How to Tell What's Eating Your Garden Plants

A favorite morning ritual for many gardeners is to head outdoors with their coffee and check on their tomatoes and squash or flowers and shrubs. It's the gardening version of scanning the overnight Twitter news feeds or catching the morning news on TV. There’s comfort in knowing the world is still there.

What's not comforting is to find that part of your garden disappeared while you slept. Suppose your morning jolt is not from caffeine but from discovering leaves that looked fine yesterday were munched on overnight? Or from realizing that flower buds you've been waiting to open are completely gone? Or from wondering why the tomato you were giving one more day to fully ripen is no longer on the vine?

Your first instinct is likely to nuke everything with chemical pesticides. However, there's a better option for you, your plants, and the soil in which they grow. Invest a little time to find out what's eating your plants and what — if anything — to do about it.

One mistake homeowners can make is to immediately blame plant damage on bugs. In fact, the culprit may be Bambi or Bugs.

There's a way to tell whether the cause of the problem has four feet, six feet, or 100. Look at the leaves. That's where all pests leave a telltale signature. When you learn how to read their signatures, you'll know who to blame and what to do.

Deer

The signature for deer, for example, is jagged edges on leaves and stems. Deer have small teeth on their bottom jaws but a hard palate without teeth on the top. As a result, they tear off plant parts rather than bite cleanly through them. In addition, the damage they cause is well off the ground. Another deer signature, if the ground is soft, is hoof prints.

Rabbits

The signature for rabbits, on the other hand, is a stem bitten off cleanly at a 45-degree angle. That's because rabbits have very sharp teeth. Not surprisingly, the damage they cause occurs close to the ground. Other rabbit signatures include two things they frequently leave behind: branch clippings and/or pea-sized droppings. In winter, rabbits may leave another signature called girdling. This occurs when they eat the bark completely around the bottom of a tree or shrub, which can kill the plant.

Deer and rabbit repellents, like Liquid Fence, are available at garden centers. Additional homemade deer controls, other than growing what they won't eat, include shaving off slices of bath soaps and spreading them around the garden or placing human hair among your plants. Rabbit controls include mesh fencing or netting and pop-up type plant tents.

If telltale signs on your foliage don't match those of deer or rabbits, then it's a safe bet the uninvited diners are insects. In that case, William G. Hudson, an Extension entomologist with the University of Georgia knows your pain.

But, before you grab a can of insecticide, Hudson says it's important to realize that "Most insects are either beneficial or neutral visitors." For that reason, he implores homeowners to enjoy most insects as "backyard wildlife" — an idea he admits with a chuckle that he has been struggling to sell for 30 years — as a way of not killing the "good guys." Knowing, though, that most homeowners will enjoy their plants a lot more if they haven't been munched on, Hudson, whose specialty is ornamentals, offered some tips about what to do when unsightly damage becomes too much to bear.

The first step, Hudson says, is to understand that there is an almost countless number of creeping, crawling, slithering and flying insects that inevitably can and will show up in any home landscape. Because many insects can attack a variety of plants, he advised homeowners to develop a control plan directed at insect groups based on their leaf signature rather than trying to identify and control specific insects. He divides insects that attack ornamentals into five groups, which he puts in layman’s terms.

Leaf Chewers

Their signatures are holes or jagged edges in leaves. Pests include caterpillars, grasshoppers, and beetles. Control plans depend on your goals and the size of your operation, Hudson says. Many of the caterpillars in home gardens are the result of night moths and aren't the real target of a pollinator garden in the first place, he says. If you aren't squeamish and have the time, you can pick them off by hand and drop them in a bucket of soapy water. If you must use an insecticide, organic sprays are available at garden centers.

Sap Suckers

Their primary signature is a stipling effect that blanches the color on the upper surface of leaves. That's because these insects are liquid feeders that puncture leaves and suck out the juices. These bugs can populate oaks, maples and tulip poplars where they feed on a high volume of sap that is relatively low in the concentration of some important nutrients. They make up for that, Hudson says, by processing lots of liquid and passing the excess water and sugars out as "honeydew." This, he says, is the shiny, sticky stuff that coats objects below, understory plants, and even metal objects such as lawn furniture or cars and trucks.

An unsightly sooty mold can use the honeydew as food and grow on it, which will turn objects on which the honeydew has landed black. Other examples of sucking insects include scale, spider mites, whiteflies, azalea lace bugs, and stink bugs. Soaps and oils are effective on the small, soft-bodied pests in this group (aphids, whiteflies, scales, and spider mites) but not the larger ones such as stink bugs. You will need an insecticide for those, Hudson added.

Borers

Their signatures are the holes they leave behind in the stems of woody plants such as trees and shrubs. Examples of these insects include certain types of beetles and caterpillars. Their damage is especially harmful, Hudson says, because they kill plants rather than leaving them just looking unsightly. Because borers most often attack plants under stress, the best offense is a good defense — keep plants as healthy as possible by avoiding stresses such as not watering during droughts or accidentally wounding plants while pruning, which can invite attack from clear-wing moths. There are no effective treatments after borers are in the plant.

Root Feeders

The most obvious signature is holes in corms that hug the surface of the ground in plants such as iris. An example of a pest that feeds on roots at or below the soil line is grubs, the immature stage of beetles. Here again, good culture is the best way to keep grubs and other insects from eating the corms. Hudson suggested digging iris up every few years and thinning out the beds, moving extra plants to new beds, or sharing them with friends. If you must spray, commercial ground drenches are available.

Alton N. "Stormy" Sparks, Jr. a professor of entomology at the UGA Tifton Campus, also recommends treating insects as groups when trying to control them on backyard edibles. That’s because, he says, as with ornamentals, pests have a tendency to show up on multiple edible crops rather than a specific crop.

Here is how Sparks groups insects on edibles and steps he suggests to control them.

Caterpillars

As with ornamentals, these chewing insects damage leaves. You can pick them off and dispose of them as with ornamentals or use a commercially available organic spray containing Bt (Bacillus thuringiensis), a naturally occurring bacterium that is fatal to feeding caterpillars. Entrust is an organically approved insecticide that is highly efficacious against caterpillars. "It is one of the few organic products that has the efficacy of the non-organic products," Sparks says.

Stink Bugs

The signature of these fruit-feeding insects is spotting on fruit, such as yellowish to whitish cloudy spots on tomatoes. Other favorite targets in home gardens are sweet peppers, okra, sweet corn and beans. Another signature is their ability to hide, which makes them difficult to see.

These are the most difficult insects for homeowners to deal with on edibles, Sparks says. Sparks recommends sprays containing pyrethrum, which is the strongest insecticide allowed under National Organic Standards guidelines. Pyrethrums, however, break down very quickly when exposed to sunlight. The next step up from there, Sparks says, is pyrethroid insecticides, which are synthetic and not organic.

Aphids, Thrips, Spider Mites, and Whiteflies

The signature of these sucking insects is yellow, curling, and distorted leaves or a black growth on the leaf surface. "If you don't have a large garden, sometimes you can do a good job of controlling them by hitting the plants with a strong spray of water and just knocking them off the plants," Sparks says. If you want to use something stronger, Sparks suggested insecticidal soaps and highly refined oils (not a dormant oil). If you choose this option, he says to be sure that the spray completely coats the insects. This is important because soaps and oils basically suffocate the pests. Soaps and oils, however, do not have a residual effect. They are contact sprays and you will need to spray more than once to kill new insects that hatch from eggs or new arrivals to your garden.

An important point with any insecticide is to check the package label to be sure the plant you want to treat is covered by that product, Sparks says. Labels will also advise about not just frequency of intervals to spray but also pre-harvest intervals, he added.