Leaf spot refers to the dead or necrotic regions on leaves that are caused by fungal or bacterial pathogens. When the spots expand into larger areas of dying tissue, this is known as blotch and if the large areas are quickly killed, the disease is described as blight (see What is blight). There are many diseases which are referred to as ‘leaf spot’. Here, we explore the most common leaf spot diseases and how to control them.
Septoria spp.
Septoria leaf spot, also known as Septoria blight or late blight (not to be confused with late blight of potatoes) is a widespread disease of fruits and vegetables. There are several species of Septoria that cause leaf spot and they are host specific, e.g. Septoria lycopersici only affects tomatoes while Septoria apiicola affects celery. As such, symptoms vary between plants, but generally begin as small spots that can grow and spread.
Small spots with red-brown margins and grey or tan coloured centres. The spots may coalesce and form large blotches. Fruiting bodies may be visible as small black dots on the spots.
Spots appear on the lower leaves and spread upwards towards the new growth. The spots may expand and if left untreated, cause leaves to yellow, wither and eventually fall. The fruits are not affected (black spots on tomato fruits are caused by anthracnose).
Spots appear on leaves, stems and fruits. The disease begins as small light brown spots which develop into larger patches, eventually covering most of the surface area. While the pulp is edible, it may ripen unevenly.
Small brown spots begin on the lower outer leaves and spread to the rest of the plant, including stems. The spots can combine and enlarge, causing whole leaves to collapse and wither.
Remove all diseased plants and practice crop rotation, avoiding planting in the same spot for 3-4 years. Avoid overhead watering and ensure there is enough spacing between plants. Treat with a suitable fungicide at first sight and repeat regularly if conditions are moist and humid.
All vegetables, including tomato, lettuce and celery: Yates Tomato & Vegetable Dust, Yates Leaf Curl Copper Fungicide Spray
Ornamental plants, including chrysanthemum and gerbera: Yates Leaf Curl Copper Fungicide Spray
Passionfruit and citrus: Yates Leaf Curl Copper Fungicide Spray
Alternaria passiflorae
Brown spot is a common disease of passionfruit. It affects all parts of the vine, including stems, leaves and fruit. The disease is prevalent during the warmer months and is spread by wind-blown rain.
On leaves, small brown spots appear first. These enlarge, develop a lighter-coloured central area, and become irregular or angular in shape. On fruit, spots first appear as dark green pinpricks, which enlarge into sunken circular lesions with brownish centres. Spots can develop into extensive superficial lesions causing premature drop and fruit decay.
Avoid a dense overcrowded canopy by thinning out bushy growth and remove dead or diseased plant parts. A healthy vine is better able to withstand a fungal attack, so feed regularly with Yates Thrive Natural Citrus & Fruit Organic Based Pelletised Plant Food and water regularly and deeply. At the first sign of disease, spray the entire plant with Yates Leaf Curl Copper Fungicide Spray every 7-14 days until the disease has been adequately controlled. Yates Leaf Curl Copper Fungicide Spray can also be applied as a preventative treatment - apply at monthly intervals in spring and summer, and two monthly intervals in winter.
Recommended Product: Yates Leaf Curl Copper Fungicide Spray
Venturia inaequalis
Also known as apple scab, this disease affects all parts of the tree, including leaves, buds, blossoms and fruits. It can significantly reduce yield and the overall health of the tree. It is closely related to the pear scab (Venturia pirina) and while symptoms are similar across both fruit trees, the pathogens are host specific, so pear scab does not infect apples nor does apple scab infect pears.
Small light green spots appear on either side of the leaves and eventually develop into dull green to grey lesions. Older spots are brown black and slightly raised. In severe cases, leaves may wither and drop. The fruit develops black spots and as they age, enlarge and become brown and corky in the centre. Fruit may be misshapen if infected in the early stages of development, but fruit affected near maturity will only have superficial markings.
The disease persists on fallen leaves, so rake and bin or destroy fallen leaves. Spray with a preventative fungicide like Yates Liquid Copper or Yates Lime Sulfur (as directed on the label) to help reduce the risk of re-infection. The disease favours moist humid conditions so keep an eye out on the leaves for early signs of infection. Treat at first sight with Yates Mancozeb Plus Garden Fungicide and Miticide.
Recommended Products: Yates Liquid Copper, Yates Mancozeb Plus Garden Fungicide and Miticide, Yates Lime Sulfur
Alternaria spp.
Alternaria is a widespread disease of various fruits and vegetables. There are many species of Alternaria which can infect plants and they can be host specific or attack a wide range of hosts. Many species are saprophytes, so they feed on dead organic matter and assist with the natural decomposition process. However, many species attack plants and cause issues with plant health and vigour.
Small dark brown flecks appear on leaves and develop into circular tan spots surrounded by a yellow halo. The spots can enlarge to blotches and in severe cases, cause blighting and subsequent death.
Alternaria produces masses of spores that are easily spread via wind or water splash. To help reduce the risk of infection, avoid overhead watering and remove any diseased parts or severely affected plants. Only plant disease free material and minimise plant stress by feeding and watering well.
Tomatoes and vegetables: Yates Leaf Curl Copper Fungicide Spray, Yates Tomato & Vegetable Dust (not on cucumbers)
Cercospora spp.
Cercospora leaf spot is a common disease of leafy vegetables, capsicums and cucurbits. It typically affects the foliage, but in wet, warm and humid conditions, it can also be visible on petioles and stems. The symptoms are often confused with Septoria leaf spot, but black fruiting bodies are typically visible with Septoria infections.
Leaf spots appear on the older leaves as small brown or grey flecks with a red-brown border. As they age, they become circular or oval with ash-grey centres. The centres become thin and brittle and may eventually fall out, leaving a hole. The spots are sometimes surrounded by yellow halos and in favourable conditions, will expand and join to form large blotches.
Practice crop rotation and avoid growing plants of the same species in the same spot for at least 3-4 years. Remove affected leaves and harvest leaves regularly – this prevents the pathogens from establishing. Spray with a suitable fungicide at first sight and repeat if conditions are wet, warm and humid. Avoid overcrowding seedlings at planting time and avoid overhead watering.
Recommended Products: Yates Leaf Curl Copper Fungicide Spray, Yates Tomato & Vegetable Dust (not on cucumbers)
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