Monday, November 24, 2014

Avocados with Black Strings



Why are some avocados stringy?

The strings in the fruit are vascular tissue, part of the conductive system of the plant bringing water and nutrients to the fruit.  They are always in the fruit but are unnoticeable in high quality fruit. From non-grafted trees, or seedlings where a genetic mix takes place, fruit can exhibit darkened, thicker strands as a natural characteristic, especially as it reaches maturity and beyond.  

These strands are usually the same color as the fruit pulp but can discolor or blacken for various other reasons. The most common reason is cold temperatures. This is true in avocado growing in areas like California where temperatures can reach freezing or below. Cold weather, however, would not apply to fruit growing in tropical regions such as the Hawaiian Islands. 

The blackened vascular tissue can also be caused by a disease. There are a number of fungi which enter an avocado at the stem end of the fruit.  Some of these pathogens will cause vascular discoloring as a precursor to decaying the flesh. 

These stem-end rotting fungi are present in the soil and on dead plant tissue and assist in the breakdown of organic matter. The spores of the fungi spread by wind and splashing water. This disorder is clearly made worse in a rainy environment. Infection typically occurs when the fruit is still on the tree, but it does not develop until after the fruit is picked due to anti-fungal compounds present in unripe fruit. Fruit will continue to decay as it ripens.


Control Measures For this Fungal Disorder 
  • Clean out dead limbs and twigs which helps to reduce the incidences of fruit rot.  
  •  Keep trees healthy with proper nutrients and water.
  • Maintain a thick layer of mulch under the tree’s canopy which will help to minimize the disease.   
  • Place avocados in the refrigerator after picking them, if not eaten soon. Caution: Temperatures below 41 degrees Fahrenheit can cause fruit injury in some varieties.
  •  Spray trees with a copper fungicide to limit infection if the problem is severe.