Wednesday, September 21, 2011

Aphids

The new leaves of a citrus tree are all curled.  What is causing this?
During the period of a growth flush, when the new shoots are expanding and the leaves are still in the bud stage, small insects called aphids will feed on these shoots in large numbers.  Aphids have piercing mouthparts, much like a hypodermic needle, extracting vital nutrients from the plant and injecting hormones into the plant.  So when the new leaves finally come out, instead of being large and flat, they are small and curled.  Treating the trees at this point, when the leaves are already showing signs of curling, would be too late. 
Trees need to be inspected when the new shoots are expanding.  The time to treat is when the black, or sometimes, green aphids are seen.  A good treatment for aphids is to spray with a proper horticultural oil or horticultural soap.  The following is a University of Hawai`i recipe which combines both of these active ingredients: first make a concentrate of one tablespoon mild dishwashing liquid and one cup of vegetable oil.   When ready to use, shake well and mix 1 – 2 ½  teaspoons of the this mixture into one cup of water.  Spray plants thoroughly. Repeat sprays may be needed at 5-7 day intervals.  Do not spray in the heat of the day.