Information from Dr. Vince Jones, Dr. Ute Chambers, WSU Entomology; and Dr. Jay Brunner, WSU Emeritus.  Summarized by Tianna DuPont, WSU Extension. March 2017.

Horticultural oil is important for control of codling moth eggs. All eggs that the materials contact (regardless of egg age) will be affected. Larvae will also be impacted if they try to eat the oil, killing about 30%. Because contact is necessary, coverage is critical. The residue will be gone in a day or two. In addition to codling moth, horticultural oil affects mites, aphids, and San Jose scale and is relatively easy on most natural enemies.

The first oil spray should be applied before egg hatch which is at 375 degree days (DD).

Application of oils at 375 DD kill eggs that are about to hatch and those that were recently laid. This allows you to delay the first cover application to 525 DD, or a delay of 100 DD from the traditional first spray for codling moth control (150 DD is the average length of the egg stage). From 525 DD on you would apply sprays at normal intervals based on residues.

WSU recommends to use this delayed first cover management program:  Apply the first oil at 375 DD, then 150 degree days later put on the first cover at 525 DD.  Then 15 days later (depending on residue length) put on the second cover. This approach leaves only a small percentage of egg hatch at the end of each generation uncovered. An oil-only program requires re-application intervals of 200 DD under low pest pressure and 150 DD under high pest pressure. CM granulovirus is effective when applied at 525 DD and repeated every 5-7 days until about 950 DD (4-5 applications). In any program, mating disruption increases control considerably. In high pressure situations, use CM granulovirus with oil for better control.

The old approach was to time first cover at 425 DD. The problem with this strategy is that residues do not last long enough to protect the crop using 2 applications per generation. Applications at 425 DD miss the first larvae to emerge between 380 DD and 425 DD (missing about 2% of larvae). The second cover spray needed to be applied after 15 days, but the residues would begin to weaken about 15 days later and leave the remaining hatching larvae unaffected (missing about 18% of larvae at the end of the season). These codling moth larvae could then cause fruit damage. Therefore, this approach is inferior to the delayed first cover program described above.


codling moth delayed dormat figures
Delayed first cover timing (right) kills a larger percentage of eggs/larvae then normal timing (left) by limiting the period where residue is weak. Figures courtesy Dr. Vince Jones, WSU Entomology.

Additional Information

What Makes an Effective Codling Moth Management Program?

Decision Aid System


Img1426_pp Vince JonesVincent P. Jones, Professor & Entomologist

Department of Entomology, Washington State University
Tree Fruit Research & Extension Center, Wenatchee, WA


Chambers-Ute_lgUte Chambers, DAS Manager/ Outreach

Department of Entomology, Washington State University
Tree Fruit Research & Extension Center, Wenatchee, WA


Img1380Tianna DuPont, WSU Tree Fruit Extension Specialist

Tree Fruit Research & Extension Center, Wenatchee, WA, (509) 663-8181