How They Become a Problem Contniued
If scales are not introduced by way of transportation of the pests with the plants, then they will come from the surrounding habitat — albeit slowly. Since only the adult males have wings it doesn’t seem likely or logical that they begin the infestation process. My thought is the immature or crawler stages, which are mobile, slowly spread the population to other hosts. In addition to actually crawling, I suspect some hitch rides on water runoff, wind, people and animals and the like. Remember to scout new plant material thoroughly before bringing it into your greenhouse or interiorscape account. At least that may prevent the one factor which is most likely to spread these pests from ever occurring. [Intro]
A Serious Pest
Scales can cause considerable economical damage They, like aphids, have a proboscis, stylet or straw-like mouthpart which they insert into the phloem or inner cells of a plant. Upon insertion the scales draw the plant’s juices or sap. This feeding activity generally goes unnoticed until the plant or tree begins to weaken and die. At this point the subject may be beyond the self-reparation stage. It is therefore imperative the scout notice the pests and begin corrective actions before the plant shows outward signs.
The presence of the scales will make a plant unsalable. Soft scales will appear as bark-colored bumps on the twigs and leaves generally. With close scrutiny, any quasi-talented scout will notice them. Mealybugs are typically whitish in color and can, too, be very noticeable. In addition to the mealybugs themselves, one may notice their cottony egg-masses-which are produced by most mealybug species, though not all (long-tailed mealybugs, for instance, reproduce viviparously, giving birth to live young making egg-masses obsolete). Armored scales are generally very small and are the most difficult to detect. However, in most interiorscape and greenhouse situations, I’ve found the most common scale insects are soft-scales and mealybugs. Though armored scales do indeed make their mark in these types of plantings, they generally seem to be more of a problem on citrus and other trees and shrubs. [Intro]
Some Advice
One aesthetics problem, if a soft-scale or mealybug population becomes large enough, is the formation of black-sooty mold which grows on the sugary, ant-attracting excrement or honeydew of these pests. This excrement is known to attract sugar-feeding ants which may, in an effort to manage their food source, protect them from biocontrols, natural and introduced. This last condition, if the scale population grows large enough to support ants, can make non-chemical control even more challenging. Armored scales do not produce honeydew, so this isn’t a factor to be concerned with when dealing with them. This little bit of information, though, can help you with the identification process. [Intro]
For The Scout
So, as I wrote before, you need to scout well before the plants are included in your collection. Look for the following: Three to six millimeter bumps on a log with shiny, sticky honeydew probably indicates soft-scales; One to three millimeter specks with no honeydew may indicate the presence of armored scales (and both soft and armored scales have hard outer coverings so don’t be confused by the names); Three to seven millimeter white insects with shiny, sticky honeydew and cottony egg-masses (in most cases) may mean you have mealybugs. Unless they’re root mealybugs, which look like their above ground counterparts but are extremely difficult to control and can only be found within the root ball and crown, they should be readily apparent and easily identifiable.
Scales can be extremely difficult pests to deal with — especially if you’re in a hurry as control, chemically or biologically, can take a while. By far, based on my experiences with growers, mealybugs are the easiest to detect, the most common to have, and the simplest to control biologically. Remember: scout well and detect them as early as possible for the best possible results. [Intro]
Some Solutions
There are several commercially available scale controls available. The parasitoids are fairly selective so you must have a proper identification. However, if you’ve identified them well, have chosen the correct biocontrol agent and have introduced them in the right environment, you can have very long-term control and great success. The predators tend to be opportunistic and provide faster results to a wider selection of pests. However, they don’t stay in place as long thus shortening the control period. They will usually, except in the most ideal conditions, require multiple reapplications at maintenance intervals. Often, the best thing you can do is simply put the plant outside and let Mother Nature pick the predator or parasitoid for you.
Looking for controls? We discuss several on this site, good bugs such as Aphytis melinus, Cryptolaemus montrouzieri, Leptomastix dactylopii, Harmonia axyridis, Metaphycus helvolus, Rhyzobius lophathae, and Cybocephalus nipponicus. Most are commercially available. Other controls include soap and oil, and some biorational products. [Intro]
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