Violet root rot (Helicobasidium purpureum)
This fungal root infection (also known Rhizoctinia spp.
) is probably the most serious disease of asparagus but also affects a wide range of other crops. It spreads slowly from plant to plant via its mycelium
(mat of filaments). It can survive for years in the soil as irregular black lumps known as sclerotia
. It can also survive in a range of weed species, including bindweed, dandelion, dock, shepher's purse and nettle. It tends to affect older plants more severely and is more serious in warmer conditions. Its affects are not usually visible until later in the summer. Affected root crops cannot be stored but may still be edible once peeled as the fungus does not penetrate far.
- Slowly spreading patches of crop which yellow, wilt and may die
- Soil clings to the surface of root crops when lifted - they develop a leathery skin texture
- Only when you lift the root might you see the fine violet/purple mat of threads which gives this disease its name
- Roots may also develop a brownish rot as secondary infections enter the wounds created by the fungus
Prevention & control
- Carefully lift and burn all affected plants taking care not to drop infected soil or plant material on surrounding soil
- It may also be worth destroying apparently healthy surrrounding plants as these may be infected but symptomless
- As the mycelium spreads near the surface of the soil, a barrier (e.g polythene) dug a foot or so into the soil, should prevent spread by this method
- Plant only crops which are not affected by the disease for at least 4 years on the same bed
- Keep host weed species under control