Codling moth management decision-making - Part III: Second generation

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

In this follow-up to the early season codling moth (CM) management articles, we focus on monitoring and control of the second generation. As always, emphasis should be placed on the use of pheromone traps to monitor CM activity and assess pest pressure in specific orchards. An unusually cool spring and summer have substantially impacted CM populations in the state. Most adult activity, i.e. mating and egg laying, takes place over a period of three to four hours beginning at dusk, and moths are essentially inactive at temperatures below 60°F. Thus, it is not surprising that first generation CM pressure was unusually low in many orchards, and growers who based spray decisions on monitoring information from their farms were able to save money by eliminating unnecessary control applications. We are aware of several growers, especially if they applied mating disruption, which did not have to apply an insecticide for first generation CM control. To get the most benefit from the reduced CM activity that is the rule rather than the exception this year, growers should treat an orchard only after significant moth captures have been recorded and the accumulation of growing degree days (GDD) required for a particular action has taken place.

The vast majority of insecticides used for summer CM control are aimed at killing larvae. Options for controlling CM larvae include conventional contact poisons, like the organophosphate (OP) compounds, Guthion and Imidan, and a number of pyrethroid insecticides. These materials primarily target newly emerging larvae, and thus are typically applied beginning at the start of second generation egg hatch. The CM model predicts this will occur around 1,250 GDD after the initial biofix was set in May. However, the actual onset of second generation egg hatch is highly dependent on when (and if) the fruit were infested in a particular orchard by first generation larvae. Thus, the best way to predict egg hatch is to calculate the GDD’s after the first consistent catch of second generation moths in pheromone traps. Egg hatch will start following the accumulation of 250 GDD after second generation moth activity is detected. Pyrethroid insecticides appear to be less effective in the summer for second generation CM compared to early season use for first generation control. Apple growers also should be aware that resistance to the OP compounds has been detected in Michigan orchards throughout the state, most extensively in the Fruit Ridge and Southwest production areas. The levels of resistance detected were high enough in those orchards that sole reliance on OP’s for CM control is not likely to provide sufficient control. In addition, populations resistant to OP compounds may also be resistant to pyrethroids.

Several new materials have become available for CM larval control and growers are encouraged to include these new products in their CM management programs. Integrating them into CM management programs will not only improve CM control in orchards experiencing problems, but also will help delay the development of CM resistance to OP’s in locations not yet experiencing control failures. The newest options for CM control are three compounds that received their US EPA registration in 2008: Delegate, Altacor and Belt. Delegate and Altacor were commercially available and widely used in 2008, while Belt was registered late in the season and is essentially commercially available for the first time this season. Good resistance management should be practiced in choosing a material for second generation CM control. Doing so entails NOT using the same compound or class of compound that was applied for first generation control.

Delegate (spinetoram) is a new compound in the same insecticide class as SpinTor (spinosad). A major difference between the two spinosyn compounds however, is that spinetoram is much more lethal to codling moth larvae. In small-plot and on-farm trials, Delegate has provided excellent control of second generation CM. It has excellent residual activity, providing control for at least 14 days. Delegate kills larvae as they hatch and begin feeding, thus should be applied at the egg hatch timing of 250 GDD after a significant moth catch is recorded. Delegate also has very good activity against summer generation obliquebanded leafrollers. Although also active against apple maggot, results of small-plot trials have been mixed and more research is needed to determine the level of AM control Delegate will provide.

Altacor (rynaxypyr) belongs to a new class of Diamide insecticides that work on the insect by activating ryanodine receptors, thus depleting internal calcium and preventing muscle contraction. In small-plot and on-farm trials, Altacor has provided excellent control of second generation CM. Although Altacor has some ovicidal activity it is primarily a larvacide and thus, Michigan apple growers should apply this product at the egg hatch timings. Altacor provides excellent obliquebanded leafroller control, but has limited activity on apple maggot.

Belt (flubendiamide) is a new Diamide compound with the same mode of action as Altacor. Belt also has provided effective control of second generation CM and should be applied at the larvacidal timings discussed above. Keep in mind however, that if either Belt or Altacor were used to control the first generation, neither compound should be used for second-generation control. Belt also provides excellent obliquebanded leafroller and Oriental fruit moth control and appears to be relatively safe on most beneficials.

The neonicotinoids, Assail and Calypso, will provide very good control of CM with a residual action of 10 to 14 days. Proper timing and coverage is required to achieve control. These compounds are primarily larvicidal, but also have some ovicidal activity when applied over the top of the egg. Assail is labeled for CM control at the rate of six to eight ounces per acre, but the high rate has shown better performance, especially for second generation CM. Application rates near the high end of the label rate are also recommended for Calypso, especially where CM densities are high or for prolonged control. Field trials have indicated that use of Assail in combination with pyrethroids or carbaryl can result in outbreaks of phytophagous mites. Assail and Calypso are fairly broad-spectrum materials. The major secondary targets of these neonicotinoids are aphids and leafhoppers. Additionally, applications targeting second generation CM will also provide apple maggot control.

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