OK, I found what I think you are using.
Again I’m not disputing your spray program at all. It’s obviously working for you. I notice the a.i. is permethrin. I use permethrin some, but the professional literature says it offers protection for about a week.
I think the key to the label is that it says it keeps working for “up to” 4 weeks. I could conceivably envision permethrin working up to 4 weeks on some insects under perfect weather conditions. As you know compounds break down at different rates based on sunlight, temp, humidity. And some pests are more tolerant of residues than others.
MSU had a really good chart for residual assays for some major fruit pest (OFM, or possibly CM) not counting rain washoff. I can’t find it right now, but their field assays showed permethrin had lethal activity for about a week. Spintoram was two weeks. I think phosmet was also two weeks. Organophosphates break down fairly quickly, but the rates are so high, there is enough residual to last a long time.
The closest thing I could find was a chart for apple maggot. They show group 3a (i.e. permethrin and other pyrethroids) as a 7 to 10 day residual.
It’s not unusual for manufacturers to pick the most optimistic results for their product chemistries. Triazicide “once and done” claims up to 2 months on the label. But in practice the product residual (gamma cyhalthrin) does not remain lethal for that long for major tree fruit pests.
That said, again, if your program is working for you, no reason to change it.
