7/2/2024 - By Dr. Aaron Palmateer

Among the vast amounts of potential pathogens and diseases that your plants are susceptible to, Rhizoctonia is one of the most varied to watch out for. In this article, we will dive into where the pathogen comes from, the ways it can harm/affect your plants, and the options you have for control throughout the season.

What is Rhizoctonia?

Rhizoctonia species are among the most diverse of the fungal pathogens and are notorious for causing diseases in seedlings including pre- and post-emergence damping off. Rhizoctonia is one of the most common pathogens associated with ornamental plant production in greenhouses and nurseries attacking both containerized and field-grown plants. Rhizoctonia usually attacks plants at the soil line, causing root and stem rot, which results in girdling and death of the tops, but this pathogen can also attack leaves causing an aerial blight. Rhizoctonia is especially severe when plants are grown close together and kept moist.

Effects of Rhizoctonia

Rhizoctonia is common on bedding plants including garden impatiens, New Guinea impatiens, vinca, dahlia, and pansies, but also on ferns especially Boston ferns, succulents including echeveria and woody ornamentals such as boxwood and gardenia. Affected roots become brown, mushy, and disintegrate. With abundant moisture, high relative humidity (80 – 90%), and temperatures ranging from 68 – 86 ℉, Rhizoctonia can move up in the plant canopy causing brown, irregularly shaped spots that form anywhere on the foliage and stems. Sometimes web-like brown mycelium of the pathogen will cover infected portions of the plant causing aerial blight.

Controlling Rhizoctonia

If possible, eliminate overhead irrigation in covered houses or exposure to rainfall for outdoor plants. Water plants during the day when plant leaves have the greatest chance to dry quickly. Root rot caused by Rhizoctonia appears much like root rot caused by other pathogens, so an accurate laboratory diagnosis is important to ensure the specific pathogen you are dealing with, especially when applying any chemical products.

A few of the recommended fungicides for control:

-          Chipco 26GT, 26019

-          T-Methyl

-          Concert II

-          Avelyo, Tebuconazole, Propiconazole

-          Postiva

-          Medallion, Emblem

-          Palladium

-          Azoxy 2SC, Fluoxastrobin SC

-          Broadform, Orkestra Intrinsic, Pageant Intrinsic, Mural

For example, fungicides that control Pythium, another common root rot pathogen may work for Rhizoctonia, but tests are important to be sure. You must also keep in mind that mixed infections (Pythium and Rhizoctonia together) are common, only an accurate diagnosis will allow you to choose the best and most complete control strategies. Be sure to monitor plants for above-ground symptoms of root rot including yellowing or pale green leaves, small leaves, wilting, and stunting.

Reach Out to Your Harrell’s Representative

Identification and management of plant disease are pivotal to running a smooth and healthy operation and starting clean and staying clean. Your Harrell’s Rep is here to help you identify, control, and protect your plants throughout the season. Reach out to your Rep today with all your questions, if you need any recommendations, or just to connect. We are here to help!

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