What’s Eating My Plant?

Cathy Kavassalis – Halton Region Master Gardener

Many arthropods (insects, mites, etc.), gastropods (slugs and snails) and mammals (deer, voles, groundhogs, etc.) feed on plants. Some of these do this at night making it difficult to know which animal is doing the damage. Some are well camouflaged and hard to see. Others hide under leaves. Others feed and then fly away. Still others are so tiny that they are easy to miss.

We gardeners don’t like to hear this, but if nothing is eating our plants then something is very wrong in our gardens. Our plants are part of foodwebs.
C. Kavassalis

Before taking any action, look closely at your leaves. Peak under the leaves, paying attention to the veins. Some herbivores drop to the ground when startled, so check the soil. Check outside in the evening with a flashlight for nocturnal nibblers. The kind of damage you see can help identify the type of herbivore. When large chunks of plants are missing, suspect large mammals like deer or porcupines, etc. Look for tracks, tooth marks, holes or excrement to ID the culprit.

Four-Lined Plant Bug, Thrip, Leaf-Cutter Bee

Many chewing insects like beetles, grasshoppers and crickets that can fly or hop may not stick around for easy identification. You will see them if numbers merit action. The larvae of moths and butterflies or sawflies, slugs and snails are less mobile, but the damage can look quite similar. All of these creatures can chew holes and some can cut stems or skeletonize plants. Nocturnal munchers, like cutworms, slugs and snails can be discovered with a flashlight at night. Or you can place cardboard or moistened rolled newspaper under plants at night and shake them out into a pail in the morning for identification. Day feeders may be well camouflaged. Look for silk threads, frass (poop) and peek beneath leaves to discover who is doing the chomping.

If the leaves of your plant look like they were rubbed by sandpaper, this points to herbivores with rasping mouths like mites or thrips. They scrape off bits of surface tissue and suck the fluids out. The leaves can look speckled and brown from desiccation.

Sucking insects (like plant bugs, lace bugs, leafhoppers, spittlebugs, aphids, whiteflies, scale insects, mealybugs etc.) have mouth parts that can pierce leaves and stems to suck out plant fluids. Clues to these insects include curling, yellowing, distorted leaves or stunted shoots. Some also produce a sticky substance known as honeydew, which can attract ants. Mould can develop on the honeydew and may be the first noticeable symptom.

Plants can tolerate some defoliation and most damage in gardens is largely cosmetic. We must learn to take action only when pest numbers pose a threat to plant health or food production.
C. Kavassalis

Little trails or doodles inside of leaves or sometimes blotches are produced by leaf miners. These can be the larvae of flies or moths. As the name suggests these larvae drill through leaves feeding on the inside. Many are quite host specific …so knowing the name of the plant can quickly narrow the type of leaf-miner.
There are many more clues but this is a start. Help us help you, by looking for signs first. We can then try to provide you information to help you understand the role of the herbivore in your ecosystem and help you manage potential problems in an ecologically sustainable way.

Evidence of leaf miners: 1. Birch Leafminer, 2. Jewelweed Leafminer Fly 3. Spinach and Beet Leafminer

Plants can tolerate some defoliation and most damage in gardens is largely cosmetic. We must learn to take action only when pest numbers pose a threat to plant health or food production. Identifying what is consuming our plants is the first step in understanding the potential threat and developing a strategy to avoid serious damage or loss of crops.

We gardeners don’t like to hear this, but if nothing is eating our plants then something is very wrong in our gardens. Our plants are part of foodwebs. Herbivores, like caterpillars, eat plants and those herbivores are in turn food for various predators, like birds. No caterpillars – no birds – no butterflies. So accept some holes in leaves and expect some loss of flowers and fruits in your healthy garden that supports life.

Learn more:

Basic Entomology for Iden4fiers http://plantclinic.tamu.edu/…/TDAInspector-Training…Some Commonly Seen Damages

Seedlings chewed off at soil level: Cutworms.
Stems hollowed with larvae inside, leaves wilted or woody plants with trails under bark: Borers.
Roots or bulbs with signs of feeding or dead spots: Wireworms, many kinds of beetle grubs, weevils.
Fruits or plants spotted, sticky, slimy or frothy: Aphids, leafhoppers, spittlebugs, whiteflies, scales, and mealybugs.
Leaves with large ragged holes: Adult or larval stage of beetles, moth larvae.
Skeletonized leaves: Beetle larvae, pear slugs, thrips, and some caterpillar species.
Leaves curled, puckered or distorted: Aphids, leafhoppers, plant bugs.
General decline of a plant along with chewed roots: Root feeding larval stages of weevils, beetles or moths.
Dimples and/or distorted fruits and berries: Plant-feeding stink bugs called brown marmorated stink bug.
Trees and lumber with excavated cavities and frass (insect poop): Carpenter ants, termites.
Processed wood with small holes and fresh sawdust: Powderpost beetles.