Botrytis rot or grey mould fungus – symptoms and control
Botrytis rot (Botrytis cinerea)
Botrytis rot (Botrytis cinerea), also known as grey mould, is caused by the fungus Botrytis cinerea, and has become on the most serious diseases of tomato foliage and fruit. The fungus becomes established on dead leaves or stems at the base of the plant. A heavy grey growth of the fungus occurs these and numerous spores soon appear on the material. Botrytis rot spores are easily spread by air movement. The fungus can manifest itself as damping-off of young seedlings such as in lettuce. See section about damping-off.
Botrytis rot Symptoms
On fruit it appears as soft rot. Where the skin ruptures, the characteristic fungal growth is visible with masses grey spores. Leaves show typical light-tan or grey spots. The infected areas become covered by a growth of the fungus and the leaf collapses and withers. As this happens the fungus progresses to the stem and produces distinctive elliptical cankers. These extend some distance up the stem and are tan with concentric markings. Often the surfaces overgrown by fungi that only affect dead tissues and it then becomes black rather than tan.
The fruits show water soaked and softened tissue. The water soaked spots are irregular in shape and are approximately 25mm in diameter. The fungus that develops on the surface of the fruit shows a dark grey growth. If no control is applied and fungus is let to develop to an advance stage the fruit is destroyed by a watery soft rot.
Infection occurs through leaf injury caused by insect wounds or physical damage. Damage caused by other fungi and parasites are also common points of entry. Fruits may also be infected through the stem, scars, growth cracks, abrasions from blowing sand or other breaks in the epidermis. The disease is most common during cool and wet weather conditions.
Botrytis rot control
- Identify environmental conditions which is favourable for disease development.
- Follow a spraying program with registered chemicals.
- Acidic soils has a negative influence on calcium uptake in the plant. Calcium is an integral part of the cell wall. Insufficient calcium uptake will directly be responsible for a structurally inferior plant and will predispose the plant to infection by this fungus.