By Erik Gabbey
As our understanding of pest control has progressed, the number of tools available has grown considerably. Whereas arborists once had only sprays and saws as tools, they now have soil-applied systemics, systemic bark sprays, and trunk and root injections. Benefits of systemic insecticides include a broad range of uses, ease of application, complete canopy coverage, and limited environmental exposure. This is possible because of the way these insecticides work: Systemic insecticides use the tree’s own vascular system to move the chemical throughout the above-ground trunk, limbs, and leaves. As a result, when applied correctly, the chemical reaches even the highest leaf, something that is difficult to manage with spray applications.
Photos provided by Rainbow Treecare Scientific Advancements
Systemic bark spray
For systemic bark sprays, an insecticide solution is sprayed on the bark of the tree using conventional spray equipment. Only the lower portion of the bark is sprayed — generally just the lower 4 to 5 feet of the trunk — unlike a foliar spray, which is used to cover the entire canopy. The product is absorbed through the bark and translocated, sometimes with the aid of a surfactant.
Trunk and root injection
Tree injections are slightly more complicated, and require an infusion system, but begin controlling insects almost immediately. There are several options on the market, but most work in a similar manner. After drilling small holes in the trunk or root tissue, a chemical solution is injected under pressure. Using the tree’s natural transpirational pull, the product moves upward throughout the tree’s canopy. Tree injections come in handy when soil application isn’t possible (for example, when pavement surrounds the trunk of the tree, or if the tree is growing near a body of water).
It’s great to have easy and predictable application methods, but what insects will they control? After all, if the chemical only controls a narrow range of pests, how useful is it? Let’s look at some of the major categories of insects and some examples of systemic insecticide control.
Adelgids and scales
Adelgids and scales have what are called piercing/sucking mouthparts, which they use to siphon water and nutrients from their host plant. In the past, these insects have been difficult to control because they tend to obscure themselves on the plant. Some adelgids can induce gall production in host plants, and end up living inside these structures. Others, like Hemlock Wooly Adelgid, will produce white wooly masses as defense. This obviously makes them difficult to control, and though horticultural oil as a spray is still part of the treatment plan, systemic insecticides are now the primary tool. For these particular pests imidacloprid and dinotefuran are highly effective.
Imidacloprid may be applied via the soil as an injection or a drench, or injected directly into the trunk. Imidacloprid is especially useful because it degrades relatively slowly, and provides protection for up to an entire year. This means that treatment windows such as those targeting a specific life stage can be expanded, making control more operationally friendly. Dinotefuran is another useful active ingredient, for slightly different reasons. It can be applied in the soil or as a bark spray. Because of its high water solubility, the tree takes it up and distributes it very quickly, often providing protection in only a couple of weeks, and thus giving applicators an emergency or just-in-time treatment option. However, this solubility means that it does not persist as long as imidacloprid in the tree. These two chemicals can be used in concert: the dinotefuran can be utilized in the short run to provide quick pest management, and imidacloprid used in the long run to provide a year’s worth of control.
Systemics also provide reliable control for foliar feeders. This group of insects includes leaf beetles, leaf miners, and caterpillars, to name a few. As the name would imply, these insects feed on the leaves, and are exposed to chemicals applied as a spray. So why not just use a spray application to control these feeders? Two reasons: Sprays only remain effective for two to four weeks or so, meaning timing must be perfect; and all leaves on the tree must be treated to provide control. As mentioned earlier, both of these issues are solved with systemics.
One of the key chemicals for combating leaf feeders, including leaf-feeding caterpillars, is acephate. This chemical provides control for a group of insects known collectively as lepidopterans, which includes insects whose larvae will become moths and butterflies in adulthood. Imidacloprid and dinotefuran have not been effective against this group, but acephate has succeeded where the others have failed. Acephate can also be used for some of the other pests in the foliar category, such as some species of leafminer. As for leaf beetles, imidacloprid and dinotefuran are both used commonly. There are several tree injection formulations of acephate, and there is a soil-applied acephate formulation labeled by the EPA as well.
No discussion of systemic insecticides would be complete without mentioning two of the headlining insects we are dealing with today: Asian longhorned beetle and Emerald ash borer. These two insects are invasive in the United States and have caused an incredible amount of damage to municipal and forest trees. Both of these insects are in a group commonly known as “borers,” meaning they feed under the bark in the vascular tissue. This is a very important distinction, because while inside the tree, borer larvae are protected from traditional contact sprays. Although there are spray treatments that are effective, such as bark and limb sprays to prevent infestation, systemics are preferred when controlling these insects. In the case of Asian longhorned beetle, the city of Chicago along with APHIS used systemic-applied imidacloprid as a major control. It was the use of this treatment, along with sanitation and other practices, that led to the eradication of the beetle in Chicago. For both of these pests, soil drenches, soil injections, and trunk injections are all viable treatment methods.
Insecticides have come a long way, and the toolbox for managing these pests has expanded; there are more tools today than ever before. Systemics provide a flexibility that has revolutionized the way arborists manage many pests. Systemics work in a unique way, treat for many insects and insect groups, and greatly widen the treatment window. All of these benefits mean faster, more complete, and more accurate treatment options for today’s arborist.
Erik Gabbey is a technical writer for Rainbow Treecare Scientific Advancements and provides technical support in arboriculture to arborists across the nation.