A question I get frequently during the spring and summer months is, “What’s been eating my plants?” This is not always an easy question to answer. Beyond the evidence that something has indeed been munching on your ornamentals, more clues to what did it are needed.
Animal or insect? Animals like deer and rabbits often leave traces like hoof or paw prints or piles of fecal pellets. Where is the damage located? Deer are browsers; they eat young tree twigs so look for damage along the outside of the planting at about chest height. In contrast, rabbits tend to move into the planting before feeding. They are shorter than deer so the damage will naturally be closer to the ground. However, just because your Hostas were eaten does not automatically mean that the rabbits did it. The most conclusive evidence is to catch the animal in the act.
Discouraging animals like deer and rabbits is a whole industry in itself. There are many solutions such as mechanical scaring devices; sprays of egg albumin, blood or predator urine; and home remedies such as human hair – all claiming to keep the animals away from your plants. My experience is that any animal can get used to things once they realize that there is no actual threat. Changing your deterrents from time to time should help discourage the deer and rabbits by keeping them alarmed. Of course, having a dog around wouldn’t hurt.
On the other hand, what if the damage is not whole sections of missing plant material, but simply holes in the leaves? That seems more like insect damage. But what kind of insect did it? Again, the surest way to find out is to catch the culprit in the act. Smaller insects, such as flea beetles, usually feed on the leaf tissue between veins, which is thinner and easier for them to eat with their small mouthparts. Larger insects do not suffer from such limitations so they eat the entire leaf, veins and all. Two insects that fall into this category are grasshoppers and caterpillars.
Grasshoppers feed on grasses, sedges, vegetables, ornamentals and many other plants. These large insects are relatively easy to identify by their strong hind legs and over-sized heads. They depend on their green and brown coloring to camouflage them from predators, irate gardeners and avid fishermen.
The life cycle of grasshoppers involves incomplete metamorphosis. This means that the eggs hatch into nymphs, which look like small adults. The nymphs grow and molt five or six times before becoming a full-sized adult. The visual differences between nymphs and adults are size and wings. That’s right - in addition to being incredibly strong jumpers, grasshoppers can fly. Well, all right they don’t fly very well but they do fly. That ability makes them even more difficult to catch and increases their feeding range. Most grasshoppers make nuisances of themselves during the summer. Closely related to crickets and katydids, grasshoppers share their method of making “music” by rubbing their rear legs on their abdomens or on their stiff forewings.
Grasshoppers have a number of natural enemies; praying mantids, frogs, robber flies, birds and even coyotes have been known to enjoy a good grasshopper steak. There are also numerous parasites; fungi and nematodes that help control the population. If those measures fail, insecticides such as acephate, carbaryl and permethrin have proven effective at controlling them.
Another insect that can be classified as “large” (depending on the species) is the caterpillar. Caterpillars are as varied as the butterflies and moths that they eventually become. Their colors and patterns can be quite beautiful, but it doesn’t make up for the fact that they are plant eaters – like grasshoppers. However unlike grasshoppers, moths and butterflies have a life cycle of complete metamorphosis.
Butterflies and moths often lay their eggs on the undersides of leaves. The caterpillars that hatch from the eggs will grow and molt several times until their final size is reached. At this time, they either spin a cocoon or form a chrysalis within which they can pupate. After pupation, an entirely different creature emerges – the moth or butterfly.
When investigating plant damage, “window paning” on the plant leaves in addition to holes of increasing size usually indicates the presence of caterpillars. Larvae begin feeding immediately after hatching, but since they are small at this stage they are unable to chew all the way through the leaf. This leaves a translucent layer of tissue (a “window pane”) that quickly dries out, leaving a brown patch on the leaf. As the insects grow, they spread out to other leaves and feed in earnest, often eating entire leaves.
Here we have a conundrum. Most people like butterflies. Entire gardens are planted specifically to attract them. Moths and butterflies are pollinators and so are beneficial insects. However, the larval forms of these marvelous creatures eat plants and reduce their aesthetic appearance. What to do?
The good news is that caterpillars rarely kill plants. Most of them eat without causing significant reduction in the plant’s aesthetics. And there are plenty of predators around to help keep their population to a reasonable number. If you decide a higher level of control is warranted, then controlling them early is best. If there are only a few caterpillars, they can be picked off by hand and disposed of (I throw them to the fish). For larger numbers, insecticides work well, especially pyrethroids.
Of course, there are many other things that eat plants. I have touched on just a few that can eat a lot. If you cannot figure out what is causing the problem and it drives you crazy, you might consider surveillance cameras with night vision.