Frosty glasses of freshly squeezed juice from luminous orange fruit are rewards of growing your own sweet or navel orange tree (Citrus sinensis). Others are the haunting scent of white or pink blossoms and the year-round shade of a glossy green-leaved canopy. The bad news is that orange tree fruit, flowers and foliage face attacks of voracious thrips insects wherever they grow in U.S. Department of Agriculture plant hardiness zones 9 through 11.
At least one of five thrips species -- citrus, North American bean, greenhouse, chilli and Florida flower thrips -- targets orange trees in Georgia, Florida, the Gulf Coast states, Nevada, Arizona, California and Hawaii. Greenhouse thrips also plague orange trees in nurseries and greenhouses across the United States. While bean thrips concentrate on sweet and navel oranges, the others threaten all citrus species and their hybrids.
These four-winged pests range in size from 1/50-inch citrus to 1/12-inch chilli thrips. Yellow legs and brown body hairs distinguishing the yellow Florida flower thrips from citrus and chilli thrips. Brownish-black greenhouse thrips have white legs, while grayish-black North American bean thrips have alternating light and dark wing bands. Determining which type of thrips has found your tree, however, takes a back seat to preventing their damage.
With the exception of bean thrips, these insects feed by puncturing an orange tree’s buds, young leaves or fruit and draining the cell contents. Brownish-yellow buds or petals, prematurely dropping flowers and distorted leaves with curling, bronzing or silvering signal thrips’ presence. Scablike gray scars blemish infested fruit rinds. Bean thrips' offense is to burrow into the fruit's navels and overwinter, making the oranges unmarketable.
Monitoring for Thrips
Preventing damage begins with monitoring your orange trees regularly for thrips. Monitoring can be as simple as spreading a white drop cloth under the plants and shaking their branches to dislodge the pests. If necessary, use a rake to reach the branches. Another option is to hang square yellow sticky traps available at garden centers from the branches to catch the incoming insects.
Because thrips damage is primarily cosmetic, control measures are seldom necessary. The best approach is to prune and dispose of infested new growth, cutting each branch back to a leaf node or branch crotch so you don't stimulate even heavier shoot production. Thinning the canopy's interior may entice predatory mites to its exterior, where they attack citrus thrips feeding and laying eggs on the fruit.
Chemical pesticides have minimal effect on flying adult thrips and nymphs feeding within plant tissue. Only slow-moving greenhouse thrips colonizing leaf surfaces succumb to them. An insecticidal soap of 5 tablespoons of liquid dish detergent per gallon of water sprayed to saturate the leaves kills the greenhouse thrips it reaches. Repeating spraying every five to 10 days destroys newly hatched nymphs and recently pupated adults. The downside is that it also kills thrips-destroying mites.