Noninfectious Disorders
FIELD GUIDE TO INSECTS AND DISEASES OF ARIZONA AND NEW MEXICO FORESTS
Winter Injury
Figure 286. Figure 286. Needle bases of 1-year needles are green but tips are brown.

There are several different types of winter damage of conifers in the Southwest. Water deficit can develop in dormant evergreens during warm weather in late winter or early spring when needles transpire water from leaves and stems while the soil is cold or frozen. Roots extract insufficient water from cold soil and none from frozen soil. Freeze damage occurs when needles no longer have enough moisture to survive normal nighttime temperatures. Freeze damage can also follow untimely deacclimation from temporary warm weather. Ponderosa pine and alligator juniper are the species most often observed with damage by these phenomena.

Figure 287. Figure 287. Winter injury can be mistaken for mortality at a distance.
Sometimes the result is trees that have needles with brown tips and green bases, and other times trees may have winter-killed needles that are completely brown regardless of age, but the branch and bud tissues are still green and viable. In either case, trees recover during the growing season. Occasionally, severe freeze damage near the upper elevational limits of a particular tree species causes mortality or topkill.

References:  83, 93