Chemical Control

Considerations for Effective Applications

By Vincent P. Jones, WSU Decision Aid System. Updated May 1, 2020.

Without any intervention, codling moth numbers increase about four-fold from generation to generation. Therefore, targeting the first generation is important to reset the population size to a minimum. Control measures for subsequent generations can be adjusted to the local pest pressure indicated by trap counts.

What’s in the pest control toolbox?

The targets for pest management are the adults, eggs, and neonate larvae which are affected by mating disruption, ovicides, and larvicides, respectively. The combination of these three tools has proven most effective in keeping fruit damage below the economic threshold.

Mating disruption is the first line of defense – it delays and prevents mating and egg laying. Mating disruption dispensers need to be in place by roughly 100 DD or bloom, before the first adults emerge at 175 DD; these typically last all season long. Mating disruption is particularly effective as the temperatures increase and will dramatically improve the activity of pesticides applied during the season.

Ovicides are the second line of defense. Eggs can be prevented from hatching with topical or residual pesticides. Oil is a preferred option; it suffocates the eggs that have been laid. Its residue is short – only about 1 day, however, because it kills eggs that have already been laid, it has an effective residue of 150 DD (the length of the egg stage).  This is extremely important because it makes oil applications very effective in the early spring compared to the codling moth granulosis virus (discussed below). Oil also tends have a relatively minor effect on natural enemies so it is compatible with Trichogramma parasitoids that have been shown to help suppress codling moth populations by attacking the egg stage.

The third line of defense is larvicides, such as conventional larvicides or codling moth granulosis virus. Both target the newly hatched codling moth larvae which almost immediately bore into the fruit. Therefore, precise application timing is important, because once larvae enter the fruit, they are protected from pesticides. Granulosis virus has a relatively short residual activity (5-7 days), so it is best used in the second generation.  Conventional insecticides tend to be active from 12-17 days, so residual activity period is not so sensitive as with the granulosis virus.

What’s the best insecticide application timing?

In conventionally treated orchards, the delayed first cover strategy is the best management strategy. This program uses an oil applied at 375 DD to prevent any eggs that have already been laid by that time from hatching. This means that, after this oil application, no newly laid eggs will hatch for another 150 DD (duration of the egg stage). This allows the first larvicide cover spray to be delayed by 150 DD until 525 DD. At that point, the larvicide with its longer residue is active during the majority of the egg hatch period. A second larvicide cover spray is timed depending on the pesticide’s residual activity period. For conventional programs, it is typically about 14 days (see table). So, overall, only the oil spray and two additional sprays would normally be needed to control the first codling moth generation.  Sampling at the end of the generation gives a good indication of the efficacy of the program and the need to treat later generations.  In many situations, if you are using mating disruption, and the population was under control the previous year, you may not need the second cover spray unless migration from untreated areas occurs.

Organic programs should always use mating disruption, without it, codling moth control is extraordinarily difficult.  Compared to the conventional application timings, organic timings are slightly different in that the residue of granulosis virus is fairly short (5-7 days) and during the first generation it is rare that the residue gives as good a control as oil alone. The application of oil at 375 DD, should be followed by 2-3 more applications of oil at 150 DD intervals during the first generation. As with the conventional program, sampling at the end of the generation gives a good indication of the efficacy of the program and the need to treat later generations.

Whether the second and third codling moth generations require additional insecticide applications depends on the pest pressure. It is not always necessary to treat every generation to prevent damage. Remember, mating disruption is still active and keeps reducing the number of eggs laid, which in turn reduces the need for supplemental sprays. Careful monitoring of adult flight with pheromone traps, larval sampling at the end of each generation, and knowledge about potential infestation sources (such as bins or nearby untreated areas), are essential in determining when treatments are really needed. And even if traps show an unexpected increase in numbers in the next generation, a well-timed intervention will knock down the population again.

If sprays are required in organic orchards in the second generation, a oil only treatment program (as used in the first generation) is not recommended because excessive oil applications can reduce tree vigor. In this case, the residue of virus during the summer gives good control of codling moth larvae when used with a delayed first cover program.

The time of year also plays a role in pest pressure. After August 20th, all newly-hatched larvae are destined for diapause because of changes in day length. While those larvae still pose a risk for damage and may need supplemental pesticide application, they will not complete development this year into adults that could lay more eggs. Instead, they will enter the pool of diapausing codling moth that will emerge next spring.

As a general goal, the number of larvae reaching the overwintering stage should be kept as low as possible. The occurrence of a full fourth generation of codling moth, as occurred in 2015, adds more diapausing larvae to the overwintering population unless orchards are protected. Low overwintering numbers, however, lay a good foundation for soft and low-input programs in the following year. Always expect higher codling moth pressure the year following the occurrence of three or more generations of codling moth adults.

Management strategies and timing for codling moth control. Mating disruption should always be used.

Management Strategy	Sprays per CM Generation	Spray Timing
Conventional Delayed First Cover	3	1st spray: oil just before egg hatch (375 DD)* 2nd spray: larvicide at 525 DD (“delayed”) 3rd spray: larvicide 14 days after 2nd spray
Organic oil Only in first generation	3	1st spray: oil just before egg hatch (375 DD)** 2nd spray: oil at 525 DD 3rd spray: oil at 675 DD
Organic Delayed First Cover, virus (only if needed based on scouting and only in second or later generations)	4	1st spray: oil just before egg hatch (1375 DD)*** 2nd spray: virus at 1525 DD (“delayed”) 3rd spray: virus 7 days after 2nd spray 4th spray: virus 7 days after 3rd spray

*For second generation treatments based on need: add 1000 DD to timings above for each generation treated after the first generation.

**Do not use an oil only program in generations after the first.

***For third generation treatments: add 1000 DD to timings above; do not use this program in the first generation.

Having problems with your codling moth control?

If you have had problems with codling moth and have not seen efficacy with oil alone or oil + a pesticide applied multiple times, check your timing on the WSU pesticide effects web site (https://pesticides.decisionaid.systems). To use the web site, select the closest weather station to your orchard, choose the year, and input the timings of your insecticide applications. The models will tell you the importance of each spray and the overall effects of mating disruption and the relative efficacy of your spray program over the entire season. The tool also provides guidance about optimal control programs for each of seven different pests (including codling moth).  If the tool shows your timing is close to optimum, but you had bad results, it is almost surely a result of poor spray coverage, especially when oil is used. Oils, in particular, require good coverage, because the oil physically coats the eggs and prevents oxygen from reaching the embryonic larva. Because this is a physical coating, it is not something that the insect can develop resistance to – this means the only likely problem is poor spray coverage.

Spray coverage is critical and cannot be achieved at low gallonages and high tractor speeds. In general, oil requires a 1% solution and needs to be applied in 100-200 gallons per acre (depending on tree size). Speeds over 2.5 miles per hour are not recommended. Use water-sensitive spray cards clipped to the leaves to evaluate your spray coverage.

Additional Resources

For specific timings view the Decision Aid Systems

To test your application timings use this tool: Pesticide Effects Model

For a listing of codling moth materials see our page Codling Moth