Wednesday, November 9, 2011

Mango Anthracnose

  A mango tree may grow well but produce little or no fruit. 
This condition is likely brought on by a disease called mango anthracnose (Colletotrichum gloeosporiodes).  During the bloom period, when the weather is warm and wet, mango blossoms are attacked by this fungus.  The flowers are destroyed and little or no fruit is set.  This disease also affects other fruit trees throughout the world including banana, avocado, papaya and coffee. 
The fungus also occurs on the leaves, twigs and fruit.  On the leaves, it is seen as small angular brown/ black spots which can grow larger.  Sometimes the dead spots will dry and drop out leaving holes in the leaves.  Under wet conditions lesions on the stems may produce eye-catching pinkish-orange spore masses. Most of the infections on the green fruit remain latent until the fruit is ripe.  Then dark, sunken decay spots will develop and eventually will penetrate deep into the fruit. 

What to do.  1.  Plant resistant varieties, especially in wet areas. The following varieties are listed as moderately resistant - Carrie, Earlygold, Edward, Glenn, Julie, Keitt, Florigon, Tommy Atkins and Van Dyke.   The one tree that shows the best resistance to this disease is Florigon.
 2. Prune and discard plant material.  3. Spray with a copper fungicide when blooms first appear and continue until fruit is 1 ½ to 2 inches long.
It is difficult to grow mango in areas with high rainfall.  According to a UH publication, mangos are best adapted to hot, dry leeward areas receiving less than 60 inches of rainfall annually.
Some mango varieties, especially Haden and Pirie, tend to alternate bear.  That is they produce a large crop one year, followed by an ‘off year’ with low yields.