How to Manage Pests
UC Pest Management Guidelines
Oriental Fruit Moth
Scientific name: Grapholita molesta
(Reviewed 3/09, updated 11/12, pesticides updated 9/15, corrected 12/16)
In this Guideline:
DESCRIPTION OF THE PEST
Oriental fruit moth is an occasional pest of almonds. It overwinters as a mature larva in bark cracks and in leaf litter. The small brown moths emerge in late February. Larvae are white to pink with a brown head capsule. There are five to six generations per year.
First-and second-generation larvae mine young, tender shoots, causing them to wilt and die. Third- and fourth-generation larvae feed between the hull and shell; this damage is difficult to distinguish from that caused by peach twig borer. Damage is rarely significant. Occasionally, larvae have been found feeding on nut meats. They may feed in groups of several larvae within a nut. Larvae do not produce webbing but do produce a characteristic reddish brown frass in the hull.
Oriental fruit moth rarely causes significant kernel damage to almonds. Sprays are usually only required if significant damage by this pest occurred the previous year or in orchards that are near to other sources of oriental fruit moth (e.g. infested peach and nectarine orchards, which are harvested before almonds). Monitor oriental fruit moth densities in late April to early May by opening shoot strikes and looking for larvae, as described in the monitoring section for peach twig borer. Oriental fruit moth larvae will look distinctly different from peach twig borer larvae (reddish-brown with white intersegmental banding) and strikes occur after peach twig borer strikes. A harvest sample will help evaluate the effectiveness of your management program.
Monitoring and Treatment Decisions
Calculate degree-days for oriental fruit moth in your location.
Learn to use degree-days to time insecticide applications.
Adult oriental fruit moth populations can be monitored and treatments timed (if necessary) with pheromone traps. These should be placed in orchards by February 15 in the northern or eastern quadrant of the tree, 6 to 7 feet high. Use three traps per orchard or varietal block less than 30 acres. Use one trap per 10 acres for 30- to 80-acre orchards and one trap per 20 acres for orchards larger than 80 acres. Monitor traps once a week. Replace pheromone lures according to manufacturer's directions, and replace trap liners when dirty, or after counting and removing an accumulated total of 150 moths. Oriental fruit moth traps usually catch many more moths than do peach twig borer traps, and like peach twig borer traps, trap catch numbers are generally not a good indicator of potential damage.
To determine optimum time to spray, accumulate degree-days beginning with the first male moth trapped from the second flight, which usually peaks in late May. Use a lower threshold of 45°F and an upper threshold of 90°F. The optimum time to treat for oriental fruit moth is 500 to 600 degree-days after the first trapped male in any flight.
UC IPM Pest Management Guidelines:
Insects and Mites
F. G. Zalom, Entomology, UC Davis
Acknowledgment for contributions to Insects and Mites:C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter and Yuba counties
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
R. A. Van Steenwyk, Insect Biology, UC Berkeley
R. E. Rice, Kearney Agricultural Center, Parlier
L. C. Hendricks, UC Cooperative Extension, Merced County
R. L. Coviello, UC Cooperative Extension, Fresno County
M. W. Freeman, UC Cooperative Extension, Fresno County