly the best course of action is to remove the infected plant(s), treat the soil as stated above, and wait a full growing season before replanting. Resistant species are the best choice, but just as humans repopulate known flood plains following the floods, we will continue to replant susceptible species where we have had recent bouts with Texas root rot. If you have done this, avoid over watering and pray for beneficial soil microorganisms (i.e. mycorrhizae, see Back Yard Gardener October 14-16, 1998). The University of Arizona Cooperative Extension has several publications on plant diseases. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |