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Claviceps africana Frederickson, Mantle & De Milliano, 1991 (with C. sorghi in South Asia) · formerly or also: Sphacelia sorghi (asexual stage)
Sorghum ergot infects unfertilised sorghum flowers and replaces the grain with fungal tissue that oozes sticky, sweet honeydew - hence 'sugary disease'. It is most dangerous in hybrid seed production, where male-sterile lines flower without their own pollen, and after cool nights that make pollen sterile. In the 1990s it spread from Africa and Asia to the Americas and Australia within a few years.
Sorghum ergot is caused by Claviceps africana Frederickson, Mantle & De Milliano, 1991 (with C. sorghi in South Asia), a fungus (ascomycete) (order Hypocreales, family Clavicipitaceae).
Older or alternative scientific names: Sphacelia sorghi (asexual stage).
Long known in Africa and South Asia. Claviceps africana spread to Brazil in 1995, Australia in 1996 and Mexico and the United States in 1997, and is now present in most sorghum regions.
| Region | Status |
|---|---|
| Africa | Native; widespread |
| South Asia | Present, with Claviceps sorghi |
| Americas | Introduced in the late 1990s; widespread |
| Oceania | Present in Australia since 1996 |
Infected florets produce honeydew containing conidia (macroconidia) that germinate on the surface to form secondary conidia carried by wind. Later, white to dark sclerotia (sphacelia) replace the grain; sclerotia of C. africana contain the alkaloid dihydroergosine, which is toxic to livestock.
| Crop stage | What you see |
|---|---|
| Flowering | Droplets of sticky, sweet, pinkish to brown honeydew oozing from infected florets a week or so after flowering. |
| Grain fill | Honeydew dripping onto leaves and soil, becoming white and crusty with secondary spores, and attracting insects; sooty moulds grow on it. |
| Maturity and harvest | White to cream or dark sclerotia instead of grain; sticky heads clog harvesters; contaminated grain is unfit for feed. |
Airborne secondary conidia land on stigmas of unfertilised flowers and infect the ovary. Once a flower is fertilised it becomes resistant, so anything that delays or prevents pollination increases infection. Spread within and between fields is by wind-borne spores from honeydew; the fungus survives on volunteer and wild sorghums and as sclerotia and contaminated seed. Long-distance spread of secondary conidia on wind explains how the disease crossed continents so quickly in the 1990s, once it had reached a new region on seed or by air.
| Stage | Duration | Notes |
|---|---|---|
| Infection of unfertilised florets | During flowering | Resistant once fertilised. |
| Honeydew production | About 7-10 days after infection | Sweet exudate with conidia. |
| Secondary conidia | Days | Wind-dispersed over long distances. |
| Sclerotia | Grain maturity | Contaminate grain and seed. |
Night temperatures below about 12-13 °C in the weeks before flowering reduce pollen viability and greatly increase ergot; humid, cool weather during flowering favours infection.
Several cycles while unfertilised florets are available.
Male-sterile seed-parent lines in hybrid seed production, cool nights before flowering, humid weather at flowering, poor synchrony between male and female flowering, and late tillers flowering after the main crop.
There is no numeric economic threshold; in seed production fields protection is applied from the start of flowering, and grain lots are judged against feed-safety limits for sclerotia and alkaloids set nationally.
Thresholds are local. They depend on crop price, control cost, variety and natural-enemy activity, so use the figure your local extension service publishes where one exists.
Seed production fields can lose most of their seed set; in grain crops losses are usually small but sticky heads hamper harvest, and sclerotia make grain unfit for livestock feed because of alkaloid toxicity. Infected hybrid seed lots are rejected or must be cleaned, and the sticky honeydew attracts insects and supports moulds that further lower quality.
Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.
Fungicides applied from the start of flowering protect seed production fields where registered. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.
| Scheme | Group | Mode of action | Notes |
|---|---|---|---|
| FRAC | 3 | Demethylation inhibitors (DMI) | Protects flowers in seed production. |
Grain and forage sorghum and wild sorghums; related Claviceps species attack pearl millet and other grasses.
How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:
Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.