Citrus Greasy Spot (Mycosphaerella citri), is a fungal disease that affects all citrus but especially grapefruit, lemon and tangelo. It is more prevalent during windy, humid and wet weather conditions, as wind disperses the its spores.
Plant Parts: Leaves and fruit.
Season: Spring to Autumn.
Symptoms: Leaf Symptoms: Initial yellow mottle pattern with reddish-brown blisters on the underside of the leaf. As the leaf ages, the lesions become darker brown with a greasy look. The yellow disappears and badly affected leaves will drop.
Fruit Symptoms: Symptoms appear as specks on rind between oil glands. Especially noticeable on grapefruit. Lesions start pink but become brown or black 3-6 months after infection.
Control: Applying a copper spray at petal fall (always read the directions of anything you apply on your fruit tree), this will help with control. The copper spray protects the developing fruit. If your fruit tree is heavily infected on foliage, follow up with another spray of copper in late summer.
Prevention: Remove dead leaves and fallen branches from around your tree. Clean up trees by pruning out deadwood, and don't leave any broken branches or dead leaves in or under your tree. Do not wet the canopy of the tree when watering.
Good balancing and removal of dead twigs from your fruit salad tree will help keep this fungal disease at bay as will an annual spray of copper in Spring and Autumn.
References: NSW Department of Primary Industries, QLD Department of Agriculture & Fisheries, Id Tools, University of florida, Citrus Foliar Fungal Diseases, Cabi, Photo Credits: M.M. Dewdney, L.W. Timmer, J.D. Burrow, and our FST team.
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