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Angular leaf spot

Quick facts

  • Angular leaf spot can infect any of the 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.
  • When bacteria infects the fruit, it moves deep into the fruit and infects the seed.
  • 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.

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.

Green leaf with brown spots and holes from angular leaf spot

Identifying angular leaf spot symptoms

  • 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.
  • 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.

What causes angular leaf spot

  • 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.
Close-up of green leaf with brown holes and spots from angular leaf spot

Preventing and managing the disease

  • Many resistant varieties are available for cucumbers and are the best form of control for this crop.
  • 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.
  • 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.
  • In large fields, till in infected plant debris at the end of the season to speed up decomposition.
  • Copper can slow the spread of disease if used early. Sprays are not effective once disease is severe. Do not continue sprays if dry weather persists beyond two weeks.

Michelle Grabowski

Reviewed in 2018

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