Verticillium wilt is a soil-borne fungal disease of many fruit, vegetables and ornamental plants that enters the plant through the roots. Infection with this fungus causes dieback and the leaves to wilt.
What is verticillium wilt?
Verticillium wilt is caused by the soil-borne fungi Verticillium dahliae and V. albo-atrum. Both infect a very wide range of garden plants through the roots and then grow upwards in the water-conducting tissues, causing wilting of the upper parts due to water stress. Wilting is mostly seen from spring until autumn.
Plants most often affected include Chrysanthemum, carnation, aubergine, potato, tomato, cucurbits and strawberries. Woody plants are also affected, including Acer, Cotinus, Rhus, Berberis, Catalpa, Cercis and Rosa, but the full host range is very wide indeed. Conifers are not affected.
The most commonly affected plants recorded by the RHS Pathology Laboratory are Acer, Cotinus, Catalpa and strawberries.
You may see the following symptoms:
- Yellowing and shrivelling of lower leaves
- Some or all of the plant suddenly wilts, especially in hot weather. Plants may recover in cooler or wetter conditions
- Brown or black streaks in the tissue under the bark. These are visible as a circle of brown marks, if the stem is cut across transversely. In woody plants the marks are in the outer (most recent) growth ring, although older infections that were not fatal may have left similar marks in older, inner growth rings
- Branch dieback is a common symptom in trees and shrubs. Sometimes only part of the plant may wilt and dead branches may indicate infections which occurred in previous years
In woody plants verticillium wilt shows as brown or black streaks in the tissue under the bark. These are visible as a circle of brown marks if the stem is cut across transversely.
The fungus can be spread in contaminated soil, so if the disease is suspected, be careful not to spread soil from around the affected plants on tools or muddy boots.
Weed control is important, because some weeds are hosts and some may not show any visible signs of infection.
Where the disease is confirmed, taking care not to spread potentially infected soil around, remove the infected plant with as much root system as possible and destroy. Consider grassing over the area for at least fifteen years, or plant a resistant replacement.
Heavy watering and application of ammonium-based fertilisers (not nitrates) may stimulate the production of new conducting tissue in woody plants and help them recover, but this does not guarantee that re-infection will not occur in future years. To do this, apply a nitrogenous fertiliser to the root spread at 50g per sq m (2oz per sq yd) for urea or 25g per sq m (1oz per sq yd) for sulphate of ammonia once or twice during the remainder of the growing season.
Avoid replanting with the plants listed above as they are susceptible, especially Acer. Resistant plants include: Betula, Cercidiphyllum, Crataegus, Fagus, Gleditsia, Liquidambar, Morus, Platanus, Salix. Conifers are effectively immune.
See the download for a more complete list of susceptible and resistant plants.
Verticillium wilt – resistant and susceptible plants (Adobe Acrobat pdf)
There are no chemicals available to treat verticillium wilt.
Verticillium dahliae is more common in woody plants and V. albo-atrum in herbaceous plants, but their biology is very similar.
The fungi reside in the soil for many years in the form of microscopic, resilient, resting structures (micro-sclerotia in V. dahliae, resting mycelium in V. albo-atrum). These germinate and penetrate into the roots of susceptible hosts, where they grow into the water conducting system (xylem). Wilting develops due to a combination of physical blockage of the xylem vessels as a result of fungal growth and the fungus also produces toxins that are carried upwards in the water stream. The plant often blocks off its own xylem vessels with gums in a reaction to the toxins – this results in the brown streaks visible in the growth rings of infected plants. The fungus forms fresh resting structures in dead plant material.
In woody plants, the most active water conduction is in the most recently formed, outermost, growth ring and this is the one where the fungus spreads most actively.
Common name Verticillium wilt
Scientific name Verticillium dahliae and V. albo-atrum
Plants affected Many fruit, vegetables and ornamental plants
Main symptoms Yellowing leaves, wilting and dieback
Caused by Fungus
Timing Throughout the year, but may occur suddenly during hot weather