By Brandon Gallagher Watson
Arborists are increasingly asked to provide “greener” alternatives for tree health care, but what does that mean, and what options are available for professionals? Does “going green” simply mean we have to swap out synthetic chemical treatment “A” for organic chemical treatment “A?” Can green arboriculture be part of the toolbox without sacrificing efficacy and economics? As you will see, green tree care can be many different things, including just slight changes to practices you may already be doing.
Agricultural IPM versus urban IPM
Agricultural producers have nearly all gone toward some form of Integrated Pest Management (IPM) practice. IPM uses a combination of monitoring, cultural practices, prevention and control to manage the pest populations of their crops. One of the overarching themes of IPM is setting action thresholds, usually based on the economics of a plan implementation. Prior to any pest control measure being applied, IPM managers determine the injury threshold, the point at which a pest population will become enough of a threat to the crop where it makes more sense to control the pest than allow it continue to do damage. They then set action thresholds lower than this so a management intervention can occur before the damage is economically significant. For deadly, invasive issues such as Dutch elm disease or emerald ash borer, an arborist can employ a similar model for determining the necessity of a management action. It is often less expensive to treat a tree and have it live than allow the tree to die and cut it down.
The arborist’s job can be a little more challenging when the injury thresholds are determined by aesthetics rather than economics. Japanese beetles can seriously impact a tree’s health if populations are significant; however, the vast majority of leaf beetle infestations are more unsightly than deadly. In these cases, the client’s individual tolerance for damage will set when a management action should intervene. If the client has a very low threshold for damage and wants every leaf perfect, the tree health professional may employ a preventive treatment to ensure as little damage as possible. If the client has a higher tolerance for damage, the professional may suggest monitoring the population and not implementing a control strategy until the problem becomes critical enough that it is no longer an appearance issue, but a significant health issue.
Organic versus natural versus green?
When it’s decided that a management action should be taken, there are more options available than ever, but there is also more confusion. Arborists seeking “green alternative” treatment options find claims such as “organic,” “natural,” and the aforementioned, and incredibly ambiguous, “green alternative.” But what do these titles mean? Of these, “organic” is the most strictly defined. To label a product as “organic,” it must be non-synthetic and pass independent review by the Organic Materials Review Institute (OMRI). Certified Organic agricultural producers are restricted to only use pesticides that are OMRI listed, and there are more than 2,100 currently listed options. Arboriculture does not have a defined “organic certification” equivalent, but there are certainly clients who are interested in an organic approach, and many tree care companies are promoting organic treatment services. Although there are certainly fewer options available compared to agriculture, arborists can still seek out organic-labeled treatments.
“Natural” products don’t have the same rigid definitions but it can be generally assumed that a product claiming to be “natural” is derived from some natural source. This can be anything from botanical-based products, mined products, or even fermented products. There is sometimes confusion between “organic” and “natural;” but the main difference is all organic products are natural but not all natural products are organic, as the latter had to meet specific criteria, as well as have a large enough agricultural market potential for a manufacturer to seek the certification. “Green alternative” products have the vaguest definition, and can be anything from narrow-spectrum active ingredients to different application methods. Broadly speaking, green alternative options will have softer impacts on the environment than other options, but may not be technically “natural” or organic certified.
A biorational approach
Biorational management tools can be even broader in definition than “green alternative.” This can include everything from encouraging predatory insects or parasitoids, planting disease-resistant varieties, or even using one application method over another. Systemic tree health treatments, whether soil drenched, soil injected, or tree injected are all considered to be part of a biorational pest management approach. In fact, many view the advent of systemic arborceuticals (medicines for trees) as one of the great leaps forward in biorational arboriculture. When compared to the previous industry standard of spraying for every tree health issue, systemic treatments use significantly lower volumes of active ingredient, applied to a much smaller area, and, as the treatment moves up through the tree, only targeted pests are exposed, greatly reducing the effect on the surrounding environment and non-target organisms. Soil applications, applied right at the base of the tree, use a very small volume of active ingredient and, when used as labeled, have a minimal environmental impact but should not be used in areas with high water tables. Tree injection, which puts the treatment directly inside the tree, can further reduce the exposure to the environment when soil applications are not an option.
Even spray applications have a place in biorational tree health management if the right treatment is being employed. Famous examples of biorational treatments, such as the use of Bacillus thuringiensis (Bt), can only be applied by spraying. Bt is a bacteria that is widely used in the management of lepidopteran species, such as gypsy moth, as it only will affect larvae of the moth and not other beneficial insects present. Other strands have been developed that control flies, mosquitoes, and leaf-feeding beetles such as elm leaf beetle. The upside of Bt is, as mentioned, the narrow spectrum of insecticidal activity, while the downsides include a short window of efficacy, expense of the treatments, and the necessity of spray application. Other effective biorational treatments that can be spray-applied include spinosad, a naturally occurring insecticide produced via fermentation of the soil bacteria [ital>Saccharopolyspora spinosa<ITAL], P arborist.
A truly integrated IPM
Part of an effective IPM plan is preventing the problem to begin with so that a pesticide is not needed. Insects and diseases tend to affect weakened individuals so keeping trees healthy and happy with proper watering, mulching, fertilizing and site selection can go a long way toward reducing the use and impact of pesticides in the urban forest. Knowing the lifecycle of the pest and employing proper timing for management is one of cornerstones of effective IPM, so know your pests, your treatment options and your timing to be the most effective pest manager possible. For the arborist looking to employ the greenest management plan they can it is more than just subbing out one pesticide for another. It is about knowing the biology of the pest, the tree, the toolbox of treatment options available, and, perhaps most importantly, the needs and concerns of the tree’s owner. Knowing all of these can help turn “green” tree care into the green arborists are looking for — in their wallets.
Brandon Gallagher Watson is communication director at Rainbow Treecare Scientific Advancements, and is an ISA Certified Arborist (#MN-4086A).