Scouting for diseases: Pythium
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Pathogen: Pythium spp. (P. aphanidermatum,
P. debaryanum, P. ultimum, etc.).
Hosts include: Berberis, Calendula, Chrysanthemum,
Delphinium, Dianthus, Gaillardia, Gypsophila, Lathyrus, Lavandula,
Lilium, Lupinus, Pelar-gonium, Phlox, Salvia, Sempervivum and Viola.
Symptoms: Wilting, stunting, uneven plant growth, crown rot and
plant death. Roots are discolored. The cortex may slough off, leaving
the vascular cylinder.
Spread: Pythium spp. are soil-borne pathogens, so
movement of infested soil or plant material can spread disease. This
pathogen produces several types of spores, each with a slightly
different function. Sporangia can either germinate and infect plants
directly or produce many zoospores. Sporangia may be produced on both
above- and below- ground plant parts. Zoospores are motile spores, which
allow the fungus to spread in saturated soils or standing water. Each
zoospore can cause a new infection. Oospores are thick-walled spores,
which allow the fungus to survive on equipment or in soils for long
periods of time. Disease can be quickly spread through recirculated
irrigation water.
Management: Roots of incoming plant material should be checked
for root rot symptoms. Use media with good drainage and avoid
overwatering; do not use field soil in growing media for particularly
susceptible crops. Maintain good sanitation practices with equipment and
keep hose ends off the ground. Pythium spp. can develop resistance to mefenoxam, the active ingredient in several fungicides commonly used for Pythium spp. control. If Pythium spp. problems persist, diagnostic testing should be done to assess the sensitivity of the pathogen to mefenoxam.