Powdery mildew

Powdery mildew affects grapes and apples and is one of the most widespread, persistent and damaging fungal diseases in both Australian vineyards and apple orchards.

Description

The first sign of the disease in both apple trees and grapevines is yellow blotches on the upper surface of leaves. The infected leaves also become curled or distorted. As the disease progresses, ash grey to white lesions covering all green tissue create the appearance of a powdery ‘mildew’. Grapes show typical mildew growth, while any apples that grow from infected buds are usually russetted.

Control

Frequent monitoring for signs of the disease is the first line of defence. Powdery mildew exists in every vineyard and most apple orchards, so knowing when and where to use control methods depends on accurate anticipation of growing disease pressure. The disease can spread very rapidly in shaded canopies when the temperature range is 16–30º C and relative humidity is moderate to high.

The two key timings for preventative use of fungicides in grapevines are during early rapid shoot growth and from pre-flowering to fruit set.

In apple orchards, Luna® Sensation is already regarded by some agronomists and growers as the most effective preventative option available. It has the added advantage of relieving the pressure of developing resistance on older chemistry

Related Pests

Black Spot Apples and Pears

Venturia inaequalis (Apple scab), Venturia pirina (Pear scab)

Black spot, also known as apple scab or pear scab, is a serious disease found in pear and apple growing regions across Australia. Whilst symptoms in apples and pears are similar, the disease is caused by different fungi and cross infection from one host to the other isn’t possible. Leaves and fruit at early development are highly susceptible and serious yield and quality reductions are likely if not managed properly, especially in wet seasons.

Symptoms in pears and apples are very similar and therefore have been described as such unless otherwise indicated.

Refer to links below for more information on black spot in other crops.

Alternaria leaf blotch and fruit spot

Alternari alternata, Alternaria arborescens, Alternaria longpipes, Alternaria mali, Alternaria tenuissima

Alternaria leaf blotch (ALB) and alternaria fruit spot can cause significant impact to apples. In Australia, ALB, is believed to be caused by several Alternaria species including A. mali, A. arborescens, A. alternata and A. tenuissima and A. longpipes. Research has shown the prevalent species in most regions across Australia largely causing leaf blotch is A. arborescens. The symptoms can vary from State to State with some regions experiencing very severe infections. ALB is more commonly found in New South Wales and Queensland therefore control measures can vary in different areas.

Downy mildew

Plasmopara viticola

Downy mildew is a sporadic disease that can have a devastating impact on grapevines when warm, wet conditions trigger the rapid spread of secondary infection.