In the communities who consider such things, broad spectrum spraying has lost the 'green revolution' cache of the '50's  '60's and '70's.   Bio-accumulation of constituent metals etc in soil; effects on non-target species-vertebrate and invertebrate; neurotoxicity to humans sorts and critters; mis-application, in terms of timing for specific 'bug', virus, or bacteria or consideration of climatic conditions, wind drift, rain, too much sun during application, overspray' all contribute to the consideration.

The alternatives are usually probably going to involve a very much hands on approach and analysis of what you are dealing with.

Well established orchard acreage, standard trees, or one of two trees on small rootstocks. New plantings.

What's causing the curl? Stone fruits generally seem to be at risk here for rain born dis-eases; choosing resistant varieties if planting new is a strategy. If Bacterial infections , some people are finding success with a beneficial bacterial, compost tea, applied to out compete the opportunistic bad guys. Others can speak to that with some experience.   I've stopped pruning my stone fruits in the dormant (wet here) season and concentrate on summer pruning. Maybe the winter and spring have been favorable for me for the last 5 years. Since I stopped pruning stone fruit any where near rainy season I've not had what I was calling a "peach leaf curl like" phenomenon on my ume plums (maybe related to apricot). This year I thought it had returned, was fortunate to have a better set of eyes visit, who noted it was shot hole disease that is going on there now. Clipping and disposal of the affected areas, twigs, buds, leaf areas is recommended, hygiene.  I'm keeping most of my trees small so I can reach easily, probably will prune to a more open canopy, for air/light circulation.

    What are the offending critters, when do they arrive; practicality of trapping or pheromone lures to confuse mating, regeneration cycles. There is no-cost computer modeling program, counting of the degree days to calculate the stage of development of insect specific- dialed in to your specific location for effective timing of control methods. Available at uspest.org  supporting integrated pest management know as IPM. Tonia, at the HOS arboretum uses this modeling to apply a virus specific to the coddling moth larva, (OMRI acceptance) for apples and pears.

 I am concentrating on hygiene practices for insects, keeping fallen fruit picked up and disposed of before larva can migrate into the ground; and sticky traps with lures on my apples for apple maggot fly. Populations have gone down notably over a few years. You can try 7 or 10" cardboard collars for traps, wrapping the trunk 6 to 12" above grade, some larva may hide out in the corrugations, dispose and replace if populated. Earwig houses, earwigs eat aphid as do ladybug larva especially, and praying mantis. Humming birds eat coddling moth. Put out feeders.

I might try some neem oil for the shothole on my ume plums; I'll probably procrastinate to see if the ume out grow it this year. Maybe look seriously into brewing compost tea; I've been exposed on a couple different levels more and less sophisticated. I'd probably opt for the less sophisticated 5 gallon bucket and aquarium aerator (and heater?) setup. I think foliar feeding with seaweed extract would be beneficial to feed and strengthen the trees immune system. 

AND what is an acceptable amount of damage. I don't do much except prune and pick up down fruit; and traps in my apples,  cut around the declining number of worms  including those in the pears next door.

If you're making hard cider, most(? needs confirmation) home ciderists, don't worry too much about some bugs except for the very worst of the fruit.    If your making sweet cider, some say that, (ok... me) it makes the cider taste like cinnamon.                 

The spotted wing fruit fly, seems to be attracted to the same kind of homemade apple cider vinegar/molasses/dishsoap sometimes ammonia, traps that regular fruit flies are attracted to. 

This is not by any means all inclusive of approaches, bagging fruit (apples usually) when you thin the crop (soon); there are bio-dynamic preparations and paste remedies for what ails you. But, that's all I got.

In the summer around the emergence of apple maggot fly, some folks will mix up 'Surround'; a kaolin clay product. It acts as a physical barrier, a desiccant, not unlike diatomaceous earth. Works by scratching and causing the contacted critter to lose their fluids. Needs to be reapplied after rainwash.

I'll use Tanglefoot or Tangletree (glue) on red apple look alikes, and attached attractant lures, hung in my few fruit trees, for apple maggot.

Research whatever you decide to do.

I hate spraying but I admit I do it sometimes when the problems get really out of control.  I have an orchard with about 80-100 trees among them apples, pears, plums, peaches, apricots, citrus, avocado, guava, soursop, mango, persimmon and soon to be added quince.  Obviously mine are low chill varieties.  Since I work from home I regularly take breaks from my home office and walk outside and inspect my trees.  The apples predictably have soft bodied insect problems.  But if they are moderate in number and if I see the lady bugs and their larval stage buggers roaming around the trees doing their thing I leave well enough alone.  The other day one of my Orleans Reinette apple trees got a really bad infestation of mealy bugs.  I could see over the course of a week that it was getting worse even with the presence of ladybugs.  So I brought out the big guns (Sevin) and did a spray of only those trees.  It took care of the pests but it also wiped out the good bugs.  Not happy about that but I had to do it.  The larval stage of the lady bugs are freaking awesome.  Those things are voracious and they never stop feeding except when they are getting ready to molt.  My guava supreme tree had a bad white fly problem until the larval ladybugs showed up.  Now I can't find a single leaf with a living pest on it.  There is plenty of carcasses left behind but the bad insects are very much reduced.  One of my local nurseries will actually sell cartons of lady beetles that are grown in the lab.  The idea is you take them home and release them in your yard.  Some will fly away others will stay.  I did that a couple of time but unfortunately when you have that many good insects around then the frogs decide they want to come out and play (eat) with them.   So you get an explosion of the little frogs in your trees.  They in turn bring in the snakes that feed on them.  I hate snakes but I really don't like to kill anything.  Most of our snakes are non-venemous black racers but we have have cotton mouth around. Most of those guys stay near bodies of water like lakes or canals.   I do have one canal running behind my property but so far I have not encountered a cotton mouth in my yard and I hope I never will.  They are positively scary and very aggressive.  One thing you learn when managing an orchard is how well balanced the food web is in nature.  When left to its own devices mother nature will take care of everything.  Unfortunately human activity often destroys that natural balance and then we have to deal with the aftermath of the damage we caused.