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. (Sclerotia of sclerotinia collar rot caused by S. minor are smaller and more angular).
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. Infected pods are cream and may contain mouldy seeds.
In Lettuce the leaves the leaves wilt and the plant becomes limp.

Species Affected:

Crop such as Brassicas, Beans, Cabbage, Capeweed, Cauliflower, Canola, Carrots, Celery, Chickpeas, Dahlia, legumes, Lentils, Lettuce, Lupins, Peas, Soybeans, Sunflower, Tomato and Potato are very susceptible.
Weeds such as Capeweed, Shepherds Purse and Wild Radish will host it.
Over 400 species can act as hosts.
Cereals, grasses, Beetroot, Onion, Spinach, and Sweet Corn are resistant.
More than 400 species will host it.

Biology:

Favoured by cool, wet conditions and cultivation. Tolerates a wide temperature range. 10-14 days of wet soil conditions in mid to late winter, with
temperatures of 1°C to 15°C favouring development of apothecia (fruiting bodies). Temperatures of 15°C-25°C at petal fall allows the disease to spread
from infected petals to other parts of the plant. Dry conditions during flowering and petal fall can limit the disease
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 (at least 6) years in the soil. When buried at 3 cm they have survived for up to ten years.
Sclerotes can germinate from 5 cm deep (but usually only in the top 3 cm) and produce up to 15 apothecia (or tiny golf tee shaped mushrooms) that release millions of spores.
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.
Sclerotes require high humidity with temperatures of 10-200C to germinate and produce apothecia. In moist conditions they will germinate after 40 days at 10/220C and down to 23 days in some conditions. None germinated under night/day temperatures of 16/290C (Beard, Hills and Khangura pers com.)
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. Humid moist weather at flowering leads to petal infections in canola. These petals drop down into the canopy after 30% bloom and lodge in the leaf axils or leaves. The fungus invades the leaves and branches and progresses to the stems.
Basal stem infection can occasionally occur directly from the soil and in these cases the lesions can be seen before flowering.
Yield losses are associated with main stem infections. Foliar fungicide applications aim to prevent main stem infections and reduce potential yield loss. Prothioconazole + tebuconazole (e.g. Prosaro®) provide about 3 weeks protection and bixafen + prothioconazole(e.g. Aviator®) provides slightly longer protection.

Origin and History:

Distribution:

Significance:

Very damaging to Brussels Sprouts and Cabbage heads.
In Canola yield losses up to 30% have been recorded in Australia.

Management and Control:

Increase time between successive susceptible crops to 3-4(5) years. Intersperse with resistant species like cereals, grasses or Faba Beans and avoid other legumes (especially Lupins), Canola, Capeweed, Shepherds Purse, Radish, Turnip or Mustard infested areas
Control weeds that may act as alternate hosts.
Destroy crop residues soon after harvest.
Use clean seed that has no sclerotia contamination.
Avoid sowing early maturing canola in April to reduce the risk of flowering when apothecia are germinating in June/July.
Plant susceptible crops more than 500 m from infected crop stubbles or paddocks with a history of infection within the last 4 years.
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 (Valarini et al., 1996).
Burning has variable results. High temperatures can kill sclerotes whereas lower temperatures may induce earlier germination making control more difficult.

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 (Hind-Lanoiselet and Lewington, 2004). Burning has variable results. High temperatures can kill sclerotes whereas lower temperatures may induce earlier germination making control more difficult.
Burying sclerotia laden top soil to a depth of 80 mm appears to be sufficient for Canola (Hind-Lanoiselet and Lewington, 2004).
Monitor crop for apothecia (little mushrooms) early in the season and cotton wool symptoms on stems and branches later in the season.
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 (Hind-Lanoiselet and Lewington, 2004). 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 (Hind-Lanoiselet and Lewington, 2004).
Apply fungicides at 30% flowering or at 50% flowering for late epidemics. Applications after 50% flowering are rarely economic. In heavily infested areas a spray at 10% flowering followed by a second spray at 50% flowering provided the best yields (Khangura and Jayasena).
Iprodione, procymidone, tebuconazole and prothioconazole are often used in broadacre crops. These are not curative and therefore most effective before the disease is evident.
Australian Canola varieties have little resistance at present (Hind-Lanoiselet and Lewington, 2004).
Row spacing and canola density had little effect on disease in WA trials.
A model to help predict Sclerotinia effects in canola is available from the Department of Primary Industries and Regional Development in Western Australia.

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

Sclerotinia is an occasional disease of Lupins.
Lesions occur on the stems, branches, flower spikes and pods.
Don't plant seed from crops with infected pods.
Don't sow Lupins for at least 3 years after a severe disease event.
There appears to be little difference in tolerance between lupin varieties.

Related and Similar Species:

Sclerotinia minor has sclerotia that are 1-2 mm long, oval to spherical and often clumped together.
Blackleg in canola may look similar but always has little black dots or microspores within the leasion.

References:

(Donald et al., 2002)

(Marcroft et al., 2002)

(McMaugh, 1985)

Acknowledgments:

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