Elaine Roddy, Vegetable Crops Specialist
Purple spot is a significant disease of asparagus. During wet, windy weather conditions, purple spots develop on the emerging spears. These purple spots do not impact either the flavour or texture of the spear. In fact, they typically disappear during cooking. Unfortunately the unsightly appearance drastically impacts the marketability of the crop.
Severe summer infections result in the premature defoliation of the fern, which can reduce the following year’s yields by up to 52%.
Tan-to-brown sunken, elliptical lesions with purple edges appear on infected spears, stems and fern. As the disease spreads the lesions expand and merge together killing the affected tissue and eventually causing wide-spread defoliation.
Purple spot is most prevalent during cool, wet conditions. It is often active during the late spring and again in the late-summer. Hot, dry conditions in July and August will slow the progression of this disease, however levels of infection can increase dramatically as the temperatures cool in early fall.
For more information, see the OMAFRA infosheet, Asparagus Diseases—Purple Spot (Stemphylium) at: http://www.omafra.gov.on.ca/english/crops/hort/asparagus-diseases-purple-spot.htm