Landscape Update

 COMMON PESTS IN THE TRI-CITY AREA-  The following paragraphs discuss several of the insects pests commonly identified in the mid-Michigan landscape.


EMERALD ASH BORERS are currently present in Saginaw County, and the county is now a quarantined county. Midland county has had several outbreak areas, but is not yet a quarantined county (3/12/08).  Bay City and Mt. Pleasant have experienced outbreaks also, with significant tree damage and loss.  If homeowners want to save ash trees, we have proven methods to prevent serious borer infestation.  TRUNK INJECTION of larger trees and GROUND INJECTION or DRENCH of smaller trees have been shown to be effective if applied properly and in adequate dosage. Properly timed insecticide sprays can also be used.  We have a detailed discussion of this pest and effective control measures on the Emerald Ash Borer page.

BRONZE BIRCH BORERS (close relatives of the emerald ash borer) kill or disfigure many landscape birches in this area.  These borers can also be prevented by TRUNK INJECTIONS or ROOT INJECTIONS with an insecticide which kills the borers before they can do damage.  The injections also control BIRCH LEAF MINERS that cause brown spots on the leaves of many birches (a cosmetic problem).  Sprays can also be used to control the adult phase of these borers, but it is difficult to get excellent control with this method.

COTTONY MAPLE SCALE  (CMS) and LECANIUM SCALES are very common in this area, possibly due to the wide-scale spraying for mosquitoes, which kills some of the natural enemies of this pest.  These "soft" scales are a nuisance, causing much honey-dew falling onto surfaces below and sooty mold growing in the honey-dew.  We have developed very effective ways of dealing with these scales.  See page on Scale Treatment.

Scale Treatment
Emerald Ash Borer


APHIDS.  Aphids are common insects in the landscape, but rarely need any treatment.  They usually do not cause any significant harm or stress to trees.  Spray companies often will tell homeowners that they are spraying for "aphids and mites", and in fact may be using chemicals which kill those insects, but it is usually unnecessary and the spray may be killing beneficial insects that would usually keep populations of aphids and mites under control.  Aphids do excrete honeydew and can be a nuisance in that way, however, the most significant honeydew drippings are usually due to scale insects.

GYPSY MOTHS AND CANKERWORMS can cause defoliation damage to oaks, maples, ash, and some other deciduous trees. PINE SAWFLY caterpillars can cause defoliation damage to Austrian, Red, Scotch and Mugho pines. When significant populations of these pests are present, they can be controlled with biologic or chemical pesticide sprays.

ERYPHYOID MITES can cause gall formation such as MAPLE BLADDER GALLS and ASH FLOWER GALLS, which are primarily cosmetic problems. These mites can be difficult to control with sprays, but newer injectables may offer some promise in controlling them. 

SPIDER MITES can also cause discoloration of foliage and defoliation when populations are large. Selective miticides are used to control the harmful mites while preserving natural predator mites and insects.  These mites attack burning bushes, Alberta spruces, boxwoods, serviceberry, and some other landscape trees and shrubs almost every year, but a mid-July spray can usually prevent the problem.

BASSWOOD LEAF MINER BEETLES have become quite common in our area and cause damage to leaves of native basswoods and some ornamental linden trees.  They may have several generations per season, with the larval stage mining the leaves and the adult beetle phase skeletonizing leaves.  A well timed spray in May, possibly followed by a second in June can prevent most of the damage.  Injectables may offer long term control without the need for spraying.

TWIG GALLS ON OAKS.  Each year we get many calls about gall formations on oak trees. There are literally dozens of different types of galls which form on leaves, petioles (leaf stems), and twigs of oak trees. Most are caused by some type of insect. Perhaps the most persistent and most common cause for customer calls are the twig galls. Twig galls are hardened woody swellings on the twigs of oak trees, seen best when the leaves are not present. They vary in size, with the average being about the size of a golf ball.
TYPES. The two common types seen in Michigan are Gouty Oak Galls and Horned Oak Galls. Both are caused by a type of wasp. The wasp deposits its eggs in the twig and as the larva develops, a swelling of the woody twig tissue develops. Each of these “galls” contains several developing larvae. In the spring, the adult wasp emerges and feeds on the leaves for a time, then mates and lays eggs in twigs and the cycle begins again. The cycle may be two or three years in duration.
NATURAL HISTORY. The old galls never shrink away, but remain present for as long as that branch or twig remains on the tree. Sometimes the twig is killed beyond the gall, but that is uncommon. The galls seldom cause large branch dieback, even when present in large numbers. They are primarily a cosmetic problem which is much less obvious during the summer when leaves are present.
MANAGEMENT.   Sprays could be applied during the adult phase, but would involve spraying large heavily foliated trees with insecticides several times without good evidence that it does much to improve the problem. Trunk injection of insecticides may prevent new galls from forming, but will not rid the tree of the old ones.  We recommend deep-root fertilization of trees once every two to three years to help maintain vigor and healthy foliage. The galls are far less noticeable in the summer months, especially if the trees have healthy, thick foliage. If branches die, they should be pruned during the months of September through March, avoiding the warm months when the beetle vector of oak wilt is active.

TRUNK INJECTION.  Trunk injection may give control of this pest.  If a tree has soft scale infestation (lecanium scale), injection will control both the scale and the galls.  It is difficult to document and quantify the results on the galls, but it will be easy to document success with the scales.


 TriCity Tree Doctor  Call us at 989-454-0227

United Tree Service  Call us at 810-266-4363