Lychee webworm lifecycle and control
on lychee and longan in Florida

Jonathan H. Crane, Tropical Fruit Crop Specialist, University of Florida-TREC, Homestead

Dr. Jorge Peña, Entomologist and his laboratory staff at the UF-Tropical Research and Education Center has studied the life cycle of the lychee webworm, the  efficacy of control of the moth pest by an egg parasitoid, Trichogramma platneri, and the efficacy of a number of biopesticides and pesticides.  To date they have determined the adult moth is most active from 6:00 PM to 9:00 PM and that the adult moth oviposits (lays eggs) on apical buds (both vegetative and reproductive/flower panicles).  The eggs hatch and the larvae may bore into the succulent new terminal growth and/or feed on newly emerging flower parts.  Symptoms of damage include sudden wilting and death of newly emerging terminal shoots and webbing of newly emerged panicles or leaves.  Very small, recently set fruit (green, pea size) may also be bored into (they’ll show an entry hole).

The lychee moth has about a 35-day life cycle depending upon temperatures.  The moth population begins to build up during November, peaks during January and February, and remains noticeable through March.  No alternative host plants have been found and so it is suspected the moth maintains a very low population in lychee and longan groves from March/April to October.  This population of this moth pest appears to follow the flowering and flushing cycle of lychee and longan.

Current control recommendations for the lychee webworm include monitoring your grove closely from November through February and treating trees with INTREPID if the infestation warrants it.  Growers should scout their groves frequently (perhaps daily) by inspecting emerging new terminal shoots for eggs (round and off-white) which are laid adjacent to new buds, for signs of wilted or dead terminal shoots, webbing, and very young fruit bore holes.  Preliminarily it is recommended that if 3 of 10 randomly inspected terminal shoots show signs of the lychee moth (eggs) or damage that application of INTREPID begin.

INTREPID may be purchased at local chemical dealers.  Ask for the chemical dealer for the lychee and longan label information upon purchasing the material.  You must have this paperwork in your possession when applying INTREPID.  The lychee webworm larvae must consume INTREPID in order for the material to work.  Briefly, the maximum application rate of the product is 20 ounces per acre.  However, Dr. Peña has found a 10 ounce rate works as well as the higher rate.  The INTREPID should be applied every 3 to 4 days.  This short application interval is important in order to protect new growth since the last application with INTREPID and to control newly emerging larvae.  Producers should monitor their groves for signs of damage between applications, as it may not be necessary to continue additional applications if control is achieved with 2 or more applications and to monitor the extent of control.  A maximum of 120 ounces of INTREPID is allowed per acre per year.

Producers requiring more information and/or assistance with interpreting the Specific Exemption label please contact Dr. Carlos F. Balerdi, Multi-County Tropical Fruit Crops Extension Agent at 305-248-3311 x.233, Dr. Jonathan H. Crane, Tropical Fruit Crop Specialist, at 305-246-7001 x.290.