DISEASE

NAME
Sclerotinia Rot, Crown Rot
Sclerotinia species


Description
A fungal problem that attacks plant parts causing them to collapse and rot, including flower, leaf and stems.

Symptoms
This fungus attacks all the above ground parts of the plant but commonly infects the stem at the base, where it forms a soft, light brown watery rot that spreads rapidly. Under humid conditions the rotted areas forms white fluffy mycelium on which black sclerotia up to 10mm long develop. These sclerotia also form within the stem in affected areas. When leaves are infected the tissue may brown and dry out, especially during arid conditions. The resulting affect of infection is the death of the plant.


Image by B. Sonsie

Crown Rot(Sclerotium delphinii) causes leaves to turn yellow then become dry, and blossoms to wilt eventually killing the entire plant. It is found on Scilla, Viola and Delphiniumspecies.

Flower Blight(Sclerotinia camelliae) infects flowers either by attacking the top of the petals forming brown specks or at the base of the flower where the petals turn brown then fall with out any sign of rot. The fungus develops on the fallen petals where microconidia are produced under moist conditions and eventually sclerotia appear. This form of the fungus can overwinter either above or below soil level until favourable conditions occur, then the spores are released and dispersed by wind.

Source and Dispersal
Sclerotia are found in the soil or on other infected plants and released spores are dispersed by wind.

Favoured Conditions
Prefers cool moist conditions with temperatures from 10ş to 25şC and is more common from autumn to spring when it is wet.
     
Affected Plants
A wide range of plants can be infected included French beans, peas, celery, cabbage, cauliflowers, carrot, parsnip, dahlia stocks, primula and many weeds.

Actinotus, Dampiera, Westringa species andHelichrysum bracteatum are infected by the Crown Rot (Sclerotinia rolfsii). Basial rot of the plant with cottony fungal growth and is associated with root congestion. Certain species of orchid may also be attacked.

Alliumspecies are infected by the White rot(Sclerotium cepivorum) which is a major fungal disease of plants.
The bulb rot and are covered in mycelial which develop small black sclerotia (fruiting bodies) and infected plants may fail to produce flowering stem with the leaves become covered in a white mould, turning yellow then dieing off. It is commonly transmitted by infected seedlings and diseased plants should be burnt. Avoid re-planting Alliumspecies in the infected soil where the spores overwinter. Soil may be infected for several years.

Antirrhinum, Aquilegia, LobulariaandMathiola species are attacked by the Stem Rot(Sclerotinia sclerotiorum ) which infects the stigma travelling downwards through the flower into the stem where water soaked areas appear causing it to collapse. The flowers become pale and the entire plant may collapse. On inspection flat sclerotia may be seen in the stem.

Camelliaspecies may be infected by Flower Blight(Sclerotinia camelliae) which causes blooms to fall and Stem Rot(Sclerotinia sclerotiorum).

Hyacinthusspecies can be infected by the fungus Black Slime(Sclerotinia bulborum) that causes the leaves to turn yellow then fall and bulbs to disintegrate.

Irisspecies are infected by the fungus Rhizome Rot(Botryotinia convoluta) that infects the rhizomes and forms black sclerotia, and is normally found on dieing plants during spring.

Turf Grassin warm climates is susceptible to Rolf`s Disease (Sclerotinia rolfsii). The fungus infects the turf causing isolated dead patches up to 450mm across from spring to summer. As it progresses the dead patches increase in size and the white cotton-like mycelium can be seen in the underlying soil. It is not regarded as a major problem, with minor attacks on Cynodon dactylon(Couch) andZoysiaspecies.

Non-chemical Control
Initially remove and destroy any infected plants, when replanting, avoid using susceptible crops for 3 years. Space the plants to reduce the humidity and airflow and cultivate the soil to increase the drainage. Remove weed growth and leaf or flower litter from around the base of the plants to reduce the development of spores
Turf Grass culture such as aerating soil and maintaining a neutral pH helps prevent infection of Rolf`s Disease.

Chemical Control
No suitable fungicides available, though drenching or spraying the soil with the fungicide dichloran helps control it.