Cotton root rot in plants is a devastating fungal disease. What is cotton root rot? This disease is caused by the fungus Phymatotrichum omnivorum. “Omnivarium” indeed. The fungus colonizes the roots of a plant, gradually killing them off and reducing its health. This voracious fungus is one of the most destructive diseases of cotton and over 2,000 other plants. Read on to learn more about it.

Cotton Root Rot Symptoms

Ornamental, fruit and nut trees, cotton and alfalfa are among the plants susceptible to cotton root rot. Fortunately for northern gardeners, the fungus that causes the disease is limited to the southwestern regions of the United States. Sadly for these gardeners, the fungus lives for years in soil and has the ability to kill even tall trees. It is important to recognize cotton root rot symptoms since correct identification of the disease is key to control.

 

Cotton root rot in plants is most prevalent in the summer months, from June until September. The fungus needs high summer temperatures and calcareous clay soil. The affected plant wilts and experiences foliar color changes, from green to yellow or bronze. Death is very sudden in warm weather once the fungus colonizes and fully invades the roots. Cooler weather can slow the decline of the tree, but once the warm season hits, it will invariably die.

Identification of the disease can be done by removing the dead plant. The roots will have wooly strands of fungus and a defined decayed appearance.

Treatment for Cotton Root Rot

Treatment for cotton root rot after infection has been achieved on occasion with good cultural care. Prune the tree or plant back, working ammonium sulfate into a trench built around the tree and water thoroughly. Only 2 treatments may be applied per season and it isn’t a cure; only some plants will come out of the wilt and survive.

The acidification of soil creates an unfavorable environment for the fungus. Fertilizers high in nitrogen can minimize the spread of the disease. Chemical sprays do not exist for control of cotton root rot.

Prevention of Cotton Root Rot in Plants

Because there are no sprays or formulas to kill the fungus, planning ahead in zones prone to the disease is essential. The only way to control cotton root rot is to purchase resistant plants or use plants that have resistance to the disease as barriers. Use monocotyledonous plants such as grasses and wheat, oats and other cereal crops as organic amendments.

Once the fungus is in the soil, it can survive for years and lives at the level at which most plants have a concentration of roots. This is why it is important to avoid plants susceptible to cotton root rot. These include:

• Fruit and nut trees
• Ash
• Cottonwood
• Elms
• Figs
• Sycamore
• Bottle tree
• Silk oak
• African sumac
• Pepper oak
• Oleander
• Bird of paradise
• Roses

Choose instead plants with some natural resistance as landscape ornamentals. Plant that seem to tolerate soils penetrated with the fungus with no ill effects include:

• Evergreen conifers
• Cactus
• Jojoba
• Hackberry
• Palo Verde
• Mesquite trees