By Brandon Gallagher Watson
Plant health care (PHC) practitioners are faced with many questions when treating their woody patients:
* What pest are we combating?
* Is this the right time of year?
* Is this a plant health concern or just an aesthetic one?
* Is this preventive or therapeutic?
* What active ingredient are we going to use?
* Which formulation should we use?
* How long of a residual effect will I need?
* What is this going to cost me and my client?
* What application method are we going to use?
PHC managers will find that knowing the answer to the last question will go hand-in-hand with answering the preceding questions.
Strictly speaking, there are three separate application methods for PHC managers: spray application, soil application, and vascular injection. Each has advantages and drawbacks so it is important to keep your options open. As the saying goes: if your only tool is a hammer, then all of your problems start to look like nails. Being able to offer all these services to your clients will allow you to be a complete PHC company.
Spraying can be applied to the leaves or to the woody parts of the plant (trunk and limbs). Spraying has traditionally been seen as the first line of defense for the PHC practitioner. However, these days it is also the most controversial. The benefits of a spray program are fast efficacy (often spray insecticide formulations are “knock-downs”) and low product cost as they are diluted in large volumes of water. For some foliar fungal diseases spraying may be the only option for control.
The downside of sprays includes effects on non-target species, high equipment cost for modern spray rigs, drift and applicator exposure, difficulties of reaching high canopies, short residual, and the increasingly controversial nature of spraying. New laws and ordinances restrict tree spraying in many in urban areas, and there is a heightened public sentiment against this technique. That being said, if sprays are used judiciously, they still have a place in the PHC toolbox.
Systemic products applied to the soil are amongst the most operationally efficient available to the practitioner. These can be applied at the base of the tree, either by pouring a basal drench solution around the tree or by using soil injection equipment. To the tree, these methods are indifferent; the difference is to the applicator. If one is treating several trees at a site with the same product then a soil injection using a large batch of ready-to-use solution may be the fastest option. A soil drench may work best for small numbers of trees scattered across many locations.
Many practitioners will employ a dripline or grid pattern application under the tree but research has shown basal applications to be as effective or better, and markedly easier to apply. The upside of soil applications is that they are easy to apply with no chemical drift and they have a wide application window. Wounding the tree is not necessary and you get long-lasting residual with many chemistries. The downside of soil application is that they cannot be used in areas of high water tables, and you need planning: most soil-applied systemic products take weeks to months to reach the canopies of large trees.
Soil applications are ideal for preventative treatments in the fall or spring but may not be the best option for the client who calls in midsummer with insects feeding on his/her tree right now. In that case, you can use one of the other treatment options and then set them up on a preventive treatment schedule for the future.
Tree injection is a PHC tool by which chemicals are delivered directly into the tree’s vascular system using various equipment systems. An important item to remember with tree injections is that all techniques involve wounding the tree in one way or another and thus should not be used as repeated annual treatments. Injections have their place with certain chemistries that cannot be delivered any other way, most notably fungicides for vascular wilt prevention.
With insecticides, the practitioner has to ask if there is another, non-invasive manner for treatment at this time. If this is a preventive treatment, consider soil application. If the pest populations are high and the tree is in dire straights, injection offers fast efficacy at fairly low cost, but should not be the only tool in the box.
The upside of tree injection includes fast efficacy and relatively low costs, as well as limited applicator exposure. The downside is tree wounding and time waiting for uptake. With injection systems it is paramount to understand the basics of tree biology so you can perform your applications in a manner that is safe to the tree and efficacious against the target pest.
All of the above techniques have a role in plant healthcare management. Much more important than the chemistries and the methodologies is your ability to read through literature, research, and marketing claims to make decisions based on sound arboriculture. Your clients are looking to you to choose a treatment that considers the tree’s health, the environment, and one that won’t break their bank. Offering the full toolbox will allow you to get the job done right and build the trust for future business.
Brandon Gallagher Watson is plant healthcare specialist at Rainbow Treecare Scientific Advancements.