Browning, falling needles on pine trees may be a natural occurrence, depending on the species and age of the pine tree. If the inner needles are browning and dropping beginning in autumn, the pine tree may simply be shedding its older needles. This can occur every three to four years in pine trees. If the browning and dropping of the needles isn't a natural occurrence and is happening to the outer needles, your pine tree may be suffering from insect infestations, diseases or environmental stresses. You must first diagnose the root cause of the browning, falling needles before taking the appropriate actions to save the pine tree.
Diagnose the Problem
Determine whether the needle browning and loss is due to drought damage. Needles that turn brown and drop in late summer or early fall, beginning toward the top of the pine tree and spreading downward, is likely due to drought stress.
Detect an infestation of the Southern pine beetle in your pine trees. Look for needles turning from yellow to reddish to brown within one to two months, as well as for yellowish-white tubes of resin that are about ¼- to ½-inch long on the bark and reddish boring dust in bark crevices.
Look for browning, straw-like older needles with healthy, untouched new-growth needles to detect a European pine sawfly infestation. The sawfly larvae resemble caterpillars, are grayish-green and have a lighter-colored stripe down their backs with stripes along each side of the body. The larvae usually feed in groups, with several feeding on the same needle.
Inspect your pine tree's browning, falling needles to look for small white speckles or flecks to detect spider mites. Spider mites may also leave webbing, old skins and eggs on the foliage. Spray the pine tree with a miticide in early spring or fall, when the mites are most active.
Diagnose an infestation of white pine weevils by looking for egg-laying cavities bored into the bark, beginning just below the bud cluster terminal and extending to the terminal shoot. The white pine weevil is a beetle-like insect with a long "snout" and an armored shell. If your pine tree is infested with these weevils, you'll see resin droplets in spring on the previous year's growth.
Look for silky, ¼-inch-long bags containing larvae to spot bagworms infesting your pine tree. You'll see the larvae hatch and emerge in late May or early June, feeding on the pine tree until late August or early September.
Identify Sphaeropsis tip blight in your pine tree by looking for stunted, brown new-growth needles, spreading from the lower branches and upward. To treat your pine tree for this fungal disease, spray the entire pine tree with a fungicide during the third week in April and again in the second week in May.
Treat the Pine Problem
Save your pine tree from drought damage by making small holes in the soil around the tree at the outer ends of the branches that are about ½ inch wide and 6 inches deep. Set a soaker hose over the holes so that the water is directed to soak into the soil, allowing the water to slowly drip for about three to six hours. Repeat this irrigation once every three weeks between May until late August.
Treat your pine tree for a Southern pine beetle infestation by spraying the tree with an insecticide containing lindane or chlorpyrifos until the bark is thoroughly wet. Spray the entire tree, especially the trunk and main branches that have evidence of beetle activity.
Control a European pine sawfly infestation by removing and destroying all infested branches. Spray the entire pine tree with a horticultural oil or insecticidal soap that's labeled for sawflies, applying the treatment ideally in late April or early June when the larvae are newly-hatched.
Control a white pine weevil infestation by spraying the entire tree with an appropriate insecticide, concentrating the chemical application on the upper branches and central trunk. Spray the tree when the adults are most active, either in the spring or fall, because the chemicals will kill only the adults and not the larvae or eggs.
Protect your pine tree from dying due to a bagworm infestation by removing and destroying the silky bag cocoons during winter and spring, before the eggs hatch. Spray the pine tree with Bacillus thurnigiensis, malathion or diazinon during mid- to late June, before the silky bags form.