Entomosporiosis: prevent and control

Which species are susceptible to Entomosporiosis?

In the ornamental garden

Foliage of Hawthorns, Juneberries, Cotoneasters, Photinias, Japanese loquats becomes speckled and causes damage of an aesthetic order.

In the orchard

Quince in particular is very susceptible to Entomosporium leaf spot but it can also affect apple and pear trees. Foliage, and also fruits in case of a severe attack are affected.

How to recognise entomosporiosis?

Numerous small round spots 1–3 mm in diameter (Amelanchier, Cognassier) or angular (Aubépine, Cotoneaster), reddish then covered with characteristic brownish crusts that can merge mark the lamina of youngest leaves. In case of severe attack, leaves turn yellow and fall.

On older leaves, spots darken with at the centre an area that becomes grey necrotic surrounded by a brown to dark red margin. Small black pits, the spores, are often observed at the centre of spots. The infection can extend to petioles and young shoots in cool, damp conditions, which leads to weakening of the tree.

Fruits may also be marked with necrotic spots, crack and mummify in severe cases. They become unfit for consumption.

Factors favouring Entomosporiosis

Fungus Entomosporium maculatum develops mainly in wet weather in spring and summer, when temperatures are below 20 °C. A dry spell, by contrast, slows disease.

During winter, the fungus survives on dead leaves, twigs and trunks of infected trees. It produces spores during wet periods, carried by wind and rain, which will infect trees in spring or even later, particularly at fruit formation. Spots appear 10 to 14 days after infection.

Control and treatment of Entomosporiosis

Curative measures against this disease :

• Remember, when pruning, disinfect your tools with 90% alcohol or vinegar to avoid transferring fungus from one branch to another.
• Avoid planting too densely and encourage aeration around and within the crown.
• Collect and burn infested leaves and fruit that have fallen to the ground.

Treatments :

• Prepare a solution of 20 g of Bordeaux mixture per litre of water as soon as first symptoms appear and spray :

1. in autumn, at leaf fall,
2. at the start of spring: one spray at bud swelling (bud burst period) and a second spray one month later.
3. During a particularly wet spring or as soon as first signs of spotting appear, repeat the treatment several times until fruit formation.

On Photinias, spray this solution :

1. in May,
2. then one month later, in June

For more about copper-based treatments, consult our advice sheet