Plant Disease Notes - Black Root Rot Of Pansy
ANR-1053, New July 1997. By Jeff Michels, Graduate Assistant; Austin Hagan, Extension
Plant Pathologist, Professor; and Edward Sikora, Extension Plant
Pathologist, Associate Professor; all in Plant Pathology at Auburn University.
Plant Disease Notes
Black Root Rot Of Pansy |
Black root rot, caused by the fungus Thielaviopsis basicola
( also known as Chalara elegans), is a widespread and destructive
root disease of pansy. In Alabama, the disease is common on both landscape
and nursery pansies. The disease can be a problem with other floral crops
including cyclamen, hybrid impatiens, poinsettia, and annual vinca. Black
root rot is most prevalent when conditions are stressful to the host plant.
Symptoms. Pansies infected with black root rot produce aboveground
symptoms that are typical of other root rotting diseases and include stunting
and/or wilting of plants and yellowing (chlorosis) of the foliage. In early
stages of the disease, the roots, which are normally white, develop dark
spots or bands. Early symptoms may be more prevalent in secondary feeder
roots. Dark-colored spores can be seen on blackened regions of infected
roots with the aid of a magnifying glass or microscope. In advanced cases,
the root system becomes black and water-soaked. The disease is a problem
during all stages of growth and be can especially destructive during the
late summer months when temperatures are high.
Persistence And Transmission. Black root rot is caused by the
soilborne fungus T. basicola. The fungus is spread when healthy roots
come in contact with infected roots or infested soil. Spores of the fungus
can also be spread from pot to pot by splashing water. The disease is sometimes
spread when infected plugs (which often appear healthy) are introduced into
a new landscape or greenhouse area. Always examine plugs carefully for uneven
growth, poor foliage color, or other symptoms of the disease before being
introduced into a new area. Black root rot fungal spores are known to survive
in greenhouses up to 2 months and can also survive in plant debris under
benches.
Control. A combination of good sanitation, proper plant care,
and fungicides can help retard the development of black root rot. Black
root rot is best controlled by using the following strategies:
- Use fresh soilless potting mix.
- Use new containers for each planting.
- Keep equipment and planting area clean of old potting media.
- Apply the rate of nitrogen recommended for pansy or other floral crops.
- Avoid fertilizers high in ammonium as a nitrogen source.
- Adjust potting media to a pH between 5.0 and 5.5.
- Avoid high temperatures, especially in the late summer.
- Check your plants regularly for uneven growth and signs of black root
rot.
- Discard infected plants.
- If needed, use a fungicide recommended for control of black root rot:
-thiophanate-methyl--Cleary's 3336 50W 12-16 oz per 100 gallons or
Cleary's 3336 42F 1.5 pt. per 100 gallons. Soil drench : Apply every 2
to 3 weeks.
Use pesticides only according to the directions on the label. Follow
all directions, precautions, and restrictions that are listed. Do not use
pesticides on plants that are not listed on the label.
The pesticide rates in this publication are recommended only if
they are registered with the Environmental Protection Agency and the Alabama
Department of Agriculture and Industries. If a registration is changed or
cancelled, the rate listed here is no longer recommended. Before you apply
any pesticide, check with your county Extension agent for the latest information.
Trade names are used only to give specific information. The Alabama Cooperative
Extension System does not endorse or guarantee any product and does not
recommend one product instead of another that might be similar.
For more information, call your county Extension office. Look in your telephone
directory under your county's name to find the number.
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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