ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable
to North Carolina and may not apply in other areas.
Photo Gallery of Insects and Mites on Ornamental Plants
This is the second time the western flower thrips has been featured
in the North Carolina Pest News this spring, but because several
commercial greenhouses visited this week were heavily infested with
western flower thrips and impatiens necrotic spot virus, it seems
appropriate to remind county extension agents that growers with
medium to small operations may not recognize the symptoms nor
realize the magnitude of the problem of western flower thrips
spreading impatiens necrotic spot virus in greenhouses. The
western flower thrips has acquired resistance to a variety of
pesticides and has become a double threat to ornamental plants
because it can also transmit impatiens necrotic spot virus and
tomato spotted wilt virus. This thrips readily overwinters in
greenhouses. One threat to greenhouse plants is that western
flower thrips in South Carolina and Georgia may pick up tomato
spotted wilt virus there and then blow into North Carolina and be
sucked into greenhouses where they can then spread the virus among
susceptible crops. Another threat is that western flower thrips
may blow into greenhouses and become established (because of its
great pesticide resistance); later a plant with impatiens necrotic
spot virus may be brought in and the virus acquired by immature
western flower thrips and spread through the rest of the range by
the new, infected adults. It is extremely difficult to rid a
greenhouse of both thrips and viruses. Avid is the most effective
pesticide for western flower thrips management (it is moderately
effective). Several applications two or three times a week are
necessary for good suppression. Other pesticides labeled for
thrips management in the greenhouse include chlorpyrifos
(Duraguard, a new microencapsulated formulation from Whitmire that
is less phytotoxic than the older chlorpyrifos formulations).
Carzol (a 24(c) registration in North Carolina) is also effective,
but has a very high oral toxicity to humans. Both chlorpyrifos and
Carzol are somewhat effective for western flower thrips management.
The advantage of using Avid is that it would also control broad
mites. The agricultural formulation of Dibrom is labeled for
thrips suppression on greenhouse ornamentals. Dibrom is phytotoxic
as a spray and as a thermal fog, but Dibrom can be applied as a
smoke from a hot plate. The hot plate can be set up on a timer so
the fumigation takes place after working hours. Set the hot plate
to 160 degrees F. The greenhouse will have to be ventilated the
next morning before it can be reentered. In addition, Mesurol WP
from Gowan Company is labeled for aphids, mites, slugs and snails
in the greenhouse and supposedly controls thrips well although it
has not been tested in our experimental greenhouses. Ornamentals
and Turf Insect Note No. 72 has some additional information on the
biology and control of western flower thrips.
The maple spider mite, Oligonychus aceris, is an irregular pest of
maple (not that the mite needs more fiber in its diet, the mite
occurs at infrequent intervals). This mite will not feed on the
twigs or stems of maple, only the green leaves. It must overwinter
as a non-feeding hibernating stage or as eggs on the fallen leaves
and on the twigs. Relatively humid weather encourages entomopathic
fungi (Neozygites) to destroy these mites. Sample for the mites by
striking the leaves on white paper to see if there are any mites
left. If you have some Kelthane, this would be a good situation to
use it up. Because mites in the genus Oligonychus are not
resistant to miticides, control should not be a problem as long as
coverage is thorough.
The hemlock woolly adelgid, Adelges tsugae, is called the hemlock
chermid, the hemlock chermes, the hemlock woolly aphid, and the
hemlock woolly adelgid. This insect is now in Stokes, Surry and
Rockingham counties. This is an EXTREMELY damaging pest of
hemlock. The hemlock woolly adelgid is thought to have originated
in the Orient. It has been known for some time to occur in the
Pacific Northwest and the Northeast and has gradually spread
southward into Virginia and now North Carolina. Infested branches
become covered with 3 mm round, fluffy white insects that resemble
woolly aphids or mealybugs. The hemlock woolly adelgid is
difficult to control because the fluffy white secretion protects
the eggs from pesticides. Insecticidal soaps and horticultural
oils seem to give adequate control perhaps because both of these
pesticides are also useful as surfactants and evidently penetrate
through the fluffy covering of the adelgids. Additionally,
diazinon, Mavrik and Dursban are labeled for the hemlock chermes.
Web page last updated on June 9, 1997 by Stephen J. Toth, Jr..
