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Angular Leaf Spot

  • Photograph of Angular leaf spot on a strawberry leaf
    Symptoms on the lower leaf surface. Image courtesy of Umberto Mazzucchi, Mazzucchi & Dalli 1973.
  • Photograph of a close up of Angular leaf spot on a strawberry leaf
    Close up of symptoms on the lower leaf surface. Image courtesy of Umberto Mazzucchi, Mazzucchi & Dalli 1973.

General information

Xanthomonas fragaria is an exotic bacterial pathogen of strawberry. The pest poses a significant production threat to the strawberry market. Angular leaf spot (ALS) disease primarily destroys the leaves of strawberry plants and on occasions, also affects the plant's flowers. It does not affect the fruit grown on infected plants, but has the potential to significantly reduce the performance and yield capacity of an infected strawberry crop. The bacterium does not affect human health.

Overview

Cause Bacterium Xanthomonas fragaria.
Other names Leaf blight of strawberry, vascular collapse of strawberry.
Description
  • Symptoms develop on strawberry leaves and sepals.
  • Initial symptoms are small angular, water-soaked, translucent spots on lower surface of leaves.
  • As disease progresses, spots enlarge and appear on upper surface of leaves.
  • In severe case, affected leaves dry and turn reddish-brown.
Distribution
  • Widespread in many strawberry productions areas in the United States and Canada.
  • Has restricted distributions in European countries. Considered a quarantine disease by the European Union.
  • Australia is currently free of ALS.
  • Has been eradicated in Australia each time it’s been detected.
Lifecycle
  • Infected transplants or systemically infected overwintered plant debris in fields are primary inoculums of ALS.
  • Bacterium is unable to survive freely in the soil but can survive for long periods in debris.
  • In favourable conditions, the bacterium infects young leaves of a new crop at growing season.
  • In fields, bacterial exuded from infected leaves serves as a secondary source of inoculum.
  • Disease easily spreads by splashing water from rain or overhead irrigation, as well as harvesting operations.
Crops affected
  • Cultivated strawberries are only host of concern.
  • Disease susceptibility varies depending on the cultivars.
Hosts Strawberry plants
Symptoms
  • Early symptoms form on underside of leaves as small, angular, water-soaked spots.
  • As infection advances, reddish brown spots (1-4mm across) develop on upper leave surface and cause death of tissue.
  • Daylight can usually be seen through angular spots on leaf.
  • Spots lose together may join to form large areas of dead leaf tissue, giving plant blotchy appearance.
  • If left unchecked, tissue damage may become severe and kill plant.
Impacts
  • Presents a significant risk to Queensland strawberry industry.
  • Doesn’t directly infect fruit, but infection generally causes stress to the plant and reduces fruit quality that downgrades market values.
Spread
  • Readily distributes through infected nursery stock or other infected plant material.
  • Water splash and wind help local spread of bacteria.
Risk period
  • Favoured by prolonged leaf wetness caused by frequent rain, overhead irrigation, or heavy dews.

Monitoring and action

Report any possible symptoms immediately to Biosecurity Queensland on 13 25 53.
Control

For chemical control, copper-based sprays are used to prevent or reduce infection levels, although this does not guarantee a disease-free crop.

Cultural practices are also used, including:

  • using disease-free planting material
  • wide row spacing
  • planting in free-draining soils
  • not moving equipment through plants when they are wet
  • not using  of overhead sprinklers during plant establishment.

Quarantine restrictions

If the disease is suspected, please call Biosecurity Queensland on 13 25 23. In Queensland, angular leaf spot of strawberry (Xanthomonas fragaria) is prohibited matter under the  Biosecurity Act 2014.