Thank you for contacting Ask Extension. Could you give me a bit more information about the pine trees? I need pictures of the entire tree, one of the base, and if all 4 are planted in the same area, one of all of them together. 

Also, are the trees in full sun or shade? How old are they and when planted? Does the soil drain well or does water stand for a while? Are they planted on a hill, valley, near water or near a house? Is this the first year you have seen this?

Once I receive this information, I can better access the problem.

Thank you for contacting Ask Extension. Thank you for the additional pictures and information that you sent. It would appear that the potential cause of the leader dieback is the presence of white pine weevils, which can feed on the sapwood of the leaders and cause the tree to become bushy. It is indicative of a shepherd’s hook-like on the leader of the tree. The first symptoms are pearl white resin on the leaders, which I do see in the picture you sent. The leader dies when the branch is girdled as the adults emerge.

The adult weevils overwinter on the ground. Once they warm up, the weevils move up to the tops of the trees in late afternoon or early evening and feed on the terminal leader. Each time a female weevil makes a feeding wound on the terminal, she lays one to four eggs in the wound. Those eggs will hatch within a few weeks and the larvae chew their way through the bark. They will feed in the phloem under the bark for several weeks, pupate and then emerge as new adults around mid-summer.

You can control by pruning out the infested leaders before mid-July and burn or put in plastic bad and throw away these branches to kill the insects within. After removing the leader, prune back all but one remaining side shoot by at least half their length. This will allow the remaining (unpruned) shoot to replace the infested leader that was removed. If you prune before the holes appear on the leader, then you can reduce the amount of adults that will lay eggs next year.

Spraying with Sevin is a step in the right direction, but it is the wrong time of year to spray the weevil to be effective. Spraying in early spring is the best time to kill the pine weevils. About late March is when you want to spray the leaders that are now the top of the trees. You want to kill the adults before they can begin to lay eggs.

***So, since it is too late to spray anything to be effective, you should prune out the infected leaders on any of the pines that have sap running, indicative of the white resin. Throw these branches out or burn them, because they do have the live weevil inside. Since they are turning brown, they are girdled and you can do nothing for them at this point. You want to save the trees. Prune the other branches to form a new leader, I have included a publication on how to prune an evergreen for your reference. This will help reduce the amount of adult weevils. Then in the spring, around late March, early April, spray with a pyrethrin insecticide. It is imperative that you only spray the leader so as not to harm birds and pollinators that use the tree.

If the problem persists, it would be advisable to have a certified arborist inspect the trees to accurately diagnose the issue and recommend a course of action. This is particularly important as the trees are still young and may be more susceptible to stress and pest damage. www.treesaregood.com

Here are some publications to help you with the pruning and how and what to spray:

https://blogs.cornell.edu/treeipm/2013/07/08/white-pine-weevil/

https://www.canr.msu.edu/news/control_white_pine_weevil_in_early_spring

https://www.pubs.ext.vt.edu/430/430-457/430-457.html