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

CauseThe disease is caused by a bacterium Xanthomonas fragaria.
Symptoms

Early symptoms of ALS form on the underside of leaves as small, angular, water-soaked spots. As the infection advances, reddish brown spots (1 – 4 mm across) develop on the upper leave surface and cause the death of tissue. Daylight can usually be seen through the angular spots on the leaf.

Spots are close together may join to form large areas of dead leaf tissue, giving the plant a blotchy appearance. If left unchecked, tissue damage may become severe and kill the plant.

What do you do if you find symptomsReport any possible infections immediately to Biosecurity Queensland on 13 25 53.
Susceptible plans (hosts)ALS is a host specific disease. The only known susceptible host of angular leaf spot is strawberry plants.
Infection and spreadThe disease is favoured by prolonged leaf wetness caused by frequent rain, overhead irrigation, or heavy dews. ALS is readily distributed through infected nursery stock or other infected plant material. Local spread of the bacteria is by water splash and wind dispersal.
Where angular leaf spot occursThe infection attacks the leaves of strawberry plants. In some cases, the bacterium has also been known to infect strawberry flowers, but does not directly affect fruit. 
SignificanceALS presents a significant risk to the Queensland strawberry industry. Although this pathogen does not directly infect the fruit, infection generally causes stress to the plant and the quality of fruit is significantly reduced.
Human healthALS does not affect human health.
Management and quarantine Each time it has been detected in Australia, ALS has been eradicated in order to protect the strawberry industry from the disease.  Internationally, copper sprays are used to prevent or reduce infection levels, although this does not guarantee a disease free crop. Cultural practices are also used, including use of disease-free planting material, wide row spacings and planting in free-draining soils.
Under Queensland legislation the suspected presence of the pest must be reported to a Biosecurity Queensland inspector within 24 hours of the property owner becoming aware of it.

Last updated 14 September 2017