Scientists estimate that there are 10 quintillion insects on the planet. That’s 10,000,000,000,000,000,000 individual creepy crawlies! And, boy, do they like to eat! From early spring to late winter, it is extremely likely that someone is dining your prized plant’s leaves, stems, or roots.
Control of insects in the garden is a hot button issue. Often times gardeners are tempted to use strong insecticides as soon as they see a single bug. Hell, I’ve been known to grab a spray bottle of Sevin myself from time to time. Luckily, we’ve all gotten much more sensitive to the fact that beneficial insects are also living in and working for us in our gardens. In order to minimize the use of poisonous chemicals and the destruction of beneficial insect populations, it’s extremely helpful to know what kind of insect is causing the damage you see.
When it comes to identifying which insect is causing the problem, there are a few ways to go about it. The first is to research the plant where most of the damage is occurring. Many plants are susceptible to particular buggies. Those plants can become infested with hundreds of insects of a single type. For example, roses are well-know to harbor aphids. Every year at the nursery, I fully expect to see them by June, and begin to check all the roses for this pest. I’ve researched many different ways of killing them, but I most often use an organic method that I was taught years ago. I just put on a gardening glove and squish them! Since most of the aphids cluster on the tips of the new growth, I can easily murder 90% of the population in one go. A second squish-a-thon a week later, and the population is at such a low level that’s it hard to notice any further damage.
The second way to determine what is eating your plant is by studying the damage itself. My favorite “Bug Book” is Garden Insects of North America, by Whitney Cranshaw. This book breaks down the feeding patterns of insects into 9 categories, and gives a very extensive list with great pictures.
Keeping roses as the example, I noticed a number of holes in the leaves of some ‘New Dawn’ roses recently. I open up my trusty Garden Insects of North America and turn to Chapter Three, “Leaf Chewers”. Unfortunately, I have not seen the actual insect feeding on the leaves, so I can’t really settle on a specific pest yet. I flip to another great book in my library, The Organic Gardener’s Handbook of Natural Insect and Disease Control by Barbara Ellis and Fern Marshall Bradley, to see what insects commonly cause this kind of damage on roses. Now it becomes process of illumination. I know it’s not Japanese Beetles, because they are large, and feed during the day – I would have seen them, and the damage would have been more serious. I also rule out large caterpillars, because they also feed during the day, and leave behind noticeable droppings, which I should have seen clearly.
It’s likely that the damage on these leaves is some sort of sawfly larvae or rose chafer. Most of these leaf-eaters are already done feeding for the season, and should not cause further damage. So, in this case, I will wait until next June, and begin to pay very close attention to the leaves. At the first sign of the pest, I will apply an appropriate insecticide.
For photos of some common insects and the damage they cause on plants, check out our pinterest page:
-Brad MacDonald