Worldwide, although only of significance in tropical and sub-tropical regions.
Typically under field conditions leaves turn chlorotic, curl and twist resulting in an elongated neck and slender bulbs. Roots tend to be stunted and the plants may die. Small, white sunken lesions with dark, conidia-bearing structures may be present on leaves. When lesions are present, masses of pinkish-orange conidia may develop. Up to 100% crop loss can occur when environmental conditions favor this disease.
Conditions for Disease Development
This soilborne fungus has a wide host range and survives in infected debris and on alternate hosts. Propagules are spread by rain, wind, irrigation water and insects. High humidity and temperatures between 23-30°C (73-86°F) favor leaf infection.
Hybrids with resistance are available. Cultivation practices reduce soilborne inoculum and fungicide applications also provide effective control.