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Angular leaf spot

Quick facts

  • Angular leaf spot can infect all cucurbit crops.
  • Leaves develop small, angular, brown or straw-colored spots with a yellow halo. Leaf spots dry and drop out, leaving irregularly shaped holes in the leaves.
  • Angular leaf spot thrives in warm humid conditions.
  • It can move into new areas on seed and survive on plant debris.
  • Do not work in plants when leaves are wet.
  • Rotate vegetables so two or more years go by before planting any member of the squash family in the same location.

How to tell angular leaf spot from other cucurbit diseases

Green leaf with brown spots and holes from angular leaf spot.
The angled lesions of angular leaf spot
  • Leaves develop small, angular, brown or straw-colored spots with a yellow halo.
  • Leaf spots dry and drop out, leaving irregularly shaped holes in the leaves.
  • Spots are typically confined within leaf veins. 
  • Water-soaked tan, small circular spots on fruit.
  • Bacterial soft rot often develops after fruit spots and rots the entire fruit.
  • Sticky drops of whitish liquid form on the underside of the leaf when wet, dry to a crust when dry.

Biology

  • Angular leaf spot is a bacterial disease caused by Pseudomonas syringae pv. lachrymans
  • Although angular leaf spot can infect any of the cucurbit crops, it is less common on cucumber due to the availability of resistant varieties.
  • Angular leaf spot thrives in warm humid conditions.
  • The bacteria can infect all cucurbit crops and will infect all above ground parts of the plant including leaves, fruit and vines.
  • When bacteria infects the fruit, it moves deep into the fruit and infects the seed.
  • Contaminated seed can introduce the disease into a field.
  • When humidity is high, a drop of clear to white sticky bacterial ooze forms on infections. These bacteria move from plant to plant on the hands and tools of workers, by insects or by splashing water.
  • The pathogen can survive in plant debris for over two years.

Managing angular leaf spot in the home garden

Close-up of green leaf with brown holes and spots from angular leaf spot.
The underside of a leaf infected with angular leaf spot

Resistant varieties

Cultural controls

  • Buy clean seed from a reputable source. If saving seed, do not collect seed from infected plants.
  • Rotate vegetables so two or more years go by before planting any member of the squash family in the same location.
  • Use drip irrigation instead of overhead sprinklers if possible. If watering by hand, water at the base of the plant where the vine meets the soil. 
  • Do not work in plants when leaves are wet.
  • Remove and destroy infected fruit and vines at the end of the season in small gardens.

Managing angular leaf spot on farms

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Marissa Schuh, horticulture IPM Extension educator, and Michelle Grabowski

Reviewed by Natalie Hoidal, Extension educator

 

Reviewed in 2022

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