Ask the Hort Agent: Tree Scale

  • Posted: Wednesday, January 22, 2014 11:38 a.m.
    UPDATED: Wednesday, January 22, 2014 11:42 a.m.

Question: What is the best way to kill scale on my trees?

Answer: Scale is a group of insects that fall into two general categories – armored scale and soft scale. There are several species of scale in each category. These critters hatch from an egg, crawl around, then mature and feed on your plant.  They are known for their defenses in the adult stage.

Armored scale are not only bullet proof as adults, they are often difficult to spot. Their shell-like covering helps them blend into the color and shape of the bark.  Most people can look right at them and never see em.  Soft scale are typically easier to see, but still difficult to kill as adults. Soft scale are often white with a waxy or cottony covering.

Soft scale species are susceptible to systemic insecticides like imidacloprid products (ex. Bayer Tree & Shrub Insect Control).  Armored scale are tougher nuts to crack. Both types of scale need air to survive.  Whether they are in the egg or overwintering adult stage, they need to breathe. Horticultural oil will smother them.  These oils can be used on deciduous and most evergreen plants. Most people think about fruit trees, but roses, junipers, deciduous magnolias and other plants can all benefit from a sneaky “off season” attack.

The best time to apply a dormant oil is when the buds are swelling on the plant, just about ready to break open. Insect eggs, like plants, are dormant during the winter. The closer the eggs are to hatching, the easier they are to kill. Many insect eggs may also be under some of the plant tissues surrounding the buds. When the buds begin to swell, the tissues expand and allow the oil to penetrate further into the plant. If you have trouble looking at a plant and determining whether the buds are swelling, then shoot for a late February or March application.

Spray the upper branches, twigs and trunks. Try not to spray the lower trunks with dormant spray because many beneficial insects lay their eggs in the lower parts of the tree. Spray to the point of dripping.      

While dormant oil applications also control aphids, spider mites, peach twig borers and more, they will not hurt birds and other non-target animals (or people). Horticultural oils are one of the safest products on the market and often used by organic growers. For more info about horticultural oil, visit http://www.ext.colostate.edu/pubs/insect/05569.html For more info about armored scale, soft scale and other insects, visit http://www.ces.ncsu.edu/depts/ent/notes/O&T/index.html  If you do not have internet access then call the Extension Office at (910) 893-7530 or email me at gpierce@harnett.org

When scale insects emerge from their eggs, they have legs and are called “crawlers.” They use this stage to move around (sometimes greener pastures are in order). They change their skin in order to grow up to an adult. For many species, the females lose their legs when they change their skin. Therefore, they stay in that spot for the rest of their lives. However, the males retain their legs and use them to seek females. I’m sure it’s easier to get a girlfriend if she can’t walk away.        
 
 
Gary L. Pierce, Horticulture Extension Agent - Harnett County

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