PESTICIDES/FERTILIZERS: Shot Through the Bark

Tree injections have been around for several years, but the delivery methods continue to evolve. Manufacturers are now providing products designed for specific trees or tree health problems. These devices can inject, or “infuse,” materials at varying pressures or volumes depending on what the tree care technician is treating.

Some newer advancements are in response to the perception that tree injections can actually damage trees by wounding them. Manufacturers are also providing products that can perform injections faster, so arborists can treat more trees in less time. The increase in injection options provides tree care contractors with opportunities to expand their services while environmental awareness in the industry continues to grow.

“Larger national tree service companies and municipal governments are moving into a more defensive posture of applying pesticides just for fear of liability of soil or water contamination or pesticide drift on cars and buildings,” says Roger Webb, owner, Tree Tech Microinjection Systems, Morriston, Fla. “That’s only going to get worse, so the market for microinjections will be there and may expand.”

The majority of arborists still use foliar treatments, but environmental regulations are expected to push tree care specialists toward more systemic approaches, such as injections, says Mike Ruizzo, business manager, neonicotinoids, Bayer Environmental Science, Montvale, N.J. “Large tree care companies are very interested in tree injections because they feel pressure from environmental concerns, so this is another avenue to get the job done with minimal exposure,” he says.

MINIMAL IMPACT. More manufacturers are designing injection systems that are less invasive because of contractors’ fears that drilling into a tree’s tissue can cause damage. One such system allows tree care technicians to insert a blunt-edged needle just under the bark without entering the xylem or drilling a hole, says Chip Doolittle, president, ArborSystems, Omaha, Neb. The needle is attached to a device similar to a syringe with two handles that release the material and an opening where a bottle of injection material empties into a metal syringe. This system works on the premise that most of the tree’s uptake occurs within the cambial zone slightly beneath the bark, Doolittle says, adding that one of the system’s main advantages is that it requires less material than some other injection methods, which may need 2 to 7 milliliters of product to be effective.

“Virtually all of the uptake done by a tree is in the outer three rings of the xylem and, in most trees, the outer ring of the xylem,” Doolittle says. “If you put a chemical into the tree past this active uptake area, you’d better put a lot of chemical into the tree and hope it wicks out to the xylem area. On the other hand, if you deposit the chemical in the outer area where 95 percent of the tree movement happens, you won’t waste anything.”

A complete start-up kit costs $1,200, which includes all the necessary accessories and four bottles of tree care materials, Doolittle says. Included in the set are two needle sizes. Typically, technicians will use the ¾-inch needle except for trees with thick, corky bark, such as hemlocks, eucalyptus, cottonwoods or elms, which require a 1½-inch needle. Technicians can determine the bark’s thickness by slowly inserting the needle into a fissure of the bark until they feel resistance. If the needle penetrates farther than the length of the plug, technicians should make the injection in the fissure. If the injection tip enters at a distance shorter than plug length, technicians should perform the injection in the thicker part of the bark. When technicians don’t feel any resistance, they should use the longer tip.

After determining the needle size, technicians then punch a hole into the tree’s root flare or the base of the tree with a type of hole-punch gun that removes a bark core and create an opening that is 1/8-inch wide and ¼-inch deep, according to Doolittle. The bark core should be about the same size as the plug that the technician will fit into the hole. The plug is designed to prevent the injected material from seeping out of the orifice and keeps air and pests from entering the opening, Doolittle says. Technicians leave the plug in the tree after completing the injection. Tree growth will eventually force the plug out, he adds.

With a straight motion, the technician then inserts the needle through the plug opening. The tip will automatically stop when it reaches the injection point. The technician can then release the material by squeezing both handles, at which point a pre-measured dose of the chemical is released into the edge of the tree’s outer layer of wood. The system is designed to release 1 milliliter of material with each full stroke of the handles, but some units can be adjusted to release a ½-milliliter dose. Once the material is released, residual effects can vary depending on the type of product used. Insecticides can last anywhere from 45 days to two years depending on the product’s solubility, Doolittle says.
 
UNDER PRESSURE. Some manufacturers are selling or planning to produce higher-pressure microinjection systems that will allow arborists to perform multiple injections in a shorter period of time. “We’re looking at higher-pressure delivery to facilitate faster movement into the tree without creating cell damage,” says Nate Dodds, president, J.J. Mauget, Arcadia, Calif. “With that, we’re going to be able to put larger volumes into one individual site in a shorter period of time.”

One system currently on the market is powered by compressed air and features an injection gun equipped with a tank that can operate at 50 to 200 pounds per square inch (psi), says Peter Wild, president, Arborjet, Winchester, Mass. It’s designed to treat a high volume of deciduous trees – anywhere from 200 to 300 trees per day – such as oaks and maples. The pressure is higher than passive microinjection systems, which typically reach a maximum of 6 psi, but not so high that cellular damage will likely occur, Wild says. A technician would need to inject material at 900 to 1,000 psi to cause damage, according to Wild.

With the air-pressurized system, technicians need fewer wound sites and can perform injections in less than one minute per caliper inch. The hydraulic device can infuse 2 milliliters to hundreds of milliliters per injection site. Products injected using this system can last up to three years with approximately half the number of injection sites as other microinjection methods, Wild says.

But at $4,500 this device isn’t priced for start-up tree care companies or lower-production contractors. “It’s a high-production device, so you wouldn’t buy it if you had a plant health care program and treated a few trees a week,” Wild says. “But if all of the sudden a tree care company has to treat hundreds of trees per week for a large plant health care program, this device is like having a spray rig in your back pocket.”

This requires drilling a 7/32- to 9/32-inch hole 5/8 of an inch into the xylem, Wild says. Technicians can determine drilling depth by test drilling until they reach the sapwood and then adding 5/8 of an inch to the xylem. After determining how far to drill, the technician would then set a plug into the opening to prevent the product from seeping out and insert the needle through the plug’s septum. The technician can then release the material into the tree.

The hydraulic system does have its limitations on resin-based trees. Because evergreens have a vascular system that is 20 times smaller than deciduous trees, the trees can’t accept large volumes at such high pressures, Wild says. In this case, technicians can use a system similar to an intravenous drip. This method features tubes connected to a pump and operates at 45 psi, still higher than traditional passive methods, but low enough that the evergreens can successfully distribute the product. The equipment costs $399 and takes 10 minutes to set up, according to Wild. The tree takes five to 20 minutes to distribute the material. “It takes about one minute per caliper inch, but you don’t need to monitor it; you can move on to the next tree, so two people can do a couple hundred trees a day,” he says.

PASSING TIME. Higher-pressure systems are fast and efficient, but their higher price tags may not make them economically feasible for some contractors. Instead, they may want to consider more conventional passive systems that take longer but don’t carry such high price tags.

“The advantage of a passive system is that it’s very cheap, and you only need a cordless drill and a mallet,” Dodds says. “It’s for the smaller operator who doesn’t want to spend hundreds and thousands of dollars, and waiting time becomes a moot point if you’re providing other services.”

The passive system can be the perfect add-on service for landscape contractors because they can perform other job functions while waiting for the materials to distribute throughout the tree, Dodds says. Contractors can expect to pay $23 to $50 for materials to treat a 20-inch diameter tree using the passive method, according to Dodds.

Unlike high-pressure systems, which force the material into the tree’s vascular system, passive systems depend on the tree’s sap flow to suck the material up through the tree, Dodds says. “This is truly a systemic approach because it becomes part of the tree’s system in a more natural form,” he says. “With high-pressure systems, you force the chemical in and you risk causing damage.”

As a result, uptake can range from minutes to hours, according to Dodds. This method works by drilling an 11/64-inch-wide hole downward at a 45-degree angle 6 to 12 inches from the base of the tree ¼ to 1/8 of an inch into the xylem. The technician would then insert into the drill site a plastic tube connected to a capsule filled with material, Webb says. To secure the injection unit, the technician must gently tap the cap with a rubber or plastic-faced mallet. The technician can pressurize the unit by pushing in the cap end. When finished, the unit should be removed within 72 hours of installation.  

BIG MAC. Microinjection is effective against most insect-related problems, but diseases sometimes need a little extra punch before they’re under control. That’s when macroinjection comes into play. Macroinjection involves distributing 30 to 60 gallons of material into a tree at pressures more than 40 psi. Macroinjection also requires drilling a hole more than 3/8 inch in diameter. The holes are drilled into the root flares about 1 inch past the bark, according to Rainbow Treecare Scientific Advancements, St. Louis Park, Minn. The technician would then insert the tees by hand and lightly tap them with a small hammer. The tees are then connected to tubing that is feeding from a solution reservoir. The technician should then turn the pump on and adjust the air pressure at 15 to 30 psi. 

This is most commonly used as a preventative measure against Dutch elm disease, oak wilt, sycamore anthracnose and chlorosis, which is a condition caused by trees that don’t produce enough chlorophyll, says Tom Prosser, president, Rainbow Treecare Scientific Advancements.

A full set of macroinjection equipment, which includes needles that are attached to a harness and a pump, costs $285, Prosser says. A technician will spend approximately $100 for most materials to treat an average size tree, which is approximately 27 inches in diameter. The process typically takes about one hour to complete.

The two major advantages that macroinjection has over microinjection are lower application frequency and higher efficacy against some major diseases, Prosser says. “The other issue with microinjectors is that you have to wound the tree every single year, and that has some pretty negative consequences, whereas with this you only do it every three years.”

In fact, Prosser says noninvasive treatments, such as soil drenches, are preferable over trunk or root-flare injections when treating certain tree conditions. Contractors should be aware of each injection system’s limitations. For instance, foliar sprays usually work better against diseases such as apple scab and bacterial leaf scorch, Doolittle says. And trees with poor-functioning vascular systems or trees showing signs of stress may not respond well to injections, Dodds says. “Sometimes we’re the last-ditch effort, and there are some trees like the American beech that are very sensitive to injections,” Dodds says. “If the tree is weeping and hasn’t put a good effort into healing, then you may want to think twice about drilling into the tree and injecting.”

Doolittle agrees, saying that contractors need to have realistic expectations when dealing with tree injections, especially when communicating with customers. “If you have a vascular system that is so destroyed that you can’t do anything, I think that’s something the contractor has to watch,” he says. “They need to know the liabilities of that particular tree and can’t go to a heavily damaged tree and promise the moon."