I’ve been successful using triazicide and/or spinosad to stop codling moth. This has worked very well. But I’m concerned about the bugs developing resistance (or rather, a resistant strain of bugs becoming established) and wonder whether it would be wise to switch off either during the season or from year to year.
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I think it’s always considered “best practice” to switch off insecticides to avoid any survivors building up a resistance.
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I think rotating insecticides is a good idea. Insects do develop resistance and rotation is one way to reduce the risk of this happening. It does occur in commercial orchards and that has been studied. No one has studied it in small home orchards as far as I know. The risk should be lower in a small orchard but it’s unclear how much of a risk it is.
I think the best practice would to rotate between sprays or to mix the two insecticides and spray them together. I don’t think spraying with one insecticide one year and another the next year will provide much benefit. Also you would want to use insecticides from different classes just like you do with fungicides. The triazicide/spinosad rotation would work well since these insecticides are in different classes. I was thinking of doing the same rotation next year or replacing the triazicide with the new formulation of Sevin in the rotation since the new Sevin is supposed to work better.
Pyrethroids are the most common class of insecticides used by backyard growers. Both triazicide and the new Sevin (zeta cypermethrin) are in this class. If the insects in your backyard orchard develop a resistance to this class you’re between a rock and hard place since the other options are limited. Rotation is a good way to prevent this from happening.
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Also you may want to look at this article. It talks about spinosad increasing the effectiveness of pyrethroids in populations of insects that are resistant to pyrethroids.
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Very useful, and much appreciated. Thank you!
This contains relevant info…
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Thank you for saying “Thank You” 
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