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.

Description

Black spot is one of the most common diseases attacking stems and leaves of potatoes. Spots can grow up to 20 mm wide, are angular in shape and appear leathery. Often circular sunken pits form which can develop into large sunken patches.

Leaf spots on tomatoes are oval with a yellow halo ranging from 6-12 mm wide. Stem lesions are elongated with lines, and fruit spots appear as sunken, ringed lesions which are dark brown to black and often cause fruit to rot. Severe infections can cause leaves to die and small seedlings can be destroyed when infected near ground level.

Black spot survives on infected crop residues and seeds from the previous year and spores are easily spread by wind, rain or insects infecting new seedlings.

Control

Reducing the disease load is important for the management of black spot so infected plants and seeds should be removed and destroyed after each crop. Healthy disease-free seed should be sourced for planting and infected foliage should be pruned to remove disease and improve air flow. Ideally crops should be rotated allowing breaks of 2-3 years and where possible, tolerant varieties planted.

Fungicides should be applied as a preventative measure prior to infection. Antracol® Fungicide Spray is registered for control of black spot in tomatoes and potatoes. Blueshield® is registered for black spot control in tomatoes and potatoes.

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.

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.

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.

References

Dopel, R (1960), ‘Black spot of tomatoes’, Journal of Agriculture Vol 1 No 5, https://researchlibrary.agric.wa.gov.au/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=1716&context=journal_agriculture4

Herbiguide (Viewed Oct 2019), ‘Target spot of potato, tomato and capsicum’, http://www.herbiguide.com.au/Descriptions/hg_Target_Spot_of_Potato_Tomato_and_Capsicum.htm

Pestnet (2017), ‘Tomato early blight’, Pacific Pests and Pathogens – Fact Sheets, http://www.pestnet.org/fact_sheets/tomato_early_blight_211.htm