This model counts accumulated rain and number of days from last spray to estimate when residual coverage will begin losing ability to kill codling moth larvae before they penetrate apples.
Codling moth does not normally require specific attention in New England orchards where full block insecticide applications are made to prevent European apple sawfly and plum curculio damage. While those applications are not ideally timed for control of codling moth larvae, experience shows that their effect on adult, egg and larval codling moth is enough to prevent noticeable codling damage.
However, where alternative measures such as perimeter sprays or Surround are used for plum curculio, adequate secondary control of codling moth may be lost. The purpose of the codling moth insecticidal control model is to indicate how insecticide application dates and expected residual efficacy depletion dates line up with codling moth egg hatch. This information is particularly important for organic growers who have only Surround, Bt and Entrust for codling moth control options. Using these materials efficiently and effectively requires knowing when to start applications and how long to continue coverage.
The Orchard Radar Codling moth model applies generally accepted "rules of thumb" for how long a given full-dose application will last before losing their effectiveness due to time, rainfall, ultraviolet light, tissue growth and other influences.
Two sets of rules are used to estimate depletion of effective control from a full dose insecticide application. The first set evolved over many years for Imidan and Guthion (azinphosmethyl). After discussion with manufacturer representatives for Avaunt and Assail, these rules are also applied for those products. For all of these materials, excellent coverage is essential for codling moth control. This may be even more important for the Assail and Avaunt, which may have less redistribution with subsequent rainfall than Imidan or Guthion. Lacking information to the contrary, these rules seem to be the best available for Actara, Calypso and pyrethroids.
Residual protection from previous full-dose Imidan, Guthion,
Avaunt or Assail application is considered depleted when one of the
following conditions is met:
checking with product labels, a second set of rules was adapted for Bt
insecticides (e.g. Agree, Dipel, Javelin, MVP, Xentari) and Entrust. These
materials provide shorter effective residual codling moth control, and they are
considered depleted when one of the following conditions is met:
Egg hatch percentages are based on "Codling moth control - A new tool for timing sprays", Jay F. Brunner, S.C. Hoyt, M. Anthony Wright. Washington State University Extension Bulletin 1072, 1987.
Using the model
Find the date of the previous insecticide application. Then find the 'end of protection date' column on that same row for the type of insecticide used. The table shows the estimated percent cumulative codling moth hatch on that date. If the egg hatch value is considerably below 100%, then a follow-up application would be needed to provide additional protection to account for a larger portion of codling moth egg hatch. Heavy rains shorten the effective protection intervals.
For Bt and Entrust, the model indicates that it will take 3-4 applications to provide protection from 3% egg hatch until 90+% of first generation codling moth egg hatch has been completed.