By: Amy Shi, Research Associate, Ontario Ginseng Growers Association
Rhizoctonia is showing up in ginseng gardens. The symptoms of Rhizoctonia crown rot in ginseng include expanding circles (up to 1 m in diameter) of collapsing tops that often arch over as the lower stem decays. The lower stem within or below the straw and/or the crown of affected plants can have orangish-brown soft rot symptoms (Figure 1).
Figure 1. Symptoms of Rhizoctonia crown rot include softening and browning of the lower stem within the straw.
Have you ever wondered if that suspicious patch on your ginseng is caused by Rhizoctonia solani? Here’s a quick and surprisingly easy experiment you can do right at home—no lab coat required. Just a few basic supplies, a little curiosity, and one night’s wait.
What You’ll Need:
A sealed container or Ziploc bag
A piece of moist tissue (not dripping, just damp)
A toothpick
A fresh ginseng root with symptoms or suspected to be affected by Rhizoctonia (preferably with an intact crown)
What to Do:
Gently insert the toothpick into the crown area of the ginseng root—this is where infections tend to hang out.
Place the root and toothpick onto the moist tissue inside your container. Seal it up to maintain humidity. If using a Ziploc, ensure there is some air space around the root.
Leave it at room temperature overnight.
What to Look For:
By the next morning, take a peek. If you see white, fluffy threads (called mycelia) crawling up the toothpick or spreading from the crown (See Figure 2), you are most likely looking at Rhizoctonia solani in action. Rhizoctonia is fast-growing, so it can outpace most other fungi.
Figure 2. The toothpick test for Rhizoctonia solani after one night in a moist chamber. Note the fluffy mycelial growth near the crown of the root.
This fungus thrives in cool, moist conditions, so the setup is perfect for encouraging its growth—at least for a short while.
But Here’s the Catch:
Timing is everything. If you wait too long—say more than 24 to 36 hours—other slower-growing fungi can crash the party as they catch up to the Rhizoctonia. That makes it hard to tell who’s who, especially since several soil-borne fungi produce similar mycelial growth.
The Science Behind It:
Rhizoctonia solani is a soil-borne fungal pathogen known for causing damping-off, root rot, and crown rot in many plants, including ginseng. It’s a member of the basidiomycete group, and its hyphae (those thread-like structures you’ll see) are typically wide, with 90° branching angles—a clue for identification under a microscope.
