We’ve probably all lost seedlings to damping-off disease. Nascent stems, healthy only the day before, suddenly appear pinched and broken, never to recover. When lesions appear further down the stem at the soil line, it is called collar rot.
Collar rot gets its name because of the lesions that form a collar around where the root system meets the stem. In embryonic plants, this area between the first root (radicle) and the first stem (hypocotyl) is called the collet. In more mature plants, this area is called the crown.
Vulnerable stems and seedlings
In the case of both damping-off disease and collar rot, pathogens enter delicate new stems as they emerge from the earth, scratched by soil particles. These tiny wounds provide points of entry. Insect and herbivore feeding, garden tools, and rubbing due to overcrowding and improper pruning can also create these wounds. Wounds heal quickly, but sometimes pathogens get in. When they do, problems begin.
Collar rot symptoms
As fungi, bacteria, and other pathogens enter a plant, lesions start forming in a band, or collar, around the lower portion of the main stem. At the same time, vascular bundles become blocked and the disease-causing agents begin multiplying.
Collar rot pathogens
Collar rot looks similar to damping-off disease because the same pathogen may be responsible. Collar rot can also be a symptom of several other infections. Trees infected with fireblight tend to be more susceptible to collar rot, but we don’t know why. As you can see, collar rot isn’t a specific disease. Instead, it is a symptom of attack by several different pathogens:
Collar rot prevention
Collar rot occurs in gardens and containers where the soil is infected. You can prevent the infections that cause collar rot with these tips:
I hope collar rot never occurs in your garden.
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