Just What We Don't Need
Paul Banks, Technician, Ontario Agricultural College
Jul 20th, 2004
In 2004, Norm Myers, the Oceana County Extension Director, reported that Phytophthora crown and spear rot had been found in Michigan. This fungus is known to cause serious losses in California, but it was not thought to be a problem for asparagus growers in the north-east U.S. or in Canada.
Phytophthora causes the most damage when soils are cool and wet. The fungus produces swimming spores that need a film of water in order to spread to roots, spears or stems. If the soil turns hot and dry, resting spores are produced that remain viable in the soil for years. Cool, wet weather is frequent in the spring and fall in California, and Phytophthora is prevalent. This year, some areas of Michigan received 15 inches of rain in May and June providing the right sort of conditions for infection. This suggests that Phytophthora crown and root rot has been present in asparagus fields for years causing little damage most of the time but capable of causing losses when conditions are right.
Phytophthora usually infects spears near the soil line causing translucent, sunken lesions that expand rapidly. If the humidity is low, the lesions will dry out causing spears to crook. If humidity is high, secondary bacterial infections cause spears to break down into a slimy mess. If the water used for hydro cooling becomes contaminated, then spears will also break down in storage or when shipped to market.
It is too early to say how many fields in Michigan have been contaminated inadvertently with Phytophthora, or how often crown death has been blamed on Fusarium when, in fact, the culprit was Phytophthora. It could happen just as easily this side of the border. In fact, plant pathologists in Quebec reported in 2003 that wilt in a commercial asparagus field in the Saguenay-Lac St. Jean region was due to Phytophthora. It was the first report of Phytophthora crown and spear rot on asparagus in Canada.