Q What is pansy sickness?
A This is a soil-borne disease, also known as stem rot. It is caused by the fungus-like organism Pythium violae, related to the species that causes damping off in seedlings.
Caption: Plant pansies and violas in a different area of the garden each year
Q What plants does it affect?
A This species of pythium can affect any plants in the viola genus, though it is normally seen in bedding pansies or violas. It also occurs as a secondary infection in carrot cavity spot, where it causes root rotting.
Q How do I recognise it?
A Plants wilt and collapse, as if they are short of water, even though the soil is moist. Foliage turns yellow, flowers shrivel, roots fail to grow and the plants ultimately die. Stems break easily near ground level.
Q Could I mistake it for anything else?
A Wilting from lack of water may look similar, but should not produce yellowing and is generally reversible once the soil is watered.
Q How serious is it?
A Many plants will fail to establish and die if grown in soil with high levels of Pythium violae infection.
Q What is its life cycle?
A Pythium is not a true fungus, but behaves in a similar way, producing resistant spores that remain in the soil to infect new plants.
Q When do attacks occur?
A Pythium spores inhabit the soil, waiting for the appropriate plant species to infect. If the same plants are grown in the same area year after year, levels of infection build up to the point where plants are seriously damaged.
Q How do I control an attack?
A There is no chemical control for pansy sickness. Once attacked, plants are unlikely to survive and should be removed and disposed of. If only some plants succumb initially, move the others to a different part of the garden, where pansies or violas have not been grown recently, or put them into containers of fresh compost.
Q How do I prevent it in future?
A Avoid growing pansies or violas in the same ground year after year. If this is unavoidable, remove the soil to a depth of 30cm every few years and replace it with soil from another part of the garden.