Sclerotinia Rot

Sclerotinia sclerotiorum

Names:

Bean White Rot.
Brassica White Mould
Canola Sclerotinia Stem Rot
Capsicum Stem Rot
Carrot Sclerotinia Rot
Carrot Pink Rot
Celery Pink Rot
Clover Sclerotinia
Dahlia Stem Rot
Lettuce Drop
Potato White Mould.
Tomato Stem Rot

Description:

Soft, brown, rapidly spreading, wet rot with white, cottony, dense fungal growth on the surface of heads and stems. It sometimes has black, hard spore bodies (sclerotia) which may be formed inside the stems or on the surface.
Sclerotia of Sclerotinia sclerotiorum are 5-10 mm long, irregular shape and look like rat faeces.
Symptoms vary between species.
In Beans the infected pods look normal at harvest and develop the rot in storage.
In Canola a white fluffy growth appears on the stem which is greyish white or brownish white underneath the fluff or later in the season. Initially lesions may appear as brown patches on stems and pods. Plants may wilt, die and lodge above the infected area. Affected areas may prematurely ripen and individual plants may stand out as grey or bleached plants amongst green neighbours. Late in the season black irregularly shaped sclerotia from the size the size of a pin head (for S. minor) to a rat dropping (for S. sclerotiorum) form on and in the stem near the base. It is usually seen when there has been warm wet weather during flowering in spring.
In Lettuce the leaves the leaves wilt and the plant becomes limp.

Species Affected:

Brassicas, Beans, Cabbage, Capeweed, Cauliflower, Canola, Carrots, Celery, Dahlia, legumes, Lettuce, Lupins, Peas, Soybeans, Sunflower, Tomato and Potato are very susceptible.
Cereals, grasses, Beetroot, Onion, Spinach, and Sweet Corn are resistant.

Biology:

Favoured by cool (10-250C), wet conditions and cultivation. Tolerates a wide temperature range.
Most common in autumn and spring on moist soils.
Tends to initially attack old or decaying leaves and tissue or petals.
Sclerotia can survive for many years in the soil.
Often builds up on susceptible hosts such as Brassicas, legumes, Capeweed, Lettuce and Potato.
Spread by movement of soil containing spores.
It can produce wind dispersed spores.

Life Cycle:

On Canola.

Courtesy Canola Council.
Apothecia are small golden mushroom like bodies that produce wind dispersed spores (ascospores) that can be carried several kilometres.
In Australia, spores can germinate on dead or dying leaves as well as petals and then infect the Canola plant.
Basal stem infection can occasionally occur directly from the soil and in these cases the lesions can be seen before flowering.

Origin and History:

Distribution:

Significance:

Very damaging to Brussels Sprouts and Cabbage heads.
In Canola yield losses up to 24% have been recorded in Australia.

Management and Control:

Increase time between successive susceptible crops to 3-4 years. Intersperse with resistant species like cereals and grasses and avoid legumes (especially Lupins) and Capeweed.
Control weeds that may act as alternate hosts.
Destroy crop residues soon after harvest.
Use clean seed that has no sclerotia contamination.
Deeply cultivate with mouldboard plough to bury sclerotia laden soil 150 mm deep.
Avoid moving infected soil to cropping areas.
Maintain weed free conditions to reduce alternate hosts carrying the disease.
Space plants to reduce humidity.
Avoid watering during humid conditions.
Improve drainage.
Apply fungicides at the first sign of disease.
Lemon grass extracts reduce the disease (892).
Australian Canola varieties have little resistance at present (1299).

Canola

Avoid planting canola close to areas that had canola in the previous season.
Burning requires a hot fire with temperatures reaching 1210C which is often difficult to achieve after canola crops (1299).
Burying sclerotia laden top soil to a depth of 80 mm appears to be sufficient for Canola (1299).
A petal test is used overseas to determine the level of infection but this has not been reliable in Australian trials apart from determining maximum level of infection (1299). It is available from NSW Agriculture's Plant Health Diagnostic Service
Wet weather during flowering and low temperatures may lead to epidemics that may be worth controlling.
Applications of fungicides such as Rovral® or iprodione at the first sign of disease can be profitable in high yielding good crops that have heavy aerial infections. Fungicides are more effective on aerial rather than basal infections (1299).

Capsicums and Celery

Fumigate infected areas.

Carrots

Discard damaged Carrots
Store Carrots in cool, well-ventilated areas.

Lettuce

Destroy all infected crop residues.
Rotate with resistant crops.
Control alternate hosts in the crop and adjacent areas.
Apply fungicides at the first sign of disease.
Fumigate severely infested areas.

Lupins

Don't plant seed from crops with infected pods.
Don't sow Lupins for at least 3 years after a severe disease event.

Related and Similar Species:

Sclerotinia minor has sclerotia that are 1-2 mm long, oval to spherical and often clumped together.

References:

1292

1297

1291

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.