My Rose Stems Are Turning Brown Near the Roots

Symptoms

• Yellowing or browning of leaves followed by sudden wilting is the most obvious symptom of cotton root rot. The fungus grows through the soil, infecting and rotting roots as it feeds. If soil conditions are moist, the fungus grows up through the soil, often covering lower stems and the soil around them in a mat of powdery brown growth. Large, established bushes may take longer to die than smaller bushes, but death is inevitable.

Conditions

• Although this fungus attacks around 2,300 host plants, it does not attack any grasses or coniferous hosts. It is found only in the southwestern U.S. in soils that are alkaline or devoid of organic matter. It prefers warm weather, most symptoms occur when soil temperatures are above 82 degrees F. It is not spread above ground by spores but has to move from plant to plant via infected roots.

Disease Cycle

• The active fungus rests in the soil, sending out root-like feelers that grow until they contact plant roots. Once roots are contacted these feelers wrap around the roots and use them to climb toward the surface. At the surface the root bark is destroyed and the fungus invades the plant, killing it quickly. When its host plant dies, and no others are available, the fungus forms a hard shelled structure called a sclerotia that encases spores. These sclerotia enable the fungus to survive in the soil without a host for many years.

Control

• There is no cure for cotton root rot and replacing your roses with a resistant variety may be the easiest way to ensure success. If you want to keep roses in that spot you can amend the soil with compost or other organic matter prior to planting. Texas A&M recommends planting barrier crops, like ornamental grasses around your roses to help keep the fungus at bay. Infected plants may be saved by treating them with ammonium sulfate. Prune the rose bushes and build a soil ridge around it at a few feet out from the main stems. Add 1 pound of ammonium sulfate per 100 feet of row to the bushes and fill the inside of the ridge with 4 inches of water. Repeat in 5 to 10 days but don't apply ammonium sulfate more than twice a season.