ABSTRACT

Powdery mildew is probably the commonest disease of cereals, occurring in all areas where crops are grown. Disease symptoms can occur on all aerial plant parts, but are most frequently seen on leaves (33-37). Early disease symptoms consist of chlorotic flecks on plant tissue. A white, fluffy mildew pustule soon develops (38, 39), which produces masses of powdery spores. Older mildew pustules may assume a grey or brown tinge. The fungus infects only the outer epidermal plant layers and so pustules can be scraped off the leaves relatively easily. Occasionally, mild chlorosis can be seen in affected tissues, particularly at the beginning of natural leaf senescence, but the pathogen does not usually kill its host. Towards the end of the season, brown-black sexually produced spore cases (cleistothecia) may be found embedded in mildew pustules (40).