Recently we noticed that one of our evergreen trees has a lot of needles that are turning yellowish brown and dropping off. I would say about 25% of the needles are affected, some in the middle of the branches, some at the ends. The needles are about 3 1/2 inches long and are in bunches of five – I think it is a pine.
Is this normal for that type of tree? Or is it more likely the tree is stressed for some reason and we need to deal with it?
This will be a lengthy answer and I will assume you live in the Pacific Northwest—the following information will not apply to other areas.
In order to get an accurate diagnosis you will need to take a sample of your plant (including both healthy and affected parts if possible) to a Master Gardener clinic.
Meanwhile, to learn about diseases common to pines in the Pacific Northwest, go to the Pacific Northwest Plant Disease Management Handbook and search using the term pine. There are several possibilities with good photos. Remedies are included with each disease.
Insect information is more difficult to get, so following are the most likely-sounding pests:
1. Pine (Pinus) – Black pineleaf scale (Nuculaspis californica)
Pest description and crop damage
Mature scales are almost circular, 1/16 inch in diameter, and yellowish brown to black. Young hatch in spring and
summer. Scale feeding is restricted to the needles and results in their becoming splotched with yellow patches. Heavy infestations cause premature needle drop and may result in death of the tree. Affected trees often display a thin crown, yellow or reddish coloration, and a shortening of the needles. This insect attacks various species of pine, ponderosa most commonly, as well as Douglas-fir and hemlock.
Biology and life history
This scale overwinters as an immature. The crawlers start to disperse to fresh foliage in spring. There may be one to three generations per year.
Management-cultural control
Trees under stress tend to be particularly susceptible to attack, as are trees growing in dusty conditions. Avoid creating these types of conditions.
Management-chemical control (home)
Dormant season:
Apply with enough water to cover the entire tree thoroughly.
1. horticultural oil. Apply during delayed-dormant period.
Growing season:
insecticidal soap
2. Pine (Pinus) – Eriophyid mites (Trisetacus spp.)
Pest description and crop damage
Eriophyid mites are tiny, wormlike, whitish or tan mites which feed under bud scales or in the needle sheaths, often
between the needle bases. Symptoms of eriophyid mite infestations include yellowing, distortion, and stunting of new needles, and development of numerous buds where a bud has been infested (rosetting). Severe infestations
may kill needles and cause needle drop, leaving naked branch tips. Rosettes may develop into witches’ broom growths. Two-needle pines, particularly lodgepole or shore pine, are affected.
Management-cultural control
Prune out heavily infested growths.
3. Pine (Pinus) – European pine shoot moth (Rhyacionia buoliana)
Pest description and crop damage
Adult moths are reddish-orange with silver markings on the wings. The mature larvae are about 5/8 inch long and
reddish-brown with black heads. The larvae of the European pine shoot moth feed on tips of branches, boring first into needles or bud bases, then into the shoots. Infested tips are covered with pitch-covered webbing, often develop a characteristic “shepherd’s crook” shape, and may die back. Infested needles are yellowed near the twig tips and eventually turn brown and die. All pines are susceptible, especially two- and three-needle species.
Biology and life history
The insect overwinters as larvae in the mined buds, covered with resin-coated webs. The adult moth lays eggs on new shoots near leaf bases in the late spring. The larvae hatch and bore into the needles, which turn brown by summer. By midsummer, they are mining in the buds and cease feeding by August. There is one generation per year.
Sampling and thresholds: Check for yellowed leaves at shoot tips in midsummer.
Management-cultural control
Prune and destroy infested tips in spring, before adults emerge. Be sure to prune far enough down the branch to remove the insects.
Management-chemical control (home)
1. azadirachtin (neem extract)