Woolly Adelgid Is Special Hemlock Problem In East
An aphid-like insect, the Hemlock woolly adelgid (Adelges tsugae) is by far the most serious pest of Canadian and Carolina Hemlocks, killing whole forests of them from New England to North Carolina. Adelgids are easily identified by deposits of white, cotton-like masses on the underside of Hemlock needles. Adelgids feed on the sap at the base of Hemlock needles primarily on new twig growth. They usually start on the lower branches. Needles turn gray then yellow and then drop off. Branches die back, and growth is slowed. Typically, untreated trees die after 4 to 8 years, depending on their size, stress level, and location. Trees of all sizes and ages are attacked.
Adelgids reach maturity between late winter and early spring at the base of individual needles, covering themselves with white, cottony wax for protection. They lay brownish orange eggs under the cottony wax that hatch from February through June. Wind, birds and animals spread the eggs from tree to tree throughout the spring. For more info about the Wooly Adelgid Click Here
The newly hatched nymph stage is very vulnerable to control by sprays of neem soap or light horticultural oil ( for more info on these products Click Here. If trees are small you can do this yourself. Hire a professional arborist to spray larger trees. Spray in the spring and again in the fall. Read the label instructions. Do not spray if temperatures are over 90°F. Thorough coverage is important, so use a compression sprayer to achieve good control.
Tricks to avoid spreading the dreaded adelgid
Avoid placing bird feeders in Hemlocks, as birds pick up adelgid eggs and nymphs in their feathers and spread them to other trees.
Because the pests thrive on trees rich in nitrogen, do not fertilize infested Hemlocks. Research shows that twice as many adelgids survived on fertilized Hemlocks as on unfertilized trees, and the survivors laid twice as many eggs!
Avoid moving Hemlock cuttings or brush from infested trees to new garden areas. Put them in the trash.
There is hope on the way, since 1999, many government and private organizations have been raising and releasing Japanese ladybugs which consider woolly adelgids to be ice cream. Because a single Hemlock tree can be infested with 100,000 adelgids at one time, it will take a number of years for the lady bug to reproduce enough to truly get control of the pest. Maybe in five to ten years, easterners will be able to plant and enjoy the Hemlock again.
Other Occasional Situations
Dead or Dying Lower Branches
Cultural conditions - Sometimes the lower branches on Hemlocks turn brown and die. Assuming the trees have sufficient moisture and nutrition, and no obvious insect problems, this is probably due to environmental factors. Most commonly it is because the lower branches are denied sufficient light by nearby plants that have grown large and shade them. Prune adjacent trees and shrubs to permit light to reach the bottom of the Hemlock.
The Hemlocks may not be getting their share of nutrients and moisture because of competition from lawn grass or other nearby plantings. A generous mulched area under them will reduce the competition. Trees under stress from the chronic light, water, and nutrient deprivation are vulnerable to pest insects such as mites and scale that zero in on unhappy plants.
Branches and Needles Eaten
Deer - Unfortunately Hemlock needles and twigs are tasty to deer. As the pressure of development restricts their habitats more severely than ever, deer and other animals are forced to feed in residential landscapes. Here they often find plants that are tastier than the wild ones they normally forage on. For more info on deer Click Here
Mites - Two-spotted spider mites and spruce spider mites cause discoloration of Hemlock needles. These mites are barely visible, only about 1/50 inch long. Related to spiders, they have four pairs of legs, piercing-sucking mouth-parts, and very compact bodies. They may be yellow, green, red or brown. Inspect Hemlock foliage for stippling or discoloring of the needles, possibly accompanied by telltale fine webbing. For solutions for mites Click Here
Small Bumps on Needles
Scale - Hemlock scale and Hemlock fiorinia scale attack Hemlocks. Scale insects feed beneath small bumps or blister-like protective shells that they form as they crawl on stems and leaves. These shells may be white, yellow, or brown to black, and are about 1/10 to 2/5 inch in diameter. The first sign of a scale attack is often discoloration of needles, followed by needle drop and loss of tree vigor. Some scale species also excrete honeydew, which coats foliage and encourages ants and growth of sooty mold. For solutions for scale Click Here
Spiny Bags Dangling from Branches
Bagworms - Bagworms sometimes infest narrow-leaved evergreens such as Hemlocks. These caterpillars fashion elongated protective sacs around themselves as they feed. The sacs are 2 to 3 inches long and appear to be shingled with tiny sticks--Hemlock needles. The sacs grow as the caterpillars within grow from feeding on the Hemlock foliage. Adult female bagworm moths lay their eggs in these bags; the eggs over winter and hatch in May or June. For solutions for bagworm Click Here