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Treating Tree Diseases and Pests with Microinjection

By Terry A. Tattar, Ph.D.,
Professor, Shade Tree Laboratory,
Department of Microbiology,
University of Massachusetts

For this microinjection technology to be used effectively and not cause harm to the tree, the clinical applicator must receive training in its correct use. One-day short courses on the proper application of microinjection therapy are presented in most areas of the United States during the winter conference season. Information is available from Artistic Arborist, Inc. or by contacting

Why Is Microinjection Important?

Lawn and landscape professionals are increasingly being asked by homeowners, and condominium and apartment managers to control health problems of their trees. Tree insect and disease problems also occur suddenly on clients properties and frequently create crises that demand immediate attention.

A tree suffering from leaf scorch, which is caused by bacteria that can stay alive in the roots during the winter.

Application of sprays to shade trees in urban areas, however, requires specialized, expensive equipment and has a negative public image. For example, if a hospital, nursing home, school, pond, stream or river is nearby or your clients and/or their neighbors have pets, wildlife concerns or chemical sensitivities, spray application may not be a tree health care option. Microinjection, however, is a technique that allows the introduction of materials, such as antibiotics, fungicides, insecticides and mineral nutrients, directly into a tree without any contact with the environment. Microinjection has become an increasingly popular clinical alternative to spray applications in the control of health problems of urban trees. It can also offer an opportunity for lawn and landscape professionals to provide an important new service to their clients.

What is Microinjection and How Does it Work?

Microinjection is a type of trunk injection where small amounts (approximately 0.1 ounce) of therapeutic chemicals, contained in sealed capsules, are introduced into shallow trunk wounds around the base of a tree. The injected chemicals are then distributed systemically within the tree to the branches, leaves and even roots within a few hours after injection by sap movement.

Although the trunk injection has been known since the middle ages, it is a technology that is often misunderstood. Materials in liquids can be injected into the woody tissues, known as xylem, of trees because the pressure within the xylem is below that of atmospheric pressure on the outside of the tree. Under this condition of negative pressure, liquids introduced into healthy xylem through a fresh injection wound will be taken into the xylem and distributed within the tree in the sap stream.

The microinjection procedure: Very small holes are drilled in the root flares; the microinjection capsules are then seated with a mallet and pressurized.

There is no need for the use of high pressures to attempt to “force” liquids into the tree. High-pressure injection often damages tree tissues and does not place the injected materials into the outer xylem where most systemic transport occurs. Low pressures sufficient to empty the injection reservoir are most effective for transport and cause the least impact on the tree.

Trunk injection of several gallons of materials per tree, or macroinjection, has been used primarily to treat trees with vascular diseases, such as the Dutch elm disease. Unfortunately, most tree species do not have the xylem porosity of the American elm and cannot accept large volumes of liquids via trunk injection. In addition, macroinjection systems involve complex tubing and reservoir systems that are very labor intensive and are not practical for rapid treatment of numerous trees.

The cambium is the only part of the tree trunk that grows. The cambium is a single layer of growing cells just under the bark. It produces wood (xylem) cells to the inside, and bark (phloem) cells to the outside. Bark can be very thin or very thick. The bark of a birch tree may be only one-quarter inch thick, while the bark of a giant sequoia can be as thick as two feet.

A breakthrough in injection technology occurred in the 1960s when the systemic insecticide Bidrin, in microinjection capsules, was injected into trees and shown to control a variety of chewing and sucking insect pests.

It was then clear that large volumes of materials did not need to be injected into a tree to control a tree health problem. Research on Bidrin demonstrated that a small volume of a concentrated systemic chemical in a microinjection capsule could provide effective tree health care.

Anthracnose: The symptoms include large, irregular tan to brown lesions and along the margins of the leaves that drop very prematurely. It occurs after a cool wet spring. These are the early signs of anthracnose on a California sycamore.

Since that time the focus of microinjection research has been to develop systemic formulations of antibiotics, insecticides and fungicides that were effective in low volumes. Considerable research has gone into studies of the most effective injection techniques to maximize uptake and distribution and to minimize any effects of wounding of the tree. Recently, combinations of an insecticide and a fungicide in a single capsule have been developed to allow microinjection treatment of both insect and disease problems with a single injection.

Interveinal chlorosis in oak leaves is evident by the yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity or nutrient deficiencies (manganese, zinc or iron).

Today, microinjection is both an evolving, research-based technology and a clinical tool for the tree health care practitioner. Research on microinjection is continuing on the potential systemic uses for new tree health care chemicals that are being produced and registered each year.

Fall Applications of Microinjection Treatments

Fall is a time when many tree health problems can be effectively treated. As trees in temperate climates and subtropical climates go into dormancy many plant pathogens and insect pests continue to be active. In some cases, fall treatments lower pest and pathogen populations and give trees protection against health problems in the following spring. In addition, the root growth without shoot growth that occurs in the fall facilitates treatments of nutrient abnormalities at this time. The amount of sap movement is less in the fall and early winter compared to the spring and summer when large amounts of water are lost through the leaves during transpiration.

Specific Tree Health Problems for Fall Microinjection

The following four examples are common tree health problems that can be treated in the coming fall months by microinjection technology:

  1. Leaf scorch diseases of hardwood trees – Bacteria, which live in the xylem, cause leaf scorch diseases on a number of hardwood hosts including elm, mulberry, oak and sycamore. The pathogen over-winters in high populations in the roots. Symptom remission can be achieved by microinjection of oxytetracycline antibiotics in the fall. The antibiotic treatment, however, does not eradicate the bacteria, and treatments have to be repeated within every one to two years to keep the infected tree in remission.

  2. Adelgids create a white cottony deposit, mostly on the undersides of stems. The hemlock woolly adelgid can kill a hemock in a year, a significant problem in the northeast U.S. if not treated. Injecting imadacloprid can provide protection for the tree for a year after injection. Nature’s helper is this lady beetle (Pseudoscymnus tsugae), a natural predator of the hemlock woolly adelgid. Adelgids are decimating stands of the majestic and ecologically significant eastern hemlock.

  3. Adelgids on coniferous hosts – Adelgids are close cousins to aphids, but their health impact on coniferous hosts is often more severe. The hemlock woolly adelgid, an imported pest, can kill an infested hemlock in one year if the tree is not treated. This insect is most active in cool weather and can be effectively eradicated by microinjection of Imicide(R) (imadacloprid) insecticide. This insecticide has been shown to be extremely stable within plant tissues and often provides protection for one year after injection. Microinjection capsules are placed onto the hemlock trees in the early fall. This timing helps to eradicate the existing adelgids and prevent reinfestation during the next spring and summer seasons.

  4. The California Department of Pesticide Regulation has approved a phosphite product developed by AGRICHEM, an Australian company, for use as a spray or for injection to combat sudden oak disease (SOD) caused by the Phytophthora ramorum fungus. SOD is a coastal killer of oaks that has spread to at least 27 tree and shrub species, most of which host the disease. Some arborists believe acidic soils that leech calcium and phosphorus from the soil are the culprits, not the fungus, and have been injecting the oaks with phosphite fertilzer.

  5. Anthracnose diseases of hardwood trees. The fungi which cause anthracnose diseases in the spring and summer on many species of trees including, ash, dogwood, maple, oak and sycamore are also active during the warm periods in the fall. It has been long recommended that fall treatments for sycamore anthracnose will decrease bud mortality and minimize symptoms in the following spring. Fall microinjection of fungicides can provide protection for recently formed twigs and buds and may help to improve the overall appearance of the trees during the spring growing season.

  6. The necessary tools for microinjection include a drill, the chemical capsules and a mallet.

  7. Nutrient abnormalities on all trees – Mineral nutrient deficiencies cause health problems, such as chlorosis, on many species of trees. A soil or tissue test is often needed to confirm the exact nature and severity of the deficiency. Many of these mineral deficiencies, such as iron deficiency and manganese deficiency, can be corrected by microinjection during the fall season because the root system is actively growing at this time. Minerals are quite stable in the tree and are available to be transported during the next spring and summer growing seasons. In some urban locations, the soil surface is covered with asphalt, bricks, cement or a wood deck, and microinjection provides the only practical approach to the application of mineral treatments.


Fall microinjection of fungicides can protect recently formed twigs and buds from anthracnose disease.

Tree health care is an expanding area of need and opportunity for the lawn and landscape industry. Microinjection is a contained, delivery system that presents the applicator with an environmentally friendly alternative to spray applications.


Dr. Tattar has conducted extensive research on vascular transport and vascular diseases of trees and often presents seminars on microinjection technology.

He can be reached by phone at 413-545-2402, by fax at 413-545-1578 and by email at:

Most Common U.S. Tree Diseases & Pests


annosus root rot
anthracnose diseases
armillaria root disease
beech bark disease
brown-spot needle blight
cankers on western quaking aspin
comandra blister rust
diplodia blight
dogwood anthracnose
dothistroma needle blight
eastern dwarf mistletoe
fusiform rust
littleleaf disease
oak decline
oak wilt
scleroderris canker


Asian longhorned beetle
bronze birch borer
Douglas-fir tussock moth
eastern pineshoot borer
European pine shoot moth
forest tent caterpillar
gypsy moth
hemlock looper
Ips bark beetles
larch casebearer
locust borer
mountain pine beetle
Nantucket pine tip moth
pales weevil
pine sawfly
pine shoot beetle
pine tortoise scale
red pine shoot moth
red oak borer
redheaded pine sawfly
Saratoga spittlebug
southern pine beetle
southwestern pine tip moth
spruce budworm
twolined chestnut borer
variable oakleaf caterpillar
walnut caterpillar
western pine beetle
western spruce budworm
white pine weevil
white-spotted sawyer

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October 15, 2019, 10:23 pm PDT

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