Black Root Rot
Black root rot is caused by the fungus Thielaviopsisbasicola. The disease isn`t common on vinca
in landscapes, but can be introduced by planting infected material or planting
in areas where other, more susceptible hosts, such as pansies, have succumbed.
As with all root rot diseases, infected plants are stunted and turn yellow.
Washing and inspecting the root systems can point towards a black root rot
diagnosis. Diseased plants have small root systems with a “salt-and-pepper”
appearance. The root color results from the presence of dark fungal growth and
black resting spores growing within the roots. As the disease becomes more
severe, roots turn black and soft.
Avoid planting vinca in areas
where pansies have performed poorly or where Japanese hollies have died. Select
plants with a healthy green appearance and uniform height. Fertilize according
to soil test results, avoiding fertilizers with high ammonium content, such as
ammonium nitrate or ammonium sulfate. High pH soils can lead to increased
disease severity so apply lime only if needed. Remove and destroy all infected
plants, including the entire root system. Thiophanate methyl (such as Cleary`s 3336-WP Turf & Ornamental Fungicide or Southern Ag
Thiomyl Systemic Fungicide) can be applied to protect remaining plants.
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