PPDL Picture of the Week
September 28, 2015
Black Root Rot of Pansy
Owen, PhD Student and Floriculture Technician, Purdue University
G. Lopez, Ph.D., Associate Professor & Floriculture Extension Specialist,
root rot (Thielaviopsis basicola) is
a soil-borne fungal pathogen that often infects all growth stages of pansies
during greenhouse production.
of black root rot will initially appear as black spots or bands on healthy white
roots. Early infection of black root rot is often seen at the tips of secondary
feeder root tips. As the disease progresses, the entire root system will turn
black (Fig. 1) due to the development of fungal spores within the root. For
severely infected plants, the entire root system will turn black, appear
water-soaked, and rotten, resulting in plant death.
the pansies will often exhibit chlorosis (yellowing) of the older foliage,
stunted growth, and wilting (Figs. 2 and 3). Wilting may or may not occur, but
is often dependent on the plant species and the extent of infection.
In greenhouses, the black root rot is often
introduced from infected plugs. Once in the greenhouse, the disease is
typically spread by movement of contaminated water, by wind, and other infected
plants. Additionally, black root rot favors conditions such as substrate pH above
5.5 to 6.0, moderate to high substrate moisture, excessively cool or high substrate
temperatures (56 to 77 °F) and fertility with an excess of ammonia
black root rot from entering the greenhouse environment is the first method of
control. Always examine pansy plugs carefully for symptoms of infection. If you
suspect infection, immediately submit a plant sample to a diagnostic clinic. If
the diagnosis is black root rot, ask your plug producer if they reuse their
plug trays. Reuse of pansy plug trays is not recommended as this can spread
black root rot from season to season.
black root rot during production involves the removal of infected plants and
associated substrate and growing containers. Greenhouse benches, concrete
floors, or outdoor ground covers should be sanitized with a greenhouse labeled
disinfectant. Spores can survive on benches and on plug trays.
Preventative fungicide drenches, labeled for black root rot on pansy and
when used correctly, is recommended to prevent disease development. This
information can be obtained from your County or State Extension Specialist.