Monday, June 29, 2015

Green Algae Causes Leaf Spots on Avocados

Avocado trees, along with mangoes, can be attacked by a green algae called Cephaleuros virescens.  Most leaf spots are caused by fungi or bacteria. Occasionally, an alga will cause such spots with frequent rains and warm temperatures. The algae are dispersed by wind and splashing water. In addition to avocados and mangoes, about three hundred different plant species  are susceptible to this problem including guava, breadfruit, cacao, kava, tea (Camellia sinensis) and some citrus. 

Typically, green algae causes minor leaf spotting. Yet poor plant nutrition, poor soil drainage and stagnant air can predispose a tree to infection. On avocado and mango, the leaf spots appear burnt-orange to rust colored. On guava, the leaf spots are more brown or black, often with a yellow halo around each spot. The fruit can also be spotted, causing a scabby or scarring appearance, often affecting the marketability of the fruit. The algae do not cause a soft rot of the fruit. When attacking coffee, the algae is called ‘red rust’.

Again, with avocados and mangoes, there is generally no damage to the plant’s vigor or yield. Treatment is rarely needed.  Leaves on low hanging branches are mostly attacked. If desired, the low hanging branches that are affected may be pruned. Here are two recommendatons: keep the tree well fertilized and weeds under control. Copper fungicidal sprays, although usually not necessary, will control the disease.