Skip to content

Crown and stem rot

Also known as Crown rot, Stem rot, Collar rot

DiseaseHarmful
Raspberry plants with Phytophthora root and crown rot Photo: H. J. Larsen · CC BY 3.0 us

In short

Crown and stem rots attack the base of the plant where stem meets soil, cutting off water and nutrients. They are caused mainly by soil-borne water moulds (Pythium, Phytophthora) and fungi such as Rhizoctonia, Fusarium, Sclerotinia and Sclerotium. Wet, poorly drained mix and damaged tissue are common triggers.

How it looks

A ring or patch of brown or black tissue girdling the stem at or just above the soil line. Phytophthora can turn the lower stem black, brown or mushy; Rhizoctonia may show coarse reddish-brown threads, like spider webs, over the stem base before the tissue browns and collapses. In soft plants the crown becomes mushy and the plant falls over.

Signs

Wilting and collapse despite moist mix, yellowing and dropping of lower leaves, browning and dieback. Symptoms resemble root rot, and the two often occur together.

Life cycle

The pathogens survive for long periods in soil, reused media and debris and spread in water, soil and infected plants.

What favours it

Heavy or poorly drained media, water collecting around the crown, prolonged wet periods, warm weather, and old or contaminated media and tools.

Prevention

  • Use new, sterile, free-draining potting mix.
  • Avoid overwatering and let excess water drain freely from the pot.
  • Clean used pots (for example with a 10% bleach solution) and tools before reuse.
  • Buy healthy plants and inspect new ones before placing them with your collection.

Treatment

Start with the first step and move down only if the problem persists.

  1. Remove badly affected plants promptly with their mix; take cuttings from healthy upper growth if possible.
  2. In early cases, remove affected tissue and repot in fresh sterile mix, then water sparingly.
  3. Improve drainage and air around the base of the plant.
  4. Commercial growers use products targeted at the specific pathogen after diagnosis; follow the product label.

Pros and cons

Cons

  • Often fatal once the stem is girdled.
  • Many different causes look alike, making targeted treatment difficult without diagnosis.

Look-alikes

Root rot
Root rot starts in the roots; crown rot is centred at the soil line, though both often occur together.
Southern blight
Southern blight shows a white fan of fungal threads and tan to brown mustard-seed-like sclerotia at the stem base.
Bacterial soft rot
Bacterial soft rot is slimy and usually smells foul.

Affected plants

Many flowering plants and houseplants, for example pansies, aloe and poinsettia, as well as woody plants such as raspberry.

Sources

  1. Root, Crown, and Stem Rots on Flowers — University of Maryland Extension
  2. Houseplant Diseases & Disorders — Clemson HGIC
  3. Root Rots of Indoor Plants — University of Maryland Extension

Written in our own words from these sources. Check a product label before using any treatment.