Brown Rot of Citrus Phytophthora citricola, citrophthora & hibernalis
Citrus Collar Rot
A fungal disease that affects citrus leaves and fruit. On Oranges and Mandarins a grey-brown, firm rot forms on the fruit and they fall. On Grapefruit and Lemons the rot is yellow-brown. It has a distinctive odour. The leaves may have grey-brown to dark brown tip and edges and may fall when green. In severe cases whole shoots may be affected.
The Collar Rot form attacks the base of the trunk where gum may ooze from the bark, a wet looking patch may appear on the trunk, which may later dry out and split. Eventually it may girdle and kill the tree. Leaves may turn yellow as nutrients are restricted.
Citrus. In order of susceptibility are Eureka and Lisbon Lemons, Washington Navel and Valencia Oranges Rough Lemon rootstock, Grapefruit then Mandarins. Trifoliata and Troyer and Carrizo Citrange are resistant
Favoured by wet weather.
Lives in the soil.
Spread by raindrop splash.
Most common in autumn.
Origin and History:
The Collar Rot form is unlikely to be significant unless the trunk is wet for a long time.
Management and Control:
Prune trees so the lowest branches are at least 300 mm above ground.
Control tall weeds under trees to reduce humidity. Use a mulch.
Avoid over watering and keep the bas of the trunk dry.
Plant trees with the graft union 50-150 mm above the ground level.
Use Trifoliata and Citrange rootstocks if Collar rot is a problem.
Areas affected with collar rot should be cut away from the trunk and bituminous paint applied to the wounds.
Related and Similar Species:
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