This looks like normal needle drop on your lodgepole pine, possibly more than normal because of transplant shock.  I don't see any signs of disease or insect damage on the needles, and, most importantly, the needles on the ends of the branches are green and healthy.  If insects or disease were causing needle drop you would see it in all parts of the tree.  This article gives additional information, Autumn Yellowing of Conifer Needles  https://csfs.colostate.edu/2016/09/13/autumn-yellowing-conifer-needles-normal-process/. 

You've been very  diligent in watering your tree.  That's very important for this tree for two reasons;  1.  the tree has only recently been planted so the roots haven't grown into their new home and the tree hasn't yet established itself, and 2.  we've had a very hot dry summer with prolonged heat waves.  This makes it very difficult to keep our plants hydrated.

The donut bag is a great way to water.  It holds 14 gallons of water which is great, is measured and releases the water over time.  I agree about hand watering in that it's difficult to measure.  You can also use soaker hoses looped around the tree. 

Hello Deb

Thank you for your response.

I don't think this is dothistroma needle blight because:   the tree as a whole looks very healthy, there's no sign of lesions on the other needles, and needles affected by dothistroma are green at the base and your shed and attached needles are all evenly colored.  This article discusses this disease in our area, Dothistoma needle blight  https://pnwhandbooks.org/node/3276/print.  This article has a good discussion and good pictures of affected trees and needles, Dothistroma Needle Blight in Pines  http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/needlecasts/dothistroma-blight.aspx..

I do see the spots on the needles, though,  and am going to reassign this to someone with more expertise on tree diseases.