Uneven Growth and Root Rot: Identifying and Addressing Thielaviopsis basicola
Uneven or irregular growth on a bench? Chlorotic new growth? The trouble might be Thielaviopsis root rot, also known as black root rot, caused by the fungus Thielaviopsis basicola. This disease continues to be a challenge, so be aware of the symptoms and what to do.
Uneven growth or scattered stunted plants in a seedling or liner tray, or only one to two stunted or wilted plants in a larger container or hanging basket can often indicate a T. basicola infection. Also look for plants appearing chlorotic or nutrient deficient. Before adding fertilizer, consider that compromised roots might be the cause.
Always observe the pattern of occurrence: if plants are uniformly affected, it's more likely a deficiency; if the pattern is random, it's more likely a pathogen.
Where you see irregular stunting, wilting, and/or chlorosis, check the root systems. T. basicola-infected plants will have poorly developed roots with darkened lesions. Rinse off the soil to better see the lesions. For transplants, break apart the soil to inspect how the roots are rooting into the media.
Comparing roots of healthy and sick plants can be helpful when diagnosing problems.
In some cases, foliage may appear healthy, but roots show signs of infection. Always scout incoming plant material for pests and diseases.
Pay close attention to roots of crops most susceptible to black root rot.
It's recommended to consult a diagnostic lab for accurate identification.
Thielaviopsis basicola infects a wide range of hosts, including:
- Calibrachoa
- Pansy
- Viola
- Vinca
- Petunia
- Geranium
- Diascia
- Bacopa
- Cyclamen
- Fuchsia
- Gerbera
- Begonia
High pH and over-fertilization favor this disease, so maintain a growing media pH below 5.6 and avoid waterlogged or poorly drained conditions. Fungus gnats can spread the fungus, so control them accordingly.
Fungicides are effective preventively or early in the disease's progression. Products with thiophanate-methyl, polyoxin-D, triflumizole, or fludioxonil have shown good efficacy. Sanitation is crucial for prevention, as eradicating established T. basicola can be difficult.