What is Rhizoctonia Carnation Rot?
If you have rotting carnation plants, you may have the fungus, rhizoctonia. This stem rot on carnations can be prevented by using sterilized soil, but the fungus often reinvades. It is most prevalent in warm, moist conditions, just when your plants are blooming. It can kill the plant in severe infestations and the right conditions. Once rhizoctonia carnation rot is present, treatment may be ineffective. The fungus responsible overwinters in soil. It attacks many ornamental and crop plants. The fungus may be transmitted by fungus gnats but also moves on wind and is transmitted on clothing and tools. Just a small bit of the mycelia or sclerotia is enough to infect healthy plants. The disease can also come from stem cuttings of infected plants. In areas with high humidity, moist soil and warm temperatures, carnation rhizoctonia stem rot is especially damaging.
Symptoms on Carnations with Rhizoctonia Stem Rot
The first signs will be wilting, yellowing foliage which can mimic many other diseases. Rotting carnation plants may have mycelia or grayish black rot at the soil line. The fungus cuts off water and nutrients at the stem, effectively girdling the plant and killing it. Stem rot on carnations does not affect the roots but will cause the plant to starve and die of thirst. If plants are closely planted, the fungus spreads readily among them and can also attack other types of flora.
Preventing Rhizoctonia Carnation Rot
There doesn’t seem to be an effective treatment once plants have the fungus. Pull up and destroy infected plants. Inspect nursery plants carefully before bringing them home. Prevention is through sterilization of tools and containers, using sterile soil and fungal soil drenches. If the disease has been present in beds in seasons past, solarize the soil prior to planting. You can easily do this with black plastic over the bed for several months. As long as the top few inches (8 cm.) get nice and hot, the fungus can be killed.
