DISEASE

NAME
Grey Mould
Botrytis cinerea, B. elliptica


Description
Grey Mold, Shoot Blight, Petal Blightis a fungus problem that generally forms water-soaked spots that rot and produces greyish sclerotia (fungal resting bodies) on the surface. They can be found throughout the year on dead tissue and on live material during under ideal climatic conditions. Damaged areas such as a tear in a leaf or an opening made by an insect are more likely to be infected.

Grey Mold on Begoniaspecies.
Image by B. Sonsie

Symptoms
The fungus attacks stems, leaves, flowers and fruit. Inrosesthe fungus is primarily attacks the flowers producing pink rings on the petals and buds that become brown and rotten. This may extend down the peduncle to the stems causing dieback.
In other plants oval yellowish to brown spots appear, then the centre turns greyish and dries out and in humid weather the spots spread, joining up and infecting the entire leaf. This infection may also occur on the stems, and flowers may form abnormally or brown off and die.

When lettuceis infected it starts at the base causing a soft brown rot that may extend up the stem killing the plant, and pears flowers become infected then spreading to the fruit. This develops a sunken brown area that is soft and eventually is covered in grey powdery spores.

      Botrytis Blight on Senecio cruentus

Botrytis Blight(Botrytis tulipae) infects leaves, flowers and stems with flecks of brown spots that merge to form light grey rotted areas that have brownish margin that may destroy stems. Affected areas are covered in a grey mould during humid conditions. The spores overwinter in dark brown sclerotia, which are found on the outer scales of the bulb or at the base of the stem in Tulipaspecies.

Grey Bulb Rot(Rhizoctonia tuliparum), which infects the bulbs of Tulipaspecies, attacking the base of the leaves and rotting the bulb. When bulbs emerge during spring in infected soil`s they soon die off. The greyish mold tends to be dry.

Source and Dispersal
The sclerotia (fungal resting bodies) are found on dead plant material or in the soil and remain viable for many years. The spores are dispersed by wind or splashing water.

Favoured Conditions
It prefers cool moist climate with morning dew.

Affected Plants
Grey Mold attacks a wide range of plants including roses, fruit trees, pelargonium, ferns, grapes and cyclamens. Heliotropium, Amaryllis,Liliumand Hippeastrumspecies are also infected.

Agavespecies are infected by two fungal Leaf Blights (Botrytis cinerea) and (Stagonospora gigantea) that severely damage the leaves particular during wet periods or from excessive watering.

Cactus species are infected by soft rot or Grey Mould (Botrytis cinerea). Stems and pads turn are greyish with the upper surface, rotting then collapsing. The dieing tissue becomes slimy and is covered with grey mould that develops black sclerotia, which propagates the disease. It is more prevalent under warm humid conditions and control methods include removing infected parts and destroying them. In glasshouse situations ventilation should be improved and watering should be restricted to create a drier atmosphere.

Cereusspecies and other cacti are infected by Grey Mold causing the segments to become discoloured and as the rot progresses it tissue becomes slimy and collapses. Black sclerotia forms on the affected areas that are covered in grey mold during humid conditions.

Cupheaspecies are infected by this blight.

Orchidssuch as Cattleya, Cymbidium, Cypripedium, Dendrobium, Epidendrum, Oncidium, Paphiopedilum, Phalaenopsis and Zygopetalumspecies are infected by Grey Moldor Petal Spot (Botrytis cinerea). Petal and flower stalks form small brown spots.

Paeoniaspecies are infected by Botrytis Blight (Botrytis paeoniae) causing the leaves and flowers to form a grey mold then suddenly collapse and die.

Pseudotsuga menziesii Douglas Firis infected by Leaf and Twig Blight(Botrytis cinerea). This is a serious problem in wet conditions and is difficult to control.

Ribesspecies are attacked by Cain Blight (Botryosphaeria dothidea). The infection causes the cains to become blighted and wilt. To control remove damaged wood and destroy.

Non-chemical Control
Remove and destroy infected plants or fallen leaves. When planting, space as to allow good air movement to reduce humidity. Bulbs that are infected should be discarded and take care that bulb scales are removed from the soil to prevent further infection. Cactus and succulents that are infected should have the damaged areas cut out, or discard the entire plant. Under glasshouse conditions improve the ventilation and reduce watering to create a drier atmosphere.

Chemical Control
Under humid conditions spray regularly using a suitable fungicide such as thiram, mancozeb, dichloran and chlorothalonil.
Note
Always read the label for registration details and direction of use prior to application of any chemicals.