What’s Eating My Leaf?

japanese beetle ted lare design & build

Sometimes it can seem like your garden is a battlefield where you have to constantly be on the lookout, waging war against all those pests that want to eat your plants. Here are six common garden pests that you will probably encounter in your Iowa garden. 

Japanese Beetle 

Japanese beetles are about half an inch long, and they have reddish-copper wings with a metallic green head. These pests are an invasive species and will eat the leaf, flowers, and fruit of plants. They also lay their larvae in the turf, which can cause browning (also known as grubs—and they are not conducive to a healthy lawn).

These pests chew holes in leaves, making them look like lace. If they’ve laid larvae in the turf, there will be spots that turn brown. Mostly they’re a cosmetic problem, but they can defoliate a plant to the point of death during years of heavy beetle population numbers.

In late June or Early July, knock the beetles off your plants into a bucket of soapy water. Check the tops and bottoms of leaves. A neem solution can be a deterrent if you don’t have a large infestation. It’s not a great idea to use insecticide since it will also kill other essential insects. 

potato beetle ted lare design & build

Potato Beetle 

Colorado potato beetles are about ⅓ of an inch long. They have a round, hard shell with a cream background with brown stripes down the back, and spots on their head. 

Potato beetles can do damage to potatoes, tomatoes, eggplants, peppers, and tobacco plants. These pests will turn the foliage of your plants into skeletons, eating all the soft tissue between the leaf ribs. 

Potato beetles may be around all growing season, so keep your eyes open—row covers for potatoes and crop rotation help. Products like BT (Bacillus thuringiensis) and neem oil also work well. Handpick them as you see them, crushing them or dropping them into soapy water.


Hornworms are a caterpillar that is usually shades of yellow to white. They have horns on the last segment of their body, and will have white marks down their sides. 

These pests defoliate plants, usually starting at the top; as they get bigger, they get faster, and can devour an entire plant. 

Handpick and drop them into soapy water; they camouflage well. You can till the soil late in the fall to disturb any burrowing for winter. If you find hornworms that have many projections from their body, leave them be. They’ve been parasitized by braconid wasps which will help kill more of them.

corn earworm ted lare design & build

Corn Earworms 

​​The adults are dark brown or green moths. The larvae are the real pest, though, and they are about 1.5 inches long, pink, green, or yellow, with cream, yellow, or black stripes down the whole body. 

These pests feed on the leaves, shoots, tassels, and ears of the corn.

Corn earworms appear in June. As soon as the silks develop on your corn, clip a clothespin at the top of the ear to prevent the larvae from entering. You can release Trichogramma wasps to parasitize them. BT can be combined with corn oil and applied to the tip of each ear. 

Spider Mites 

These teeny-tiny pests are hard to spot, but they leave a fine webbing that you usually notice first. They are usually red; if you shake an infested plant over a piece of paper, you may see a bunch of tiny red dots. 

Spider mites feast on the most tender parts of lush plants. Foliage will have a speckled appearance, and the entire leaf may turn yellow and die. The webbing will be in the nooks and crannies of stems and leaves. 

They’re mostly problematic when the weather is hot and dry. Encourage beneficial insects in your gardens like ladybugs and beneficial nematodes. You can spray them off with water, treat them with neem oil or insecticidal soap.

aphids on stem ted lare design & build


Aphids are tiny little pear-shaped pests that can be green, yellow, brown, red, black, or gray. Some fly, and some don’t.

They attack all sorts of plants, particularly younger, lush growth. Similar to spider mites, they suck the plant’s sap out from the underside of the leaves. Leaves will twist, curl, and turn yellow. There may be spots of droplets of honeydew on the leaves below where the aphids are. 

Make your garden welcoming for ladybugs. If you start plants from seed, watch them. You can spray the aphids off your seedlings with a spray bottle. Older and stronger plants can take a stronger spray from the hose. You’ll need to repeat the treatment 2-3 times a week until they’re gone.

Figure Out What’s Eating that Leaf ASAP!

Early identification and treatment of these pests is key to keeping your plants safe and growing well. If you’re seeing signs of a pest chowing down on a leaf, you can bring pictures of the damage and the pest to the garden center (in a tightly sealed bag) or submit samples to the ISU extension Plant and Insect Diagnostic Clinic. There are specific guidelines for how to submit samples.


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