What Is Rhizoctonia Fungus and What To Do About It?

The soil-borne fungus known as Rhizoctonia fungus disease is abundant in outdoor soil in every setting from home gardens to commercial agricultural enterprises.

This fungal infection produces plant growths known as sclerotia.

These brownish-black structures are very tough and allow the fungal infection to lie dormant in the soil or within an infected plant for many years.

drawing of rhizoctonia fungal disease

What Plants Are Susceptible To The Rhizoctonia Fungus?

Rhizoctonia can infect a wide range of host plants and cause many different diseases such as:

The most common type of Rhizoctonia this fungus is soilborne and known as Fungus Rhizoctonia solani (teleomorph Thanatephorus cucumeris).

This Rhizoctonia species is the major cause of stem rot in cuttings.

This is especially true of cuttings frequently misted.

Young plants are more susceptible to Rhizoctonia.

Because this fungus dwells in the upper level of the soil, it is very likely to cause Rhizoctonia root rot in plants upper layer in plants’ upper roots.

Furthermore, R. solani can infect seeds sown on the surface of the soil or just below it.

This means plants will be infected post-emergence before they even germinate.

When they emerge, they will be subject to damping off.

While it is possible for older plants roots to become infected with root diseases, it’s far more common for Rhizoctonia to infest the tender young roots of seedlings.

Fungicide seed treatments are effective in this situation.

When roots are infected with this fungus, they become mushy and brown just as they would with other types of root rot plant pathogens.

R. solani also survives as mycelium by colonizing soil organic matter.

How Can You Tell If Your Plants Or Cuttings Are Infected With Rhizoctonia?

Because this type of fungal infection dwells at the upper surface of the soil or growing medium, it usually attacks plants’ stems at soil level.

When Rhizoctonia sets in, your plant will suffer from nutrient deficiencies because nutrients are not able to travel through the structures of the plant.

Stems having been infected with Rhizoctonia look shriveled, dry and wiry.

If you notice the stems of your plants or cuttings are decaying very quickly beginning with the formation of reddish-brown lesions or plain brown lesions, you should suspect Rhizoctonia.

Typical development for these lesions involves enlarging and then forming sunken cankers right at the soil line.

As the cankers enlarge, they surround and gird the stem and restrict the movement of nutrients and water within the plant.

This causes wilting in the plant or cutting, especially during hot weather.

How Does Rhizoctonia Get Into A Plant?

This fungus can infect your plant in numerous ways including:

#1 – Through Moisture

When wet leaves come in contact with the soil, Rhizoctonia can gain access and cause a condition known as Aerial Blight.

If your plants’ leaves are wet, or if your plants are too close together or otherwise have poor air circulation, Aerial Blight will spread very quickly.

In a greenhouse setting, high humidity will facilitate this spread.

#2 – Through Garden Soil

If you purchase professionally prepared growing media (and especially soilless growing media), you’re unlikely to have problems with Rhizoctonia.

This is because these products have been thoroughly processed and pasteurized to kill off contaminants.

You need to be careful, though. Introducing even a small amount of natural soil or mineral soil can cause problems.

For example, you may have potted plants and professionally prepared growing media with pots or containers sitting directly on the soil.

When you water, Rhizoctonia splashes up from the soil into your containers.

This will contaminate the growing medium and the plant.

#3 – Via Dust

Furthermore, Rhizoctonia is carried in on dust from the outdoors.

If you live near a dusty road or construction site, take steps to prevent having dust settle on your plants.

#4 – By Insects

Pests such as sure flies and fungus gnats carry Rhizoctonia from plant to plant so pest management is important combined with good cultural practices.

What Conditions Cause or Compound Rhizoctonia?

Rhizoctonia does best in hot temperatures ranging from 70° – 90° degrees Fahrenheit (21° C – 32° C).

For this reason, you’re sure to find it to be more of a problem late in the springtime and throughout the summer.

Rhizoctonia thrives in moderate soil moisture.

It does not do well in very dry settings or very wet and saturated conditions.

High humidity is ideal for Rhizoctonia growth as it tends to grow on the surface or just below the surface of the soil.

High humidity also allows Rhizoctonia to travel quickly over plants, and you may even see brown webbing on the surface of the affected parts of the plant.

Lack of airflow, crowded plants, wet leaves, overhead watering, and frequent misting of plants will encourage Rhizoctonia to develop.

Very young plants with tender plant tissue are very subject to infestation by this fungal infection.

Additionally, plants recently cut or broken (especially near the soil line) are subject to infestation.

12 Tips: What Can You Do About Rhizoctonia?

A fungicide prepared as a soil drench can have a strong effect on Rhizoctonia, but as with most fungal Rhizoctonia infections, it’s better to prevent it than to treat it.

An accurate diagnosis is crucial because fungicides controlling Pythium do not control Rhizoctonia and visa versa.

Maintain these conditions to discourage the growth of this fungus:

#1 – As much as possible, keep the ambient temperature around your plants at 70° degrees Fahrenheit (21° C) or lower.

Remember soil temperatures higher than 70° degrees Fahrenheit (21° C) provide conditions conducive to the growth of Rhizoctonia and a number of other fungal and bacterial infections.

#2It’s best never to reuse growing medium, but if plants are infected with any fungal infection, you should take dramatic steps to get rid of the infected soil and treat the surrounding area.

#3Remove and dispose of diseased or infected plants and surrounding plant residue immediately to begin disease control.

Never dispose of any plant with any plant diseases or disease symptoms in your compost heap.

Instead, burn them or seal them up in plastic and put them out with the trash.

If not, when you use the compost later you’ll see disease development again.

#4It’s best to use brand-new pots and containers.

If you must reuse a planting container, be sure to sanitize it completely.

Scrub it with hot, soapy water and rinse with a bleach solution.

Allow the container to air dry thoroughly in the sunshine.

#5 – Avoid allowing plant leaves to come in contact with the soil as this will give Rhizoctonia access to your plant.

#6 – Avoid overhead watering, and always water in the morning so excess water will have a chance to dry up before the sunsets.

#7 – Keep plants properly pruned to increase the airflow among the leaves.

#8 – Place plants the correct distance from one another to increase airflow and prevent moisture buildup.

#9 – Take steps to maintain humidity levels well below 93%.

#10 – Avoid plant injury and do not allow your plants to become stressed by overwatering or under-watering.

#11 – Don’t let the end of your water hose touch the soil, and don’t get natural soil into your plant containers.

#12 – Always sterilize all of your gardening equipment thoroughly after each use.