How To Safely Use Pesticides In The Garden, Part I

Last summer, I wrote a couple of columns on the types of sprayers that are available for homeowners and gardeners to use on their properties, and how to care for them and use them safely. A few readers wrote that they appreciated the advice but thought that I also should have written about how to safely use the pesticides that go into these sprayers. I agreed and said that, this summer, I would write a column on the topic—and then I saw something that drove it home. Up until just a few days ago, it had been cool and wet, though, and there’s been little need to do any spraying. Or so I thought.

As I was heading home for lunch one gloomy day last week, I passed a home where a landscape laborer was spraying a material from a backpack sprayer onto a grassy slope. The slope gradually led to a small stream that drains into a small pond.

It had rained the previous night and, due to the clouds and high humidity, the landscape remained wet. Shrubs glistened with moisture, and if you were to walk across the lawn, your feet would have gotten sopping wet.

But the laborer continued his methodical path, back and forth, up and down, spraying. He appeared to be unsupervised, and I imagined that his boss simply helped him fill the sprayer tank and gave him the most rudimentary instructions to spray.

I presumed he was spraying a herbicide to kill the weeds in the lawn—but I knew that, since the lawn was wet and rain was expected, the material being sprayed would have virtually no effect, either never adhering to the weed foliage or getting washed off by the imminent rain. Worse yet, because of the slope down to the stream that led to the pond, rain would carry the sprayed material directly into the water.

I see these errors in judgment (and management) all too often.

First, though, let’s agree on what a pesticide is. The term encompasses any material that’s used to kill weeds and insects, but pesticides also are used to kill rodents, slugs, fungus and other things that we include in the general category of pests.

The pesticides that are available to us in 2017 are very different from the ones we could buy just a decade ago. They are safer for us and safer for our environment. But the term “safe” is relative, as even these newer, less toxic pesticides can be misused and abused, and can cause great environmental and personal harm.

Gone are the days of most chlorinated hydrocarbon-, organophosphate- and carbamate-based pesticides, which were killing us along with our pests. What we find on the shelves at the garden centers now are botanical insecticides, biological insecticides and organic herbicides, as well as new classes of horticultural oils and herbal extracts that can be highly effective.

Gone also are the days when you could spray a pesticide and its residual effects would continue to kill for days, or even weeks. Those long-acting pesticides were referred to as “persistent,” but more often than not if they were persistent in their ability to kill insects, they also were persistent in our bodies and food supplies.

But don’t be lulled into a common complacency that can equate “organic” or “botanical” into an assumption that the material is harmless. Many of these new products are what we refer to as broad spectrum pesticides. They may not kill people or pets, but their broad killing ability among the insect populations means they will kill both the target insect—such as a Japanese beetle—but also the beneficial insects, including honeybees.

Pyrethrum is a good example. Derived from a species of African daisy, it’s great on a wide range of insects that can damage your plants; it kills almost immediately on contact and degrades and becomes harmless in hours in sunlight. But it’s highly toxic to honeybees.

Neem oil, on the other hand, an extract from the neem tree bean, is much less toxic to bees. The downside to neem oil, though, is that it’s not effective on all insects, so you need to know what you’re spraying for (the target) and what least toxic pesticide will work on that target.

So, pesticides refer to those materials that we use primarily to kill weeds and insects. That weed or insect is called the target. The object is to find the least harmful pesticide that will reduce or eliminate the target.

You can do this by going to the garden center and telling the salesperson, “I’ve got a bug on my roses, and I need to kill them.” Hopefully, the salesperson will ask questions like, have you seen the bug? What’s the bug doing? Are you sure you need to get rid of it? If it’s as simple as an aphid, your solution could be as simple, and as safe, as an insecticidal soap. But if it’s a rose chafer, or Japanese beetle, things get more complex.

Next week, I’ll get into very specific details on how these pesticides work and how to use them safely. But as part of this primer, you need to know how to use a process that we call integrated pest management, or IPM. Practicing IPM will reduce your need for using pesticides, will allow you to use the least toxic materials and will reduce the causes for these pests.

The first step is in learning how to identify the pests; in this case, weeds and insects. There are only about 10 weeds and 10 insects that make up the critical pests in our gardens, and you can easily find them in online keys and articles.

The next step is to learn prevention and exclusion. We’ve gone over the fact that a healthy lawn is the best way to exclude weeds, and one of the best ways to reduce garden insects is to ensure that you take care of the naturally occurring beneficial insects.

A great example of this is with the scale that’s nearly decimated our beloved privet hedges. We know that on properties where broad spectrum insecticides are used, the beneficial insects that feed on and can control this scale are killed. Switch to a different insecticide, like an oil, and, as if by a miracle, the predatory insects that feed on the scale return. IPM.

Another critical aspect of IPM is referred to as monitoring. It’s as simple as going out into your landscape and looking for weeds or insects on a regular basis. There are even tools like GDDs, or “Grower Degree Days,” that can allow you know on almost the exact day when a particular insect will show up. Get rid of it soon after that, and you may solve your problem for the entire season. Again, your best tools here are a key to weeds and a 10x magnifying loupe so you can look for the bugs.

IPM focuses on prevention. Just about every reputable landscaper knows about it, though not all use it. You can and should.

In the meantime, take a few minutes to read the label on your bottle of insecticide or bag of herbicide. You may need a magnifying glass, but the information on that label is your guide to safe and effective use of these products.

Next week, the nitty-gritty to safe use, and how these materials work, and don’t.

Keep growing!