The two most important things you can do to control insects in your garden and landscape are monitoring and early detection. They go hand in hand, but to be effective you need to know what to look for, where to look and what to use.
Mites can be so small that they’re virtually undetectable until serious damage has taken place. Thrips, on the other hand, may be large enough to be seen in some cases but you can’t see many of them because they hang out in places like flower buds, before they open.
There are clues though. There are almost always clues.
To keep ahead of insects in your landscape and vegetable garden you need to be observant and have a critical eye. As a matter of habit, I monitor for signs of insect problems wherever I go. That said, I think if you look too often you miss some of the subtle changes that take place over a period of days.
Take notice of clues and changes like yellow spots showing up on the foliage of a maple tree, the notches being chewed on the edges of rhododendron leafs, the shotgun-like holes in the leaves of cabbage or bean plants, or black mold growing on the top sides of the leaves of an American holly, for example.
Watch for the sticky or gummy feeling when you touch the foliage of privet leaves, tiny black gunpowder-like pellets on the upper surfaces of any foliage, stippling of foliage that leaves tiny yellow spots on a leaf that should be uniformly green, and fine silky webbing around buds that’s causing leaves to curl on themselves. Look also for curling or rolling leaves, crows or blackbirds feeding incessantly on your lawn in the same circular spot and tips of pine trees and junipers that turn brown then droop or break at 90-degree angles.
Also be aware of flowers on a rose or delphinium whose buds appeared fine but when the flowers open they are distorted and quickly discolor. Be on the lookout for buds on a peony that darken, become brown and then get fuzzy. Notice if tiny gnats fly from pot to pot on your indoor or outdoor houseplants.
More warning signs include: a cottony white mass on stems, branches or where leaves join a stem; frothy, white masses about the size of a marble on outdoor annuals and perennials; vegetables that are planted one day and the next are lying flat in the garden as if something has chewed, sawn or cut the stem off just above the ground; and sawdust on a twig or stem of a tree.
Every single one of these is a clue, the telltale signs of insect problems in process. Most of the ones I’ve noted are pretty classic and can easily lead you to the problem. Some are particular to specific plants (such as what might be happening with your rhododendrons right now); we call those host-specific insects. But some can occur on a wide range of plants, such as the spittle that we’ve seen this year on roses, day lilies, phlox, yarrow and a range of other garden plants that the spittle bug has hit this summer.
The knowledge you can gain from a little bit of reading can be quite enlightening because you’d know that the issue with the rhodies, for example, could be a very serious one that could take several years to remedy. At the same time, though, you’d know that the spittlebug, and it’s spittle, can easily be dislodged with a simple spray of water.
At this time of the year you should be walking through your landscape at least a couple of times a week. Train your eyes to look at more than just flowers and fruits. Look at the stems, twigs and foliage as well, all the while keeping in mind that for the most part insects inflict their damage by either chewing, sucking or rasping. These three categories come in handy later on as well because controlling many insects can be dependent on the manner in which they dine (or devour).
Are you watching your rhododendrons for signs of damage to their leaves? One of the most notorious insects that feeds on rhodies is the black vine weevil.
If you wait to see the weevil you may wait a long, long time. They’re nocturnal and live mostly in leaf litter and mulch until they come up to feed—where they form the characteristic leaf-edge notches. While we most often notice their damage on our rhodies, they are not host-specific, and also feed on hemlock, mountain laurel, Japanese holly and several other plants.
The leaf notching is rarely extreme. It’s really the larval, or grub stage, of the weevil that can actually kill landscape plants as they feed on the roots causing the above-ground parts of the plant, the shoot system, to collapse as the weather gets warmer.
I recently was asked to look at some shrubs on a small property in Southampton. There was something strange going on that the arborist and landscaper had written off to watering issues. While the watering issue may have been some of the problem, there was something else going on and the clue was pretty obvious.
Many of the leaves had a sooty black cast to them. Most plant people would immediately recognize this as sooty black mold. The mold is nearly always present on our landscapes but when it comes into contact with what we call “honeydew,” the sweet excrement of sucking insects, the sooty black mold takes hold and begins to blacken the foliage.
So, what do you do when you find sooty black mold? Why you look it up of course.
Look up to the foliage above and examine the undersides of that foliage. Sure enough, on the leaves above there will be some telltale spots. A simple jewelers 10X loupe can be used.
Sure enough, at the Southampton property, scale was all over the place. All it took were a few clues and a quick look for the mystery to be solved.
This is not to say that the scale problem was solved, as that’s still another challenge, but at least we figured out that in addition to the watering issues the scale was slowly sucking the life out of these plants.
Insects are not always problems. Your landscaper may say he’s found grubs in your lawn, therefore he has to chemically treat the lawn. But a few grubs are pretty normal, in some cases even a half dozen or more per square foot of lawn is acceptable.
Sometimes an insect is not really a problem on some plants, but then disastrous for others. Take the leaf miner for example.
Leaf miners on columbines can be unsightly but they are nearly impossible to eradicate and aren’t really damaging to perennial plants. Since they are just unsightly and not really damaging, why try to get rid of them?
On the other hand, leaf miners on boxwoods can be both unsightly and permanently harmful. Here, we need to take action.
Being forewarned and forearmed is also a good thing. Cutworms in your vegetable garden can play havoc on a number of crops, cutting them down long before they even get established.
You can use chemicals to control them, but it’s much more sensible (if you’ve had cutworm problems in the past) to use cutworm collars on the plants the next time. No chemicals needed.
When it comes to rose plants, there are three different beetles that can cause issues: Japanese, Oriental and chafer beetles. You can spray the beetles from late June through August, but at the same time you’ll be killing every beneficial insect in your garden. Think about using other methods to control the beetle grubs in the ground so they never mature into those hungry and voracious terrors.
Bottom line, know your bugs. Learn which are raspers, chewers or piercers.
Each is controlled differently, each does different damage and each has a different life cycle. Knowing what that cycle is can be the key to control with as little environmental harm as possible. Be a responsible gardener. And as always, keep growing.