Perhaps you could post a photo of it? Are the needles of the newest (this years) growth also turning brown and falling off?
Pinus Taeda should be able to handle the heat just fine is it is a warmer climate conifer. Could it be drought stress? Perhaps it did not get the same water as the others? Or, Many pines (some much more than others) do a considerable needle drop in fall, but usually that is it shedding its oldest needles. Anything else look off?

Has every needle turned brown and fallen off or almost every needle, meaning there are still some on it that are green?
How much and how often have you watered them?