Squash (Cucurbita spp.)-Sclerotinia Stem Rot

Cause The fungus, Sclerotinia sclerotiorum, has been observed frequently in Oregon, particularly on zucchini and kubocha squash. This fungus overwinters in soil as sclerotia or on old infected plant material. The greatest losses are in pumpkins or squash piled in the open, or in storage, following preharvest infection. In storage, the disease is called watery soft rot.

Symptoms Plants wilt, and a discoloration of the vascular tissues may be noticed. Affected tissue near the soil line becomes water soaked as disease progresses. A profuse, cottony white growth may be on rapidly spreading lesions. Black fruiting bodies (sclerotia) are produced later in the lesions.

Cultural control

  • Avoid overhead irrigation or excessive watering through a drip line.
  • Deeply plow under plant debris soon after harvest if possible.
  • Space plants and rows to promote fast drying.
  • Rotate crops-grasses and cereals do not appear to be susceptible.

Chemical control

  • Carboxamide (Group 7) formulations are registered for use in squash. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action.
    • Endura at 6.5 oz/A on 7- to 14-day intervals is labeled for other diseases in squash. Preharvest interval is 0 days. 12-hr reentry.
    • Fontelis at 16 fl oz/A on 7- to 14-day intervals. Preharvest interval is 1 day. 12-hr reentry.
  • Topsin M WSB (Group 1) at 0.5 lb/A on 7- to 14-day intervals is labeled for gummy stem blight and will give good control of Sclerotinia. May be applied through sprinkler irrigation lines according to label directions. 24-hr reentry.