Hi Will, good guess. Pine needle cast has a different sign at first.
Hi Smoke, I agree with FourMileMarc. It isn't a sign of humic acid overdosage.
Hi Treebeard, you're correct.
Hi FourMileMarc, fungal infection can be seen scatterly on the same shoot.
Hi TimD, if you didn't recognize the problem soon enough, you're in big trouble.
I' ll tell you what I did when I saw this sign on one of my landscape JBP. I cut this shoot and then brown needles removed with help of pick-up. Using a magnifier, I can see some tiny cloudy yellow drops (pic. 1 and 2). Those are pine larvae's feces. They were removed, then a small track was seen. A live larva's head seen in pic. 3. It had a cell extraction with help of pick-up and was seen in pic. 4.
In pic. 5, the dead larva was found on other JBP even though it didn't show any pine borer's activity. I prophylactically sprayed all of my black pine trees with insecticide.
p/s: watch out for another thread which will show you how to approach brown needles
Bonhe