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Colletotrichum falcatum Went, 1893 (sexual stage Glomerella tucumanensis (Speg.) Arx & E. Müll.) · formerly or also: Glomerella tucumanensis, Physalospora tucumanensis
Red rot is the most destructive disease of sugarcane in South Asia and a serious one in other tropical cane regions. The fungus rots the inside of the stalk, turning it red with white cross-bands and giving it a sour, alcoholic smell; leaves dry from the top and whole clumps die. It spreads mainly through infected planting setts, and new pathogen strains repeatedly break down popular resistant varieties.
Red rot of sugarcane is caused by Colletotrichum falcatum Went, 1893 (sexual stage Glomerella tucumanensis (Speg.) Arx & E. Müll.), a fungus (ascomycete) (order Glomerellales, family Glomerellaceae).
Older or alternative scientific names: Glomerella tucumanensis, Physalospora tucumanensis.
Present in most sugarcane-growing countries. It is most damaging in South Asia, where epidemics have repeatedly forced the replacement of widely grown varieties, and is also important in parts of Southeast Asia, East Asia, the Americas, Africa and Australia.
| Region | Status |
|---|---|
| South Asia | Widespread; recurrent epidemics |
| Southeast and East Asia | Present |
| Americas and the Caribbean | Present |
| Africa, Indian Ocean and Oceania | Present |
The fungus forms acervuli with dark bristles on leaf midrib lesions and on rind of infected stalks, producing sickle-shaped conidia that are spread by rain splash, irrigation water and wind-driven rain. It survives in infected setts, stubble and crop debris. Pathotypes differ in virulence on varieties.
| Crop stage | What you see |
|---|---|
| Leaves (any stage) | Elongated, reddish lesions with dark margins on the midrib of leaves, later with straw-coloured centres and black dots. |
| Stalk elongation to maturity | The third or fourth leaf from the top yellows and dries along the margins, followed by drying of the whole crown; the stalk shrivels. |
| Inside the stalk | When split lengthwise, the internal tissue is red with white patches running across it (cross-bands), and smells sour or alcoholic; later the pith becomes hollow and dark. |
| Setts after planting | Infected setts rot and fail to germinate, leaving gaps. |
Infected setts are the main source: buds either fail or produce infected shoots. Spores from leaf and stalk lesions are carried by rain and floodwater to other plants and enter through nodes, root primordia and borer or other wounds. The fungus also survives in stubble and debris and infects ratoons.
| Stage | Duration | Notes |
|---|---|---|
| Infected setts and debris | Between crops | Main primary inoculum. |
| Infection of stalks and leaves | During rain and flooding | Through nodes and wounds. |
| Internal rot | Weeks to months | Symptoms obvious after the rains. |
| Sporulation | On lesions | Spread by water. |
Disease is favoured by warm, humid weather and waterlogging during the monsoon and post-monsoon period; temperatures of about 25-30 °C with high humidity speed it up.
One main crop cycle with secondary spread during wet periods.
Planting setts from infected fields, waterlogging and flooding that spread spores, continuous monoculture of one susceptible variety, ratooning infected crops, and borer damage.
There is no numeric economic threshold; any confirmed red rot in a seed plot means the cane should not be used for planting, and infected clumps should be removed promptly.
Affected cane loses weight and sucrose sharply; fields of susceptible varieties can be lost entirely, and regional epidemics have reduced cane and sugar output substantially in South Asia.
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 are used as sett treatments before planting where registered; they cannot cure standing infected cane. 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 | 1 | Methyl benzimidazole carbamates (MBC), sett treatment | Resistance risk. |
| FRAC | 3 | Demethylation inhibitors (DMI), sett treatment | Used in some programmes. |
| FRAC | 11 | Quinone outside inhibitors (QoI) | Used in some programmes. |
Sugarcane is the main host; the fungus can also infect sorghum and some wild 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.