Kym, there are a number of beetles which could be the culprit. But let's back up a minute: So, you cut down some affected trees, right? That's good. But are the remaining trees being obviously affected in some fashion? Or are you intending a preemptive strike? Either answer has value, I'm just trying to figure out what's going on.

The trees that are left have some damage too. Mostly at the bottoms and on the sides where they are up against other trees. I was hoping we could save the ones we left. Those left that have damage look like blue spruce, and there are several healthy Austrian pines (tho I did see what looked like beetle holes on a few of their limbs). I'm really hoping I've misdiagnosed them having pine beetles, because from googling it looks difficult to treat. They seem to mostly be dying from the bottom up.

I do plan on trimming off every bit of dead we left as soon as possible.

Also, I did study up a bit on spruce cytospora and it seemed to fit with what I'm seeing... That is, other than the little bore holes. Another little detail (that maybe isn't worth anything) is that these trees were heavily covered with wild cucumber vine when we bought the place. I did pick the bark off on what I thought was a bore hole on one of the Austrian pines and there was no tunnel underneath. I know almost nothing about trees so I'm just throwing these bits of info out here!;)

Are they bore holes or sapsucker/woodpecker holes? ie. fairly random vs. ordered distribution.

Good job on laying this out! So...first things first: The die-back of lower limbs on the Colorado spruce is almost surely Cytospora. Good catch, and that's a tough one to deal with. In fact, I would say that beyond removing-and preferably burning-any affected branches, there's not much reasonable to be done about that one. Secondly, if you have Austrian pines-and your general location matters here-it may also not be worth the trouble to try to maintain these. They are on my short list of conifers that used to be okay in my area, but which are simply not worth planting anymore due to a duo or trio of fungal pathogens that have ganged up on them in recent years.
Smivies brings up a good point-larger holes and holes in horizontal rows on the trunk are sapsucker damage. Usually not a big deal.

OK so another point" Most of these conifers are at their best in pretty close to full sun. As they and their neighbors have grown, it is inevitable that some shading of lower limbs has occurred. That could account for some of what you're seeing. Not so much in the spruce-that's likely to be Cytospora, but in the others.

If you could, give us your general area. And whereas I've often used pesticides to meet a predetermined goal, this so far does not sound like such a case. Any chance of a photo or two? It may be that these trees are simply becoming overcrowded, in addition to the likely pathogenic items we've discussed already. One thing for sure-I can make no recommendation of any pesticide with the info at hand. We need specific targets before we go there. But it could also be that some cleanup work followed by good general care can improve some of these plants. It is also possible that many or even most of them have reached the end of their useful lifespans. When this happens, then the fun begins because we get to plant new trees! And you are certainly welcome to seek input on that as well.

^ A picture of one of the holes, sorry I couldn't get a clear picture!

We are in SW IA. Could those holes have been made by some kind of bug after the limb died off? The holes are quite random, but some branches have 3 or 4 within a few inches. I didn't notice any on branches that still have life.

Yes, very possible. There are a number of beetles that attack live conifers...but there are also lots that opportunistically eat them when they are dead.

My parents used to have Austrian pine. They developed problems with turpentine beetles. My parents kept them alive with some very expensive spraying. When my parents finally figured it wasn't worth the cost and stopped, they ALL died. (The pines, not the parents).

Look up turpentine beetles and Southern Bark Beetle.
They can kill a sick tree directly, or carry either fungus or nematode to infect a tree. (The way mosquitoes carry malaria to humans).
They can directly kill a weakened tree...but an otherwise healthy one may be able to survive...*IF* your local beetles don't carry disease.
Look for holes with orangish pitch coming out of them.

Except...did you say the Austrian pine were the healthy ones?

Anyway, those don't usually bother blue spruce. Blue spruce are bothered by a host of other problems including Spruce spider mites and general sensitivity to humidity levels. Usually don't manifest as holes in the bark.

Also keep in mind...shaded branches naturally die in most conifer species. It's not a bug, it's a feature.

Carefully identify the species, and see if you can figure out what species are doing well...then plant more of those as "understudies". Plant a second backup windbreak behind the current one, if you have space. Hopefully you can keep the current trees alive long enough for the new windbreak to become a decent size.

Another attempt at a photo of the holes...

yes, so far the Austrian pines look relatively healthy, but I did read they're no longer recommended for IA. I'm disappointed about that because I really like them.

I think that's a good idea to plant a backup windbreak.

Doesn't look like typical bark beetle holes. Turpentine beetles usually don't go for twigs, only trunks...

Any sign of trees bleeding sap?

Think the bark beetles are a red herring. Your problem is a combination of the tendency of trees to lose branches that are shaded an the fact that blue spruce do badly in many areas.

OK, so those holes could have happened prior to branch death...or after. But what I'm mostly seeing is lower branch die-off due to shading, which is completely normal for these sun-lovers. Another thing that I "think" was being shown in some of the photos is the normal tendency for conifers to have lots of "dead" stuff on the inside of the plant. That is, say you were to look at an apparently perfect spruce tree. Now walk underneath the plant and look up. Not a pretty sight is it? All of that dead twiggage and so on is again just the normal dying off of inner, shaded structures. Not at all a sign of trouble.

But here's the thing: IF it's a windbreak you want-and they are good things out in the prairie-you need plants that can handle the conditions. Increasingly, Colorado spruce is not making the grade here. Likewise for Austrian pine. You can't beat this either, excepting by heroic measures which would still ultimately fail as soon as you stopped. I would make one suggestion: If you have space, and by space, I mean an area of sufficient size and one getting close to full sun, plant some Norway spruce. These will grow fast, live long, hold their branches right down to the ground (if not too crowded) and are proving to be the best spruce species for a vast swath of eastern N. America, including Iowa. We could get fancier-and maybe someone here will chime in with some relatively rare pine species. I believe that Bosnian pine, although fairly rare in the marketplace, may be proving to be a better choice for this region as well. What I'm saying is, if this planting consists largely of two hugely problematic species, it may be time to cut your losses and get something good going for the future.

Norway Spruce are fast growing, relatively long lived, good in wind, attractive, and a bit less prone to losing their lower branches then pine or blue spruce. A perfectly good choice. Whatever killed your blue spruce may or may not affect them (since they are a spruce and we aren't 100% sure what disease your blue spruce have) but the Norway Spruce are likely to be more resistant.

White pine (pinus strobus) are highly resistant to both bark beetles and spruce diseases and fast growing, but lose lower branches. (A problem for windbreaks)

Arborvitae are a bit boring to me, but are least likely to show dead
spots in shade and are afflicted by a completely different range of
diseases.

If your windbreak works now, you may have time to plant something relatively slow growing as the back up.

Eastern Red Cedar is super resistant to everything and can form a solid wall, but does show dead spots in shade and is slow growing. Berries birds like but not super attractive.

I like American Holly (ilex opaca) as an attractive windbreak...shade tolerant so fewer "dead spots", birds like it, prunable, afflicted by a completely different diseases....nothing eating your pine will find them appetizing. I've always liked the idea of pairing them with white pine...Unfortunately, really slow growing and would only work in the warmest parts of IA. An option for an optimist in southern IA. What is your USDA zone?

Thank-you all for your help! We will def start thinking about planting a new windbreak. I'll check out the Norway spruce. We are in zone 5a I believe.