Photo 2. Symptoms of tomato powdery mildew, Leveillula taurica, on the underside of a chilli leaf. Note the patches are bordered by the main veins.
Tomato powdery mildew
Leveillula taurica. Other names are Erysiphe taurica and Oidium sicula. It exists as different strains. There are other powdery mildews affecting tomato. They are: Oidium lucopersici and Oidium neolycopersici.
Worldwide. In the tropics, sub-tropics and temperate countries. Asia, Africa, North, South, Central America, Caribbean, Europe, Oceania. It is recorded from Fiji (Euphorbia species), New Caledonia (capsicum, globe artichoke,tomato, Tropaelum), Papua New Guinea (Drymaria, Euphorbia, Oxalis), Solomon Islands (Euphorbia species), and Tonga (capsicum, Euphorbia species).
Tomato, capsicum, chilli, eggplant and others in the potato (Solanaceae) family, as well as members in the cotton (Malvaceae), onion (Amaryllidaceae), cucumber (Cucurbitaceae), legumes (Fabaceae), carrot (Apiaceae), and Euphorbia species (Euphorbiaeae) families, and more. It is particularly known as a disease of onion.
A major disease of tomato and many other crops, ornamentals and weeds. Generally, the lower leaves are infected first and then the disease moves up the plant. Whitish powdery patches of the fungus occur on the underside of leaves, causing mild distortions. Sometimes the fungus is restricted by the main leaf veins. On the top side of the leaf there are yellowish irregular-shaped spots, turning brown with age, and shriveling. Unlike other powdery mildews, the fungus does not grow much over the leaf surface; it is inside the leaf, and the spores form on long stalks growing out of natural openings.
On the top surface of the leaves, the yellowish spots and patches look like those of tomato leaf mould (see Fact Sheet no. 076), but there are no velvety spore masses on the underside typical of leaf mould.
Spread is by spores on the wind. Germination and infection occurs at temperatures under 30°C, and at medium to high humidity. Powdery mildews do not need water on the leaf surface for germination, but humidity must be sufficient.
A common and potentially serious disease during warm, dry weather. It can lead to loss of leaves, and early ripening and sunscald of the fruit (see Fact Sheet no. 085). In commercially grown tomatoes in the USA, yield losses may exceed 50%, depending on the age of the crops when the disease occurs, environmental conditions and effectiveness of fungicide control.
Look for the yellow spots and patches on the leaves somewhat bounded by the main leaf veins. Look on the underside of the leaves for white patches of spores protruding through the surface (there is little cottony growth over the leaf blade with this powdery mildew).
Check company descriptions of varieties. Resistance has been found in cucurbits, chilli and onions, but note that there are strains of the fungus and crop varieties may not be resistant to all of them. And note, there are many species of powdery mildew and crops resistant to one may not be resistant to others.
Cultural control and the use of resistant varieties should be sufficient to manage this disease. If the disease is known to be a problem, and based on previous experience fungicides are likely to be needed, inspect the crop regularly to detect when infections first occur. Start spraying immediately symptoms are seen, and spray routinely every 7-10 days, depending on the severity of the disease. Do the following:
AUTHORS Grahame Jackson & Eric McKenzie
Information from CABI (2016) Leveillula taurica (powdery mildew of cotton) Crop Protection Compendium (www.cabi.org/cpc). Photos 1&2 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Leveillula taurica. PaDIL - (http://www.padil.gov.au).
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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