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

  • Aprovia Top (Group 7 + 3) at 10.5 to 13.5 fl oz/A on 7 to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. 12-hr reentry.
  • Bonide Fung-onil is available for home gardens. H
  • Bravo Ultrex (Group M5) at 1.8 to 2.7 lb/A in enough water to cover plants. May apply through sprinkler systems. 12-hr reentry.
  • 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.
  • Copper products are not recommended as stand-alone materials.
    • Champ WG at 1.5 to 2 lb/A on 5- to 7-day intervals. 48-hr reentry. H 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 40D 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.
    • Liqui-Cop at 2 to 3 teaspoons/gal water. H
  • Echo 720 (Group M5) at 2 to 3 pints/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
  • Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals with no more than (2) sequential applications. Preharvest interval is 7 days. 12-hr reentry.
  • 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
  • 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.
  • 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.
  • 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.
    • Pristine at 12.5 to 18.5 oz/A. Preharvest interval is 0 days. 12-hr reentry.
    • Quadris Flowable at 11 to 15.5 fl oz/A. Do not apply within 1 day of harvest. 4-hr reentry.
    • Quadris Opti at 3.2 pints/A or Quadris Top at 12 to 14 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
    • Reason 500 SC at 5.5 fl oz/A. Do not apply within 14 days of harvest. 12-hr reentry.
  • Trilogy at 0.5% to 1%. 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

Biological control

  • Actinovate AG at 3 to 12 oz/A as a foliar spray on 7- to 14-day intervals. 1-hr reentry. O
  • 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