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Soft scales can be more than just unsightly on trees and ornamentals.
These scales can cause premature leaf drop, reduction of vigor or twig death on
older plants and on younger plants cause severe stunting or even death. A
heavy scale infestation is usually an indicator of plant stress, often drought
stress.
Soft scales have piercing-sucking mouthparts that allow them to feed on plant
phloem. The plant phloem is not nutrient rich, so large amounts are
ingested. This results in considerable amounts of honeydew to be excreted
from the scales, which may cause sooty mold to develop on leaves.
Female scales are usually wingless and legless. Some species do not
have males, so they reproduce asexually. However if males are present,
they have definite body regions, wings and antennae. The males are mobile,
so are usually not seen. The unmated females usually overwinter on twigs
under their protective waxy caps. The males, if present, will overwinter
in pupal cases.
In the spring, the males and females become functional adults. After mating,
the female will lay 200-1000 eggs under its waxy protective cap. The eggs
will hatch and the crawlers will emerge from the waxy cap to feed on new leaves
and twigs. Then the crawlers will move to larger branches to settle and
begin forming their own waxy protective cap.
Some Control Tactics
Non-Chemical Control Tactics
1) Keep plant properly watered and fertilized to help minimize scale
populations.
2) Plant trees in appropriate sites and at proper soil depths.
3) Prune infested twigs and leaves to protect new growth from infestations,
then discard plant material.
4) Natural enemies such as predators and parasitoid wasps will gradually
reduce scale populations.
Some Chemical Control Tactics
There are many chemical control options for scales, but chemicals lower in
toxicity should be applied first to avoid killing natural enemies. One
option is horticulture oil or insecticidal soap that should be applied at the
crawler stage. Both of these options are contact insecticides.
Another approach is to apply a systemic insecticide, such as those containing
imidacloprid. Generally systemic insecticides should be applied early, so
plants have enough time to take up the chemical before scales begin feeding.
Eventhough the scales might not be alive, the caps will remain attached to
the plant. Therefore scrubbing the plant with a soft brush or mesh sponge
will remove the dead caps and increase the overall appearance of the plant.
Photo of a brown soft scale, Coccus hesperidum
Linnaeus (Homoptera: Coccidae).
Photo by Dr. Bart Drees, Professor and Extension Entomologist,
Texas AgriLife Extension Service, Texas A&M University.
Moving plants indoors during the winter allows for excellent breeding
conditions for many insects. One of these flying insects a leafminer
agromyzid fly in the genus Liriomyza. Liriomyza leafminers can be found on
numerous outdoor plants, including chrysanthemums, asters, zinnias, marigolds,
daisies, eggplant, carrot, potato, garden peas, lettuce, tomato, cucumber, and
pepper plants.
Adult leafminers are 1/16 inches in length with grayish-black bodies and
yellow markings. The female flies insert their eggs into the leaves. The
eggs hatch usually in 2 days into 1/16 inch larvae. These whitish-yellow
larvae cause plant damage, by tunneling through the leaf tissue. As the larvae
mature, the tunnel or mine gets larger in size. After 7 or 8 days, the
last larval stage emerges from the leaf to pupate in the soil. The adult
fly will emerge usually in 7 to 11 days. The lifecycle from egg to adult
may last all year, if the leafminer is in a controlled environment.
The white tunnel that appears on the leaf is both unappealing to the eye and
can cause leaf drop in some instances. Leaf mines reduce the value of the crop
and they can reduce the photosynthetic ability of the plant. If large
populations exist, they have the potential to retard growth of young plants and
lower fruit yield.
Some Control Options
Some Cultural Control Options:
1) Prune off and dispose of infested leaves and branches.
2) Properly irrigate and fertilize plants to ensure healthy plants.
3) Plant cultivars that are more tolerant to leafminer attack.
4) Cover the soil with plastic to prevent larvae from pupating.
Some Chemical Control Options:
Organics sprays such as horticultural oil, neem and spinosad can be used to
control leafminers.
Systemic insecticides such as acephate and imidacloprid can be used to
control leafminers.
Photo of leafminer adult, Liriomyza sp. Photo by:
Texas AgriLife Extension Entomology,
Department of Entomology,
Texas A&M University.
Shore flies are usually found in greenhouses, since they are attracted to
algae growing on potting soil and under greenhouse benches. However, they
can be found on house plants as well. Shore flies are frequently confused
with fungus gnats, since they are usually found together. However shore
flies have short antennae, a large head with red eyes, and smoky gray wings with
5 white spots on each wing. Also shore flies are stronger, faster fliers than
fungus gnats.
Female shore flies will lay eggs singly on the surface of algae. The
eggs will hatch in about 2 to 3 days. Shore fly larvae are ⅛ inches in
length, with a brownish-yellow, legless body. The larvae lack a distinct head
capsule, but their dark mouthparts and internal organs may be visible. The
larvae feed on algae growing on the surface of the potting mix. The larvae
mature in 3 to 6 days and then pupate. The pupae are also found close to
the soil surface. The adult fly will emerge 4 to 5 days later and it will
feed on the same material as the larvae. The adult fly usually stays close to
the breeding sites.
Even though the shore fly adult and larva do not feed on plants, they still
can present problems. Adults can be a problem, since they can transmit
plant pathogens, such as Pythium and other root disease organisms. Also
shore flies produce excrement that can land on foliage, leaving unsightly black
specks.
Some Control Options
Non-Chemical Control Options:
To reduce shore fly numbers avoid over watering and limit fertilizer run-off.
Algae should be cleaned from under and on benches, walls, and floors. All
doors and windows should remain closed or screened to prevent the invasion of
shore flies. Compost should be aerated often and relocated away from doors
and windows. Allow soil to dry before watering again. Remove standing water
and eliminate any plumbing or irrigation system leaks.
Some Chemical Control Options:
Some chemical control options include using the active ingredients bifenthrin,
permethrin to control adults and azadirachtin, cyromazine to control larvae.
Picture of adult shore fly. Photo on
http://mrec.ifas.ufl.edu/lso/fungusgnats.htm
Mention of commercial products is for educational purposes only and does
not represent endorsement by Texas AgriLife Extension Service or The Texas A&M University System. Insecticide label
registrations are subject to change, and changes may have occurred since this
publication was printed. The pesticide user is always responsible for applying
products in accordance with label directions. Always read and carefully follow
the instructions on the container label.
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