Needles may turn brown and drop on spruce trees for several reasons. Before you
become alarmed or treat the tree with a pesticide, you need to find out why the needles are
dropping. Only then can you use appropriate treatment if the tree even needs one. Like all
evergreen plants, both needled and broadleaf, spruce trees eventually drop foliage. An individual
needle will naturally stay on a spruce branch for 2-3 years, and then turn brown before dropping.
It is possible to mistake natural needle fall for a pest problem. Natural needle fall occurs mainly
on the inside of the tree and the older sections of the branch. It does not occur on or near the
branch tips where the newest needles are located. Natural needle fall is seldom conspicuous on
spruce trees. Natural needle drop on pines, particularly on white pines in the fall, can be very
obvious and may cause you concern if you are not familiar with it.
Cytospora canker, a fungal disease, is the most common reason for unnatural needle drop
on Colorado blue spruce. It also occasionally occurs on Norway spruce, but rarely on white
spruce. Cytospora canker is a very common disease of older, mature Colorado spruce in the
Midwest. The first symptom is browning of needles at the tips of the branches, followed by
death of the lower branches. Over several years, it spreads upward to other branches. Dead
areas, called cankers form at the base of the branches, but do not discolor or become depressed.
Instead, resin flow is seen, causing conspicuous patches of white resin on the bark. Cut out all
cankered branches, avoid making unnecessary wounds, and keep the tree healthy and vigorous.
Stress leads to more severe canker development. If the tree becomes a visual liability, it is best
to remove it. Fungicides are not an effective control measure.
Rhizosphaera needlecast is another cause of needle drop. This disease also tends to start
on the lower branches and moves up the tree. It does not attack individual branches, but rather
several branches all at one time. The first symptom appears in late summer when needles are
speckled with yellow blotches. Later the needles turn brown or purplish brown on blue spruce.
The needles drop the following summer or autumn, about 12-15 months after infestation. Close
inspection with a hand lens reveals rows of distinct black specks on affected needles. These
black specks provide positive diagnosis for Rhizosphaera needlecast. This disease rarely kills
trees, but heavily infected trees may suffer severe needle loss. If the tree is severly defoliated 3
or 4 years in a row, some branches may die. It is best to let an expert diagnose this problem
before the tree is treated.
Spider mites can also cause needle drop on spruce trees. Mites are a potential problem on
all spruce trees. As spider mites feed on the needles with their sucking mouth parts, they cause
the needles to turn dull and eventually become yellowish green and drop. Close inspection with
a hand lens will reveal a fine webbing between the needles. Another way to check for mites is to
hold a piece of white paper beneath a branch and shake the branch vigorously. If mites are
present, you will see tiny, moving specks on the paper. Minor infestations can be treated by
showering the tree with a strong spray from the garden hose. If the infestation is heavy, chemical
treatment may be required. Check with your local nursery or garden center for currently
available sprays for spider mites.