Scale Bugs

The scale bug is small, oval, and flat with a covering in varying shades. Scale-damaged plants look withered and sickly. Leaves turn yellow and may drop from the plant. They may also have sticky sap or a black fungus, depending on the type of scale bug.

These insects have a relationship with ants, which feed on the honeydew and protect them from predators. There are about 1,000 described species in North America.  Depending on the species of scale, insects may be found on plant stems, twigs, trunks, foliage, or fruit. Most scale insects are very small and inconspicuous hiding on the underside of leaves.

Scale insects are a common garden and indoor plant pests. Like other plant pests, they feed on the sap and nutrients running through the plant. This can cause aesthetic damages, usually in the form of discoloration. It is unlikely that scale bugs will do immense damage, however, depending on the amount of scale on a plant and what other pests feed on the honeydew created, the plant may not recover.

Scale insects feed mostly on trees, shrubs, and perennial plants. Some species prefer fruit-bearing trees like orange, olive, or lemon, while others attack a wide variety of flowering plants or even fruit and vegetable plants such as cabbage or beans. Unlike some other plant pests that mostly feed on leaves, scale insects may be found on leaves, bark, and other plant parts such as fruit.

Scale insects feed by inserting small, straw-like mouthparts into plants to suck out nutrients. Because scales feed on dark parts of the plant like the bark, it is easy for certain species and types of scale insects to blend in.

According to NJ.gov there are 30 different types of scale bugs in this state.  Their ‘season is from mid-May through September. These bugs attack trees from Azaleas to Hemlocks to Tulip trees.

Soft scale – These insects are relatively large sap-sucking insects, measuring a tenth to a quarter of an inch long (two to six millimeters), with a distinct protective covering attached to their bodies. The most distinguishing feature in determining soft scale versus armored scale infestations is the production of large amounts of a clear, sticky liquid called honeydew. Only the soft scale bugs produce this liquid, which drips down leaves. This sets up a dangerous cycle because the sweet liquid attracts both ants, as well as flies, bees, wasps; and a non-pathogenic fungus called sooty mold.

• Plants leaves that are droopy, yellowing, or have developed sticky spots and black mold on leaves can be really alarming to find in your landscape or garden.
• These are plants that look to be on the brink of immediate death. It may not be a terminal plant disease, but soft scale insects to blame.
• Some mimic their surroundings, others produce a waxy coating that can make them resemble fluffy insect casings.
• They come in a range of colors and sizes, but they all result in the same kinds of problems.
• Soft scale feed directly from the vascular systems of host plants, which can quickly result in a plant that appears to be doing poorly. Often, ant infestations are among the first signs of soft scale.

Ants use the soft scale insects as a means of farming honeydew, just as they do with aphids. Ants will tend them lovingly and then harvest the fruits of their labor for the ant colony. As soft scale are unable to move, their ant farmers will move them to more promising plants or to un-infested parts of the existing host, creating a bigger problem for the plant owner.

Destroying soft scale is a relatively easy process, except for those ants. If you are seeing ants in the same plant as the scale bugs, you will have to get the ants under control while you treat the invaders. Otherwise, the ants will rush in to save the soft scale insects and move as many as possible to a new, safe location. Baiting and applying a sticky barrier to affected plants will rid you of the ants, making it easier to control the scale. Horticultural oil sprays are recommended to get the scale themselves under control. The predators of scale insects need to be preserved as they will keep more scale from invading.  Make sure to test foliage before spraying your entire plant with any sort of oil. Most soft scales only have one generation per year.

Armored scale – When your plants suddenly develop a lot of unusual bumps, lumps, or things that look almost like they might be new growths in the wrong spots, armored scale is probably responsible. These scale insects are tiny, about the size of aphids. They have an oval, slightly elongated shape. They get their common name from the waxy, protective scale covering that covers their bodies while they feed. These scales are not actually a part of the insect but instead are external, protective coverings.

• Scale insects hide under elaborate coverings meant to protect them from predators and the elements, as well as acting as cover for their eggs.
• These covers are waxy, hard, and rounded in shape, and detached from their bodies.
• The females spend the bulk of their lives under these covers, eventually losing any obvious appendages and permanently affixing themselves to their host plant.
• Armored scale rupture and destroy the cells they are feeding on directly. As a result, no honeydew is created.
• Infected plants may suddenly appear weak or yellow dramatically when insect numbers climb.

These insects are vulnerable, except for the ‘armored’ cover to preventive measures. Horticultural oil is the best way to destroy armored scale while keeping the predators that will readily feed on scale young during the mobile crawler stage. Timing the application with the appearance of crawlers from their mothers’ covers can eliminate an entire generation all at once. Armored scales will often blend in with the bark of their host plants, meaning they might not be noticed until the damage becomes more apparent.

Some of the scale bugs found in New Jersey:

Gloomy scale – This insect has a gray shell that blends in well with bark. The small insects feed on the plant’s cells,  which results in slowed growth, branch dieback, and a decline of the infested plant.

• Gloomy scale occurs on soft maples like silver and red maple. It can also infect grapes, native hollies, sweetgum, boxed elders, and mulberry.
• This scale attaches to the bark of the tree’s trunk and branches.
• These insects feed on the plant sap which can cause a tree to decline. While it does not kill trees quickly, over time it causes significant damage.

Obscure Scale – The coloring is dirty gray on the top side, with a black cap that is slightly off-center. The underside of the waxy covering is black except for a white, silk-like coating in the center. Infested branches appear to be sprinkled with wood ashes or small pieces of glitter.

• The armored obscure scale is a major pest of oak and can attack others, such as beech, dogwood, hickory, maple, and willow.
• Interestingly, this insect is not a pest of these trees when they are growing in the forest.
• This pest overwinters as nymphs on host twigs and branches. Only one generation is produced each year.

The Pine Needle Scale – This is considered a pest of pines in landscapes, nurseries, and Christmas tree plantations.

• Primary trees infected include several pines, Douglas-fir, most spruces, and cedars.
• It is a native pest.
• Crimson red eggs are seen in early spring beneath the female’s white waxy cover. Adult males are small-winged insects that resemble tiny parasitic wasps.

White Prunicola Scale – This scale is native to Asia and is an armored scale. It feeds on the fluids/saps in trees and shrubs.

• Left untreated this insect infestation can harm or even kill your tree.
• It infects members of the Prunus species and various other ornamental plants.
• This is the most significant pest of cherry and peach trees.

The tree professionals at Precision Tree and Landscaping can help assess the possible damage and control procedures necessary to combat an infestation.  Early detection of an infested tree is critical for effective management.