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.

Description

Apples are more susceptible to leaf infections than pears and symptoms appear as light green spots on upper or lower leaves, which turn brown, then black with raised blistered spots. Severe infections can produce distorted leaves and defoliation. Infected flower stalks develop black patches which extend, causing the flowers to shrivel and die.

Early fruit infection can cause distortion. Late infections on mature fruit appear as small spots which become darker as they grow and older lesions turn brown, dry looking and corky with cracks. While fruit growth is stunted and appears distorted, the lesions are superficial and the flesh is not affected. Fruit infected before harvest may not be noticed until later in storage, causing storage scab. Twig infections are common in pears, which appear as brown lesions before eventually forming into corky canker-like areas.

The fungus mainly survives as ascospores on infected leaves, twigs and bud scales from the previous season. Primary infection occurs when spores are released following rain and spread via wind onto trees. For infection to be successful, leaf moisture and ideal temperatures (12.8 – 23.9 °C) are required. Lesions from primary infections cause secondary infections by producing spores which further spread and infect other trees.

Control

Successful management of black spot in apples and pears relies on the use of several control practices. A post-harvest application with urea helps breakdown leaf material, in addition, the removal of infected leaves and fruit will reduce the risk of infection. Pruning to maintain an open canopy improves air flow, allows faster drying times and enables better coverage with fungicides.

Control with fungicides aims to prevent primary infections early in the season, which subsequently reduces the likelihood of secondary infections. Post-harvest fungicide applications aim to prevent fungus surviving on leaves over winter.

Luna Sensation and Blue Shield are registered for control of black spot (scab) in apples and control of black spot (scab) in pears. Luna® Sensation and Blue Shield® should be applied early before disease symptoms appear.

Related Pests

Black spot

Elsinoe ampelina (grapes - anthracnose), Alternari solani (tomatoes, capsicums and potatoes - target spot or early blight), Venturia inaequalis (apple and pears - apple and pear scab), Guignardia citricarpa (citrus), Xanthomonas campestris (mangoes - bacterial black spot), Phoma medicaginis var. pinodella, Ascochyta pisi (field peas - black spot complex)

A number of horticultural crops are challenged by black spot, which is also referred to by a number of names. It affects grapes where it is also known as anthracnose. Black spot affects apples and pears and is also known as apple scab and pear scab. In mangoes, black spot is caused by a bacteria rather than a fungus and is referred to as bacterial black spot. In broadacre, field peas are also affected by black spot.

Black spot Grapes

Elsinoe ampelina

Black spot, also known as anthracnose in grapes, is a serious disease, particularly in areas which experience cool wet springs which favour disease outbreak. Currently it is successfully managed with fungicides, however prior to their introduction, blackspot was a major problem. Table grape varieties including sultana and red globe are more prone to black spot than wine grapes. Once established black spot is unrelenting and regular treatments are required to manage it.

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

Blackspot of field peas

Mycosphaerella pinodes, Phoma mediccaginis var. pinodella, Phoma koolunga, Ascochyta pisi

Commonly referred to as ascochyta blight, blackspot is one of the most serious diseases of field peas and is widespread in Victoria and South Australia. In field peas, blackspot is produced by four different pathogens, producing symptoms that are indistinguishable from each other. Yield losses of up to 60 per cent have been reported, particularly in wet seasons.

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

Black Spot Tomatoes and Potatoes

Alternaria solani

Black spot, also commonly known as early blight or target spot, is a serious fungal disease affecting vegetables belonging to the Solanaceae family. Disease hosts include tomatoes, potatoes, capsicums and eggplants. Outbreaks are favoured by warm, wet growing conditions and yield losses can be significant.

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

Mango bacterial black spot

Xanthomonas campestris pv. mangiferaeindicae

Bacterial black spot (BBS) was first found in Australia in the early 1980’s and it now appears in most northern mango growing areas of Australia. It has the potential to be a serious disease of mangos, in some cases up to 90 per cent of fruit is discarded due to spots on fruit deeming them unacceptable for market.

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

References

Agriculture Victoria (2003), ‘ Apple Scab’, Agriculture Victoria, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/fruit-and-nuts/pome-fruit-diseases/apple-scab

Department of Primary Industries (DPI) NSW (Viewed Oct 2019), ‘Apple and Pear Scab’, https://www.dpi.nsw.gov.au/agriculture/horticulture/pomes/pests-etc/apple-and-pear-scab

Hetherington, S and Munroe, A (2009), ‘Integrated pest management for Australian apples and pears – Apple Scab (Black Spot), Pear Scab’, The State of New South Wales, Industry and Investment NSW, Apple and Pear Limited pg 40 – 50, https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0009/321201/ipm-for-australian-apples-and-pears-complete.pdf

McCarthy, A (2018), ‘Managing apple scab in Western Australia’, Department of Primary and Regional Industries (DPRID), https://www.agric.wa.gov.au/pome-fruit/managing-apple-scab-western-australia?page=0%2C2#smartpaging_toc_p2_s0_h2

Washington, W and Villalta, O (2006), ‘Pear Scab’, Agriculture Victoria, Note Number AG0159, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/fruit-and-nuts/pome-fruit-diseases/pear-scab