ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
Spiny witch-hazel gall aphids, Hamamelistes spinosus, cause bumpy ridges on the leaves of birch in the spring. The overwintering eggs are laid on witch-hazel in June and July. These eggs hatch the following spring and the new aphid nymphs crawl to the flower buds to feed. If the plant does not have flower buds, these aphids die! Feeding on the flower buds induces the plant to form a spiny gall. A second generation of winged aphids develops inside the galls, but then leaves and moves to birch. These winged aphids give birth to a scale-like generation that settles and hibernates on birch until the following spring. As the buds break, the scale-like aphids feed on the leaves and induce the birch to form corrugated galls. Winged aphids that migrate back to witch-hazel or wingless aphids called accessory females develop inside these galls. The winged aphids, which migrate back to witch-hazel, give birth to a generation of wingless males and females. These wingless aphids mate, and the females lay eggs for overwintering. The special accessory females produce additional generations of winged aphids which migrate to witch-hazel to give birth to males and females that lay eggs for overwintering. Thus, this aphid requires two full years to complete its cycle of life stages (confused yet?).
Pesticides should be applied at bud break in early spring to
prevent gall formation. This must be done every year unless the
witch-hazels can be found and eliminated. The alternation of hosts
is well known for other aphids (woolly apple aphid on apple and
elm, woolly alder aphid on maple and alder, and green peach aphid
on peach and many other hosts), but the spiny witch-hazel gall
aphid seems to have the most complicated life cycle. Ornamentals and Turf Insect Note No. 38 provides information on aphid
management.
The most common spider mite pest of conifers in North Carolina is
the spruce spider mite, one of the cool weather mites. Spruce
spider mites do most of their damage in spring and fall. Also,
spruce spider mites tend to feed on the older growth. However,
these mites usually do not cause dieback. Spruce spider mites are
relatively inactive in very cold weather and tend to die out in hot
weather. Because the spruce spider mite tends to feed on older
growth, thorough coverage is necessary to place the pesticide
inside the plant where the mites are feeding. This mite is not
particularly resistant to miticides. Kelthane is the old standby
for spider mite control. If Kelthane is unavailable, then one of
the horticultural oils or Cygon will do the job. The horticultural
oils are effective for spider mites and they also control armored
scale insects. Cygon is also effective and has the advantage of
being systemic. Some additional information on cool weather mites
is found in Ornamentals and Turf Insect Note No. 77.
The juniper scale is a fairly damaging pest. Infested conifers
often have
dead or stunted twigs and uneven growth. The juniper scale insect
is a very small (up to 1 mm) armored scale insect. The armor of
the females is circular to oval and is white and parchment-like.
In the center is a light-yellow cast skin of the earlier female
nymph stages. The armor of the male scale is oblong, white and
about 1 mm long. At one end is the pale yellow cast skin of the
crawler stage. Adult males are tiny insects resembling gnats with
four eyes and a tiny waxy tail filament. Little is known of the
biology of juniper scale insects. If they behave like other
armored scales, these scales hatch from eggs laid by the mother
scale under her armor. The tiny crawlers emerge to crawl about
seeking a suitable place to feed. Female scales molt twice before
maturing; male scales molt three times. Males emerge from the male
armor and seek females with which to mate. The males soon die.
Females soon lay eggs for another generation. After laying eggs,
the females die. The armor of both males and females clings to the
infested shrubs long after the scales inside die (females) or leave
(males). They are found on the needles and bark of Cedrus,
junipers, cypresses, spruce and Leyland cypress. Because they are
so small, juniper scales are easily overlooked. The juniper scale
is a debilitating pest of junipers and is considered an economic
pest. Insecticide applications are often required in commercial
nurseries for control. Horticultural oils or dimethoate (Cygon)
should give adequate control of the juniper scale. Available in
the county extension centers are copies of insect notes on
horticultural oils (Ornamentals and Turf Insect Note No. 45) and the Juniper Pest Control Calendar
(Ornamentals and Turf Insect Note No. 57).
Web page last updated on May 19, 1997 by Stephen J. Toth, Jr..
