Over the past four decades, the pendulum seems to have swung between wanting to kill any insect that might be eating a leaf or two on a tree to extreme earth friendliness. Anyone remember the flower children of the 1960s, Rachel Carson, or Meryl Streep crying over Alar? Somewhere in the midst of all of these, an awareness of the legitimate concerns over damage to nontarget insects and other organisms came to light.

Pollinators, like the well-known honeybees and bumblebees, as well as mason bees, leafcutter bees and sweat bees, are one important group that can be impacted by insecticides. Pollinators are crucial to American agriculture, with crops such as grapes, oranges, apples and alfalfa depending on their services. Closer to home, the success of backyard landscapes, veggie gardens and ornamental plantings also hinges on pollinating species.

Protecting pollinators should be as important to tree care providers as good customer service and identifying profit centers. Pollinator conservation can be as simple as reading the label and strictly following instructions regarding bees. In some cases, product selection is the key. For example, the neonicotinoid class of insecticides has recently been scrutinized for killing honeybees after a mistimed application to linden trees for control of Japanese beetles. Choosing a non-neonicotinoid insecticide and following label directions correctly will help ensure that a similar disaster is avoided.

Aside from pollinators, there are predaceous, nontarget beneficial insects, such as lacewings and ladybird beetles, that should be preserved. Smart spraying should involve consideration of the target pest as well as the ones that may be killed as a side effect. One of the classic examples of this is when a broad-spectrum insecticide is applied to control leaf feeders, such as oak caterpillars, when a specific product containing Bt (Bacillus thuringiensis) would work just as well without killing the beneficials.

Documentation of existing fungal infections can be noted and reported to the client for possible future applications. PHOTO: JOHN C. FECH, UNL

Documentation of existing fungal infections can be noted and reported to the client for possible future applications.

Unnecessary applications

There are needed and unneeded pesticide applications. As a responsible tree care provider, it’s your responsibility to know the difference. When the population of a particular pest is low, a judgment must be made whether to attribute the cause of a possible decline in the tree’s health to an insect and therefore make an application for control, or dig a little deeper to determine if the actual cause is something more than the pest. In the overall scheme of things, unnecessary applications often occur when there’s pressure from the customer to control the pest, or at least to make their sick tree look better.

If a tree is unhealthy, but less than a handful of aphids or mites are present, the tree could be struggling due to a lack of oxygen because it was planted too deeply. All the permethrin in the world won’t help in that situation. It’s quite plausible to assert that if a tree is unhealthy and the customer believes that insects are to blame, but your inspection turns up only a few insect pests, making an insecticidal application is unnecessary. Some entomologists or arborists might say that it would be fraudulent.

The real issue at hand is the concept of threshold — the number of insects that are necessary to cause unacceptable damage. Determining when the threshold has been surpassed is a skill that’s developed over time, with training and years of experience.

Honeybees are crucial to American agriculture as well as sustainable landscapes. PHOTO: JAMES A. KALISCH, UNL.

Honeybees are crucial to American agriculture as well as sustainable landscapes.


Whether you call it scouting or monitoring, regular inspection of your customers’ trees is a crucial step in the judicious application of insecticides and fungicides. There are many benefits to be realized from scouting, and here are just a few:

  • Monitoring helps stop an infestation before it takes over and causes lots of damage.
  • It helps document a current disease problem, and you can note that a preventative application should be considered next year.
  • Instead of a once-and-done approach, regular monitoring allows you to address pest problems proactively, which helps create a positive relationship with the client and also generates an income stream for your company.
  • It reinforces in the customer’s mind that every time they see the company truck it doesn’t necessarily mean that they have a problem to be fixed, just that a professional is on the property to provide a valuable service, to share their years of training and experience for their benefit. Charging a modest fee for the inspection helps underscore its value.
Before spraying, always ask: "Is economic damage caused by the pest?" PHOTO: JAMES A. KALISCH, UNL

Before spraying, always ask: “Is economic damage caused by the pest?”


Ask any baseball player, comedian or politician, timing is everything. The squeezing of the glove, the delivery of the punch line and making promises all require proper timing.

With spray applications, the time of year, the life stage of the insect, the presence of disease spores, the number of insects on a leaf, and using previous notes from monitoring are key elements for good control. The standard example is the life stage of the insect or fungus. Most insect pests and fungal diseases have only one vulnerable stage – the part of their life cycle when a pesticide application is effective. For insects such as oystershell scale, the crawler stage is most easily controlled, as the waxy covering is not in place, leaving the insect susceptible to spray applications.

Application methods

Whether using foliar sprays, trunk injections or basal drenches, each application method has pros and cons.

On the plus side, spray applications with coverage of the upper and lower leaf surfaces provide good control of surface-feeding insects and act within a few days. They also offer flexibility in several ways: (1) the entire tree doesn’t need to be sprayed, only the affected portions, and (2) they provide the option to include certain fungicides in a tank mix. On the other hand, when wind speeds exceed 5 to 10 mph, the formulation can drift to nearby property and cause damage. In addition, the personal protective equipment (PPE) that must be worn by the applicator is generally more extensive than with injections and basal drenches.

Trees struggling from girdling roots may also have a few aphids on their leaves, but they may not actually be causing damage. PHOTO: GREG HARR

Trees struggling from girdling roots may also have a few aphids on their leaves, but they may not actually be causing damage.

Injections place the insecticide product directly in the conductive vessels of the tree, which minimizes the drift potential to a large degree. In addition, trees on slopes can be treated by injection without concern that the product will move down the slope into a water body, street or other nontarget area. Drawbacks with this type of application include wounding the tree through holes in the bark and cambium, and possible diminished uptake if feeding has destroyed the xylem and phloem.

Basal drenches provide potential uptake without the worry of damage to the trunk at injection sites. Negatives associated with drenches include possible off-target movement and exposure to the applicator and family members/pets before uptake is completed.

It’s up to the tree care provider to use discretion when applying pesticides. Using integrated pest management (IPM) and monitoring pest populations is an important component of providing good tree care. Before application, evaluation of the tree’s status is helpful to determine if the economic injury level has been reached. A thorough understanding of the pest’s biology is useful for choosing the appropriate product. Insecticides and other pesticides must be used properly; consider all options when making your selection and follow the label directions explicitly. By following protocols and using smart application techniques, the industry will stand a better chance of keeping the toolbox well stocked in the future.