Sclerotinia stem rot
A cool-weather watery stem rot with white cottony mould outside and large hard black sclerotia inside the hollowed stem.
- Pathogen
- Fungus (Sclerotinia sclerotiorum)
- Spreads by
- Soil-borne sclerotia; air-borne spores
- Favoured by
- Cool, humid, wet weather at flowering
- Main risk
- Stems girdled and killed; lodging
Overview
Sclerotinia stem rot (white mould) is caused by the fungus Sclerotinia sclerotiorum, which attacks mustard and other oilseeds, sunflower, cole crops (cabbage, cauliflower), and many vegetables and pulses. It shows as a soft, watery, pale rot on the stem, branches or stalk — often starting where petals or dead flowers stick to the plant — that girdles the stem so the part above wilts, ripens prematurely and dies.
The diagnostic signs are a white, cottony fungal growth on and inside the affected stem, and — when you split the stem — large, hard, irregular black sclerotia (looking like rat droppings) inside the hollowed pith. These sclerotia fall into the soil and survive for many years, germinating in cool, humid weather to release spores that infect the crop, especially at flowering. Because the soil inoculum is so persistent, management leans on rotation, deep ploughing, canopy management and a protective fungicide at flowering.
How to identify it
- A soft, watery, pale rot on the stem, branch or stalk, often starting where petals or dead flowers lodge on the plant.
- A white, cottony fungal growth on and inside the affected stem in humid weather.
- Large, hard, irregular black sclerotia (like rat droppings) inside the hollowed, bleached stem when you split it.
- The stem girdled so the part above wilts, ripens prematurely, whitens and dies, and the plant may lodge.
What causes it and when
- The fungus Sclerotinia sclerotiorum, whose black sclerotia survive for many years in the soil.
- Sclerotia germinate in cool, humid, wet weather to release air-borne spores that infect the crop, especially at flowering.
- Favoured by dense canopies, cool humid conditions and shed petals/flowers that give the spores a food base.
- Worst in the flowering-to-podding stage of a lush crop in cool, moist weather.
Cultural & organic control
- Rotate with non-host crops (e.g. cereals) to run down the long-lived soil sclerotia.
- Deep-plough to bury sclerotia, use wider spacing and balanced nitrogen to open the canopy, and ensure good drainage.
- Rogue out and remove affected plants (with the sclerotia) before they shed into the soil.
- Apply a bio-agent (e.g. Trichoderma/Coniothyrium) to soil where recommended to attack the sclerotia.
Chemical control
- The key spray is protective, at flowering, when the crop is most vulnerable — a spray after the stem is rotted does not help.
- Use a CIB&RC-registered fungicide (e.g. carbendazim or other recommended products) at early flowering where the disease is expected.
- Cover the stems and lower canopy, not just the top, and observe the pre-harvest interval.
- Confirm the current product, dose and timing for your crop with your local KVK.
Prevent it coming back
- Rotate with non-hosts, deep-plough, and open the canopy with spacing and balanced nitrogen.
- Plan the protective flowering-stage spray in advance in fields with a history of the disease.
- Remove affected plants with their sclerotia and manage drainage to reduce the cool, wet conditions it needs.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My mustard/sunflower stems are rotting with white cottony growth and hard black lumps inside. What is it?
That watery stem rot with white cottony mould, and large hard black sclerotia (like rat droppings) inside the hollowed stem, is Sclerotinia stem rot. It strikes in cool, humid weather, usually infecting at flowering where petals lodge on the plant. The sclerotia survive for years in the soil, so control combines rotation, deep ploughing, an open canopy, and a protective fungicide at flowering.
What are the hard black lumps inside the rotten stem?
They are the sclerotia of Sclerotinia — large, hard, irregular black resting bodies that form inside the hollowed pith of an infected stem and look like rat droppings. They are how the fungus survives for many years in the soil after they fall from the stem. Seeing them confirms Sclerotinia and warns that the field is now carrying long-lived inoculum, so rotation and deep ploughing become important.
When should I spray for Sclerotinia?
At flowering — the protective window. Sclerotinia typically infects the crop at flowering, often through shed petals that stick to the plant, so a fungicide (e.g. carbendazim) applied at early flowering protects the crop, while a spray after the stems have rotted does nothing. In fields with a history of the disease, plan the flowering spray in advance and combine it with rotation and an open canopy. Confirm the product with your KVK.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.