Purple Spot (Stemphylium)

Purple spot is a significant disease of asparagus. Infections occurring during harvest reduce the marketability of the crop (figure 1). Severe summer infections result in the premature defoliation of the fern, which can reduce the following year's yields by up to 52%.

Identification
|Tan-to-brown sunken, elliptical lesions with purple edges appear on infected spears, stems and fern (figure 2). As the disease spreads the lesions expand and merge together killing the affected tissue and eventually causing wide-spread defoliation (figure 3). Small black spores (pseudothecia) may be visible in the centre of the lesion, particularly on the previous season's crop residue.

Initial infections commonly occur on the bottom 30 cm (12 inches) of the stem, moving upwards onto the fern as the season progresses.