Fungal Diseases of the Avocado Tree

The avocado tree or Persea americana, grown primarily in tropical to subtropical climates, produces a tasty fruit, known as the avocado or alligator pear. According to the Texas A&M University Extension, the most popular avocado plant grown in the United States is the Mexican or Mexican-Guatemalan hybrid variety. The trees exhibit hearty growth during normal growing conditions, but can take up to 15 years to produce fruit. Although the tree exhibits hearty growth in prime growing conditions, it is susceptible to a variety of diseases that can reduce crop yield and damage the tree.

Anthracnose

Anthracnose is one of the most common and devastating diseases that affects the avocado tree and fruit. Caused by the fungal pathogen Colletotrichum gloeosporioides, anthracnose infects the flowers, fruit, leaves or twigs, according to the University of California at Davis. Symptoms of infection include, yellowing and browning of the leaves, premature leaf drop, necrosis between the leaf veins and on the margins, shoot dieback and legions on the fruit. According to the University of California at Davis, black legions less than 0.2 inches in diameter develop on the fruit while still growing on the tree, and then further develop during the ripening period. The legions can spoil the fruit by rotting the soft flesh interior. Control for anthracnose includes pruning out dead limbs and twigs, pruning infected limbs and twigs and the use of copper-based sprays to prevent the fungal infection.

Cercospora Spot

Caused by the fungal pathogen Cercospora purpurea, Cercospora spot infects the leaves and fruits on the avocado tree. Symptoms of the disease consists of leaf spot with surrounding yellow haloes, grayish spore infestation, brown spots on the skin of the fruit and fissures on the infected spots, according to the University of Florida. The fungus reproduces and infects more often during periods of heavy rain, especially during the months of May through September. Control for Cercospora spot consists of systemic fungicide application during the growing season.

Powdery Mildew

Powdery mildew is a disease that is caused by a variety of different fungal pathogens, and infects almost every type of plant. According to the Cornell University, symptoms of a powdery mildew infection consist of dusty white powder coating on the leaf, leaflets or stem. The powdery mildew pathogens prefer humid climates, which typically occurs later on during the growing season. Plant damage is relatively low if treated early, but can result in yellowing and death of infected tissue, premature leaf drop and stunted growth, according to the Cornell University. Control for a powdery mildew infection in avocado trees consists of using fungicides, physically removing the fungal growth with a hose or by hand and use of natural fungicides.

Sources:

http://aggie-horticulture.tamu.edu/extension/homefruit/avocado/avocado2.html

http://www.ipm.ucdavis.edu/PMG/r8100711.html

http://plantclinic.cornell.edu/FactSheets/powdery/powdery.htm

http://edis.ifas.ufl.edu/vh047