Strawberry angular leaf spot

Alert

Have you seen Strawberry angular leaf spot?

Be on the lookout and report it.

Under Queensland legislation if you suspect the presence of Strawberry angular leaf spot, you must report it to Biosecurity Queensland on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

Early detection and reporting are key elements in controlling Strawberry angular leaf spot.

Strawberry angular leaf spot is a disease of strawberries. It is not currently present in Australia.

The disease poses a significant threat to strawberry production. Angular leaf spot disease primarily destroys the leaves of strawberry plants and can occasionally affect the plant's flowers. Fruit is not affected but performance and yield capacity of an infected strawberry crop can be significantly reduced.

Cause

Strawberry leaf spot is caused by the bacterium Xanthomonas fragariae.

The bacterium does not affect human health.

Other names

  • Leaf blight of strawberry
  • Vascular collapse of strawberry

Description

Symptoms

  • Symptoms can vary depending on the plant variety, weather conditions, and time of year.
  • The first spots usually develop on the lower leaf surface. They are small angular, water-soaked and translucent. Daylight can usually be seen through them.
  • As the disease progresses, the spots turn reddish brown (1–4mm across) and are visible on both leaf surfaces.
  • Spots close together can join to form large areas of dead leaf tissue, giving plant blotchy appearance.
  • Dead leaf tissue in the spots can tear and fall out.
  • The fruit cap or calyx can develop a brown or blackened appearance.
  • If left unchecked, tissue damage may become severe causing defoliation and killing the plant.

Plant stage and plant parts affected

The disease affects above ground plant parts excluding fruit.

May be confused with

There are several other pathogens that cause leaf spots

Strawberry angular leaf spot is distinctive as the leafspots are angular in shape, and when the spots are in the translucent stage and held up to the light, the light can shine through them.

Distribution

Strawberry angular leaf spot is found in many overseas countries that produce strawberries, though the distribution of the disease in those countries may be limited.

Australia has successfully eradicated this disease each time it has been detected.

Australia is currently free of strawberry angular leaf spot.

Hosts

  • Strawberries.
  • Disease susceptibility varies depending on the cultivar.

Life cycle

  • Initial infection in a new area is usually caused by the introduction of infected plant material.
  • The bacterium can survive for long periods in infected plant debris in the soil which can become another source of the bacterium.
  • In favourable conditions, the bacterium infects young leaves of a new crop.
  • Under moist, humid conditions, the leaf spots exude a milky, bacterial ooze.
  • The bacteria are easily spread by splashing water from rain or overhead irrigation, as well as by harvesting operations.
  • The disease is favoured by prolonged leaf wetness caused by frequent rain, overhead irrigation, or heavy dews.

Impacts

Strawberries are an important crop in Queensland. Approximately 150 growers are involved in the industry, and farms range in size from 5,000 to 5 million plants. The industry is worth about $130 million to the Queensland economy.

Strawberry angular leaf spot presents a significant risk to Queensland strawberry industry. The disease is difficult to control, and while the disease doesn't directly infect fruit, it causes stress to the plant and reduces fruit quality that downgrades market value. Infected nursery plants may be subject to quarantine.

If the disease were to be found in Queensland, home growers of strawberries could also be affected.

How it is spread

The disease readily spreads long distances with the movement of infected nursery plants (e.g. strawberry runners or potted plants) or other infected plant material such as debris.

Localised spread of the bacterium within a field is caused by water splash (rain of irrigation) and wind currents.

Monitoring and action

Regularly check your strawberries for angular leaf spots.

Look for translucent leaf spots that the light can shine through if you hold the leaf up to the light.

Advance symptoms include reddish brown leaf spots, blotchy leaf spots that tear and fall out giving leaves a tattered appearance and brown or black coloured calyxes on fruit.

Report suspected strawberry angular leaf spot to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

Legal requirements

Strawberry angular leaf spot is prohibited matter under the Biosecurity Act 2014.

Report suspected strawberry angular leaf spot to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

If you think you have found the disease, you must take all reasonable and practical steps under your control to minimise any associated risks. This is called a general biosecurity obligation (GBO).