Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: THURSDAY, November 18, 1993                   TAG: 9311170050
SECTION: CURRENT                    PAGE: NRV-14   EDITION: NEW RIVER VALLEY 
SOURCE: Joe Hunnings
DATELINE:                                 LENGTH: Medium

DON'T LET YOURSELF BE NEEDLED BY YELLOW EVERGREEN FOLIAGE

Because the condition is triggered by weather and season, many evergreens are likely to show symptoms at the same time. If you are not familiar with this phenomenon, you could get concerned.

Each species of evergreen usually keeps its needles for a definite length of time. White pines are the most dramatically affected. This species typically bears three years' needles in summer and two in winter. However, very vigorous leaders or laterals may, by November of any given year, have only one year's needles still attached, and they may not extend all the way back to the first node.

Matured white pine needles turn yellow throughout the tree. The tree will appear particularly unhealthy when these yellowed needles outnumber the green ones of the current season.

Austrian and Scotch pine usually retain needles for three years. Red pine ordinarily drops its needles in the fourth year.

The needles of arborvitae, or white cedar, usually turn brown rather than yellow when they age, and they often remain attached much longer than mature pine needles. Yew needles turn yellow and drop in late spring or early summer of their third year.

Spruce and fir needles also yellow and drop with age; but because these trees retain their needles for several years, needle drop often is not visible unless you really look for it on inner branches.

These are general patterns of needle drop, and you should remember that considerable variation exists from tree to tree and from year to year.

It is important that you do not confuse this natural seasonal needle drop with various disease and insect problems that can seriously reduce the vitality and aesthetic value of the tree.

The facts that it is a seasonal occurrence and that the symptoms are distributed generally throughout the interior portion of the tree are helpful clues to proper diagnosis, but you should examine the needles carefully if there is any doubt.

Needles that yellow and drop from age may have occasional spots and blemishes but nothing more. Old needles sometimes show mottled brown coloration from invasion by saprophytic - nondisease - microorganisms.

Since several fungal diseases in Virginia can cause severe needle discoloration and drop, you should be alert to their possible presence, especially if spots are developing on the current season's needles. Some forms of herbicide injury can also be involved in needle yellowing and drop.

Mites often cause nonseasonal needle drop, particularly of spruce. Generally, needles are off-color, becoming yellowish or brown. A light webbing is associated with heavy infestations. If you suspect mites, hold a sheet of white paper under a branch and tap the branch sharply. The mites will fall to the paper, where they can be seen.

Needle miners of spruce result in clusters of dried, mined needles, usually webbed together. They have also been found affecting several arborvitae in Virginia. Aphids may cause severe yellowing of white pine needles, particularly new needles.

While you can't really do anything about seasonal needle drop, you can do some things to prevent injury to younger foliage and help maintain tree vitality. For instance, it's a good idea to irrigate evergreens thoroughly before the ground freezes to minimize the possibility of winter injury through desiccation. Also, examine your ornamental evergreens periodically for evidence of insect and disease problems.