Squash (Cucurbita spp.)-Gummy Stem Blight (Black Rot)

Cause A fungus, Didymella bryoniae (asexual: Phoma cucurbitacearum), which overwinters on crop refuse and attacks numerous other cucurbits. The fungus will not survive in soil without cucurbit refuse or other cucurbit hosts. A small wound on the fruit, such as a fingernail scratch, is sufficient for disease development. The fungus will not grow below 50°F and can attack all parts of the plant.

Symptoms On leaves, brown to black circular spots generally associated with the leaf margins progress toward the center of the leaf. Stem infections will girdle the plant. On fruit, the fungus causes circular water-soaked spots. Regardless of where the lesion occurs, a gummy exudate is usually in the spot's center. Later the spot becomes covered with white mycelium and tiny black fungal fruiting structures (pycnidia and perithecia). The fungus causes a dry rot of the squash flesh.

Cultural control

  • Rotating out of cucurbits at least 2 years is the best control.
  • Use plastic mulch to prevent infecting fruit that rests on mulch.
  • Store only perfectly healthy fruit.
  • After harvest, cure squash 2 weeks at 75°F to 85°F.
  • Store squash slightly below 50°F if possible.
  • Avoid overhead irrigation when possible.

Chemical control

  • Carboxamide (Group 7) formulations are registered for use. 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. Preharvest interval is 0 days. 12-hr reentry.
    • Fontelis at 12 to 16 fl oz/A on 7- to 14-day intervals. Preharvest interval is 1 day. 12-hr reentry.
  • Chlorothalonil formulations (Group M5) are labeled.
    • Bonide Fung-onil (Group M5) is available for home gardens. H
    • Bravo Ultrex (Group M5) at 1.8 to 2.7 lb/A. May apply through sprinklers. 12-hr reentry.
    • Echo 720 (Group M5) at 2 to 3 pints/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
  • Copper products (Group M1) are not recommended as stand-alone materials.
    • Badge SC at 0.5 to 2.5 pints/A on 5- to 7-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
    • Cuprofix Ultra 40 Disperss at 1.25 to 2 lb/A on 5- to 7-day intervals. 48-hr reentry.
    • Kocide 2000 at 1 to 2.25 lb/A or Kocide 3000 at 0.5 to 1.25 lb/A on 5- to 7-day intervals. 48-hr reentry. O
    • Previsto at 0.75 to 2 quarts/A on 5- to 7-day intervals. 48-hr reentry. O
  • LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
  • Omega 500F (Group 29) at 0.75 to 1.5 pints/A on a 7- to 10-day interval. Applications should be directed to provide coverage of the lower stem area. Preharvest interval is 7 days. 12-hr reentry.
  • Orius 3.6F (Group 3) at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
  • OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O
  • Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 7- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Cabrio EG at 12 to 16 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Evito 480 SC at 3.0 to 5.7 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
    • Quadris Flowable at 11 to 15.5 fl oz/A on 10- to 14-day intervals. Do not apply within 1 day of harvest. 4-hr reentry.
  • Topsin M 70 WP at 0.5 lb/A on 7- to 14-day intervals. May be applied through sprinkler irrigation lines according to label directions. 12-hr reentry.
  • Premixes of fungicides are available and offer ease for fungicide resistance management. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action; for other fungicide groups apply no more than two (2) sequential applications alternating with another fungicide with a different mode of action.
    • Aprovia Top (Group 7 + 3) at 10.5 to 13.5 fl oz/A on 7 to 14-day intervals. May be applied the day of harvest. 12-hr reentry.
    • Dexter Max (Group M3 + 11) at 2.1 to 3.2 lb/A on 7- to 10-day intervals. Preharvest interval is 5 days. 24-hr reentry.
    • Dexter Xcel (Group M3 + 11 + 3) at 72 fl oz/A on 7- to 10-day intervals. Preharvest interval is 7 days. 24-hr reentry.
    • Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.
    • ManKocide (Group M1 + M3) at 2 to 3 lb/A on 7- to 10- day intervals. Under moderate to severe disease pressure use the higher rate on 5- to 7-day intervals. Do not apply within 5 days of harvest. 48-hr reentry.
    • Merivon Xemium (Group 7 + 11) at 5.5 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Miravis Prime (Group 7 + 12) at 9.2 to 11.4 fl oz/A on 7- to 14- day intervals. Preharvest interval is 1 day. 12-hr reentry.
    • Orondis Opti (Group M5 + 49) at 1.75 to 2.5 pints/A on 7- to 14-day intervals. Do not apply more than two (2) sequential applications. May be applied the day of harvest. 12-hr reentry.
    • Pristine (Group 7 + 11) at 12.5 to 18.5 oz/A. Preharvest interval is 0 days. 12-hr reentry.
    • Quadris Opti (Group 11 + M5) at 3.2 pints/A or Quadris Top (Group 11 + 3) at 10 to 14 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
    • Switch 62.5WG (Group 12 + 9) at 11 to 14 oz/A on 7-day intervals. Do not apply within 1 day of harvest. 12-hr reentry.

Biological control

  • Serenade ASO (Group BM02) at 2 to 4 quarts/A on 7- to 10-day intervals. Applications can be made up to and the day of harvest. 4-hr reentry. O