WILT (Drooping foliage)
Plants lose their freshness and foliage droops because of a lack of water. Wilt diseases involve bacteria or fungi interfering with the supply of water to the plant.
Because the symptoms do not occur necessarily where the infection is, it is a lot more difficult to treat a wilt disease than many other diseases.
Often infection occurs through wounds or root hairs below the soil, so spraying the foliage may not help at all.
These diseases are some of the most difficult fungal diseases to control.
Plants Affected: A wide range of plants including deciduous trees, vegetables, flowers and various other plants.
There are three main types of wilt diseases; all caused by either Fusarium, Verticillium and Ceratocystis fungi. There are other wilts as well (eg. on roses caused by a virus).
FUSARIUM WILTS
Spores are carried in soil. The fungus can spread from plant to plant in the soil to some extent growing short distances on dead organic material between roots of two different plants. They can affect most vegetables & flowers, and also banana, coffee and some shade trees. They are more likely to occur in warm conditions, and in greenhouses.
Losses are generally much higher only when both air and soil temperatures are high for an extended period.
On Tomatoes: Rapid wilting occurs on hot days, lower leaves yellow and wilt first, spreading upwards. Infected stems have brown streaks through the tissue when cut open. It needs warm weather 25 to 30 degrees C to develop.
On Carnations: Occasional branches turn yellow, and wilt, eventually spreading to the whole plant.
On Cucurbits: Growth rate is slow, occasional leaves wilt, spreads to whole plant.
(NB: Fusarium can cause other problems such as diseased gladioli corms, bulb rots etc).
Control:
Crop Rotation is important.
Remove infected plants and drench soil with benlate.
VERTICILIUM WILTS
Spores are carried in soil. They spread in a similar manner to Fusarium Wilts.
Plants Affected:
A wide range including many vegetables, flowers and fruit trees.
Attacks many different plants, but most serious problems are on vegetables, flowers and fruit (berries and trees). It also affects a range of ornamentals including roses, maples and elms.
Symptoms: Verticillium wilts commonly occur at lower temperatures than Fusarium, and the symptoms develop more slowly. Symptoms often appear on only part of the plant (eg. the outer parts lower parts or a few of the branches). When Verticillium infects seedlings, it usually causes a relatively fast death. When it affects older plants it can cause pale patches on foliage which develop into dead patches, foliage can drop, growth can be stunted. Wilting can gradually develop, culminating in death.
On Tomatoes: Lower leaves yellow, wilt and become dry. This progresses up the plant. Affected stems when cut open have brown markings inside.
On Chrysanthemums: Lower parts become purple or pink-green colour, then wilt and die.
(NB: This is a soil borne disease, will remain in the soil, and can affect other plants years later).
Control:
Crop rotation.
Improve drainage.
Drench soil with Benlate.
CERATOCYSTIS WILTS
Affect mainly trees. Spread by bark feeding beetles or poor propagation practices. The fungus grows in the outer layers of wood and inner layers of bark. Spores are not carried in the soil.
Want to Learn More?
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For more information on Courses on Pests & Diseases:
In Australia: www.acs.edu.au/Courses/General-Horticulture-courses.aspx
In the UK: www.acsedu.co.uk/Courses/General-Horticulture-Courses.aspx