Q: The oldest leaves on my coconut tree have turned yellow. How can you tell the difference between lethal yellowing and if the tree just needs fertilizer?
A.H., North Miami Beach
A: Look at the flowers and fruit of your palm. Are the nuts falling before they are mature? Are the mature nuts ''shelling'' or are the flowers turning brown? These are typical signs of lethal yellowing. Fallen nuts from an infected palm have a dark-brown to black, water-soaked zone at the stem end.If the palm is suffering from severe potassium deficiency, the flowers and fruit will be normal. As the oldest fronds yellow, the leaf tips and margins will turn brown. Initial signs are translucent yellow or orange flecks on the leaflets, with or without brown spots.
Correcting nutritional deficiencies in palms is slightly complicated. To do it correctly, call your local Extension office (305-248-3311 in Miami-Dade, 305-292-4501 in Monroe, 954-370-3725 in Broward) for advice or read this fact sheet about potassium deficiency: http://edis.ifas.ufl.edu/EP269
Adrian Hunsberger is an entomologist/horticulturist with the UF/IFAS Miami-Dade Extension office. Write to Plant Clinic, 18710 SW 288th St., Homestead, FL 33030; e-mail aghu@ifas
.ufl.edu
