Old needles inside the canopy give out on a schedule. Yellowing evergreen needles in that inner band are most often normal seasonal drop, not a sick plant, and you can confirm that from the driveway. Look at the ends of the branches. If this year's tip growth is still green while the yellow sits behind that new growth, your tree is dropping old needles right on time. Real trouble runs the other way. Trouble shows up on the newest needles first.
A row of white pines along my own gravel driveway went yellow through the middle one October, deep enough that I could see the color from the road. The tips stayed green. I checked the band on every tree in the row, and the yellow sat the same distance in from the branch ends on all of them. Within three weeks most of that yellow was lying on the gravel instead of hanging on the trees.
One check settles most cases for you. Look at where the yellow sits, not at how much you see. Interior needle drop shows on the older needles behind the tips, and the color runs through the inside of the plant in an even pattern. University of Georgia Extension describes old needles yellowing top to bottom while the newer tip needles hold their green. When this season's growth at the branch ends is the part turning, you are looking at insects, disease or herbicide instead.
The spread matters as much as the color. Normal drop shows through the interior portion of the plant, on the shaded needles closest to the trunk, and you see a wide band rather than a patch. Walk around your plant and look from three or four angles. Seasonal drop looks the same from every one of those angles.
Spruce is the plant to watch closest. Mites leave a stippled, dusty look on the needles with light webbing between them. Needle miners work inside spruce and arborvitae needles, where you cannot spot the damage from a step away, so hold a branch up close. New white pine growth that goes hard yellow points you to aphids. Weed killer counts too, whether the spray drifted onto your low branches or soaked in near the roots.
Color throws people off. An evergreen turning brown instead of yellow is not in worse shape by default. Arborvitae needles brown as they age rather than yellow, and those needles stay attached far longer than matured pine needles do. So a brown interior on your arborvitae can sit in plain view for weeks while the plant is fine. Each species sheds on a different timetable, and the main guide walks you through that schedule plant by plant.
Start at the branch tips before you buy anything. Green, firm tips with yellow behind them need no treatment at all, and your only job is raking up what falls. If the new growth is the part going yellow, turn a branch over and check the needle undersides for mites or aphids. Then think back on any weed killer you used near the roots this year. Check your drainage as well, since soggy ground and long dry spells both push needles off out of season. Call your county extension office when yellowing evergreen needles keep showing on this season's tip growth.
Photograph the branch tips today, then take the same photo two weeks from now. Green new growth in both shots tells you the yellow behind it is the normal cycle and needs no spray.
Read the full article: Evergreen Trees: 8 Types and How to Choose
