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Be On the Lookout for Soft Scales

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. 

brown soft scale
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.

Mining the Leaf

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. 

LeafMiner Adult
Photo of leafminer adult, Liriomyza sp.  Photo by:
Texas AgriLife Extension Entomology,
Department of Entomology,
Texas A&M University.

Presence of Shore flies

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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