Verticillium wilt – Verticillium alboatrum – found on all vegetable crops
Verticillium wilt is caused by the fungus Verticillium alboatrum. Quite often verticillium wilt is confused with fusarium wilt. The fungus attacks a wide range of vegetable crops that are used commercially. Verticillium wilt is more common in areas of the greenhouse that is not sterilized for instance the growth medium and floor.
Symptoms of Verticillium wilt
The older leaves start to yellow accompanied by a slight wilting of the tips of the shoots during the day. Older chlorotic leaves wither and drop off. In severe cases the crown of the plant loses all its leaves. Younger leaves look dull and tend to curl up at the margins. All the branches are affected in the initial stages unlike bacterial wilt where one half of the plant can initially be affected. Plants can live for quite a while and it is not uncommon that they live throughout the production season, however, they stay somewhat stunted. If the plants live to a late age the leaves near the tip of the plant remain alive and the rest fall of.
The base of the stem, when cut lengthwise, shows a discolouration of the woody tissue. This symptom is also found when a plant is infected with fusarium wilt but the difference is that with verticillium the discolouration is slightly darker. Note that Verticillium wilt is found in the lower part of the plant stem. The stem itself does not decay and fruits are not spotted.
The fungus enters the plant through its roots and invades the xylem tissue of the stem. The ideal temperature for infection is between 21°C and 24°C. Temperatures higher than 24°C retard the development of verticillium but favours the development of fusarium.
Controlling Verticillium wilt
- One of the best measures to prevent infection from verticillium wilt is steam. Ensure that seedling medium is sterilized with either steam or other medium.
- Ensure that seedlings bought from a reputable nursery.