ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable to North Carolina
and may not apply in other areas.
The wool sower gall is a distinct and unusual plant growth induced
by the secretions of the grubs of a tiny gall wasp, Callirhytis
seminator. If you have the chance to collect a fresh wool sower
gall, hold it in a plastic bag out of the sun (so it will not get
too hot). Within one to three weeks, the tiny gall wasps will
emerge. These wasps are harmless to people. The wool sower gall
is specific to white oak and only occurs in the spring. Pulling
the gall apart exposes small seed-like structures. The gall wasp
grubs develop inside these structures. (This gall is also called
the oak seed gall.) Fortunately, wool sower galls are hardly ever
abundant enough to cause harm to white oaks. If the galls are
actually damaging the trees, the best time to control them is
mid-winter when the wasps are laying their eggs or spring just as
the buds are breaking. The eggs hatch just as the new growth
emerges in spring. Orthene or some other contact insecticide
should give adequate suppression of these insects. However, by the
time the galls are noticed, it is too late to effectively control
the gall wasps. Gall wasps invariably have alternation of
generations in which one generation develops in one kind of gall
(leaf gall) and their offspring develop in another kind of gall
(stem gall). Wasps of each alternate generation are slightly
different is size and the galls of each generation are enormously
different from the parents. The wool sower gall is probably the
"leaf" gall of this species because of its transient nature. I do
not have a clue to what the stem gall looks like. Ornamentals and Turf Insect Note No. 5 gives additional information on galls. A copy should be in each county extension center in North Carolina.
The scolytid bark beetle, Xylosandrus crassiusculus, was introduced
from southeast Asia. It is sometimes called the Asian ambrosia
beetle. It was first found near Charleston, South Carolina in 1974
in peach trees. It also attacks cherry, Chinese elm, fig, golden
rain tree, magnolia, pecan, persimmon, plum, shumard oak, sweetgum,
and even sweetpotato. Female beetles bore into stems and young
trees. Visible symptoms include wilted foliage and strings of
boring dust that may protrude from the bark as tiny sticks or
tooth picks. These strands may reach 1.5 inches if wind and rain
do not break them off. The beetles are present most of the year,
but records at the North Carolina State University Plant Disease
and Insect Clinic indicate Asian ambrosia beetles are most active
in March. Eggs, larvae and pupae are found together. There are no
individual egg niches, larval tunnels or pupal chambers. High
humidity is required for successful reproduction. Adults and
larvae feed on a mold-type of fungus known as ambrosia the
beetles introduce as they tunnel into the sapwood and sometimes
heartwood of trees and logs. The fungus grows on the walls of the
tunnel. With this species, the beetles bore galleries straight
into the wood from 1 to 3 cm or more. The tunnels then branch one
to six times in the same plane following an annual ring. In small
trunks and branches, the galleries go straight in or spiral upward
from the point of attack around the stem or limb, branching upward
or downward from the spiral gallery. The Asian ambrosia beetle
seems to attack trees and shrubs more aggressively than native
ambrosia beetles that attack mostly dead, dying or heavily stressed
plants. Because most of the boring occurs in the sapwood or
heartwood rather than the cambium, it is usually possible to save
plants infested with Asian ambrosia beetles. I recommend that any
dead wood be pruned and the remaining stems be treated as soon as
convenient with lindane, Dursban or Thiodan, then treated again in
six weeks. There is little biological information on this pest.
It is difficult to predict how long the threat of the beetles will
last. It may be necessary to treat again in twelve weeks to
completely protect infested plants. There is some additional
information in Fruit Insect Note No. P-3. A copy of this note
should be in each county extension center in North Carolina.
Phylloxera are aphid-like insects that feed on the developing leaves of pecan or hickory and cause galls to form. The galls are green at first, but gradually turn brown and crack open. The phylloxera escape and lay eggs that develop into males and females. These insects mate and the females of some species crawl to protected places on the bark of the host tree and die. With these insects, a single egg inside the body of the female survives the rest of the summer, fall, and winter. Other species lay eggs on the leaves and twigs. These eggs hatch the following spring and the tiny, new phylloxera feed on the developing buds and form a new generation of galls. As the galls dry out, the leaves often fall prematurely. Heavily infested trees may suffer die back due to the disruption caused by the galls. There is no pesticide currently labeled for phylloxera galls on hickory. Infested trees are often too large for homeowners to treat practically.
Web page last updated on 27 May 1996 by Stephen J. Toth, Jr..
