Squash (Cucurbita spp.)-Alternaria Leaf Blight

Cause Alternaria cucumerina, a fungus that overwinters primarily in infected plant debris.

Symptoms First, small brown spots are on the oldest leaves, which turn brown to black as the disease progresses. Spots on the upper leaf surface take on a target-spot or ringed look. Fruit decay is dry and tough on the surface but moist and spongy inside the squash.

Cultural control

  • Rotate out of cucurbits 2 to 3 years before planting squash.
  • Minimize the time leaves are wet by irrigating overhead briefly and only during the day. Drip irrigation is even better.

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 is available for home gardens. H
    • Bravo Ultrex at 1.8 to 2.7 lb/A in enough water to cover plants. May apply through sprinkler systems. 12-hr reentry.
    • Echo 720 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.
    • Champ WG at 1.5 to 2 lb/A on 5- to 7-day intervals. 48-hr reentry. O
    • Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
    • 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
    • Liqui-Cop at 2 to 3 teaspoons/gal water. H
    • Previsto at 0.75 to 2 quarts/A on 5- to 7-day intervals. 48-hr reentry. O
  • JMS Stylet Oil at 3 to 6 quarts/100 gal water. Effectiveness is unknown in the Pacific Northwest when used alone. Do not spray if temperature is below 50°F or above 90°F or when plants are wet or under heat or moisture stress. 4-hr reentry. O
  • Mettle 125 ME (Group 3) at 8 fl oz/A on 7- to 10-day intervals. Application can be made the day of harvest. 12-hr reentry.
  • Omega 500F (Group 29) at 0.75 to 1.5 pints/A on a 7- to 10-day interval. Preharvest interval is 7 days. 12-hr reentry.
  • 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. 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. Do not apply within 1 day of harvest. 4-hr reentry.
    • Reason 500 SC at 5.5 fl oz/A. Do not apply within 14 days of harvest. 12-hr reentry.
  • Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
  • Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O
  • 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. Some cantaloupe varieties are sensitive to Dexter Max. 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. Some cantaloupe varieties are sensitive to Dexter Xcel. Preharvest interval is 7 days. 24-hr reentry.
    • Gavel 75 DF (Group 22 + M3) at 1.5 to 2.0 lb/A on 7- to 10-day intervals. Preharvest interval is 5 days. 48-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 4 to 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. May be applied the day of harvest. 12-hr reentry.
    • Pristine (Group 7 + 11) at 12.5 to 18.5 oz/A on 7- to 14-day intervals. 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 12 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- to 10-day intervals. Do not apply within 1 day of harvest. 12-hr reentry.

Biological control

  • Actinovate AG at 3 to 12 oz/A as a foliar spray on 7- to 14-day intervals. 1-hr reentry. O
  • Actinovate Lawn & Garden at 1/2 to 1 teaspoon/gal water. H O