If the leaves on your shrubs, flowers or vegetables have pale, winding lines or puffy brown blotches, you're looking at the work of leafminers. Around your Short Hills home, they can show up on boxwood, holly, columbine, birch, spinach, chard and many other plants. The trails look alarming, but in most cases the damage is more about looks than plant health. Below, we'll cover what leafminers are, how to recognize the different kinds of mines, when they're actually a problem and what you can do. If you're not sure what's damaging your plants, our pest inspection services can help you identify it.
What Leafminers Are
"Leafminer" isn't one insect. It's a way of feeding. The larvae of certain small flies, moths, beetles and sawflies live inside a leaf, eating the soft tissue between the top and bottom surfaces. The leaf's outer skin stays intact, so the larva is protected while it feeds.
The adults are usually small and easy to miss. Many are tiny flies or moths. Females lay eggs on or in the leaf, and the larvae hatch and tunnel in. When they finish feeding, some leave the leaf to pupate in the soil, while others stay inside until they emerge as adults.
Types Of Mines You May See
- Serpentine mines. Thin, winding trails that get wider as the larva grows. Columbine and many vegetables show this pattern.
- Blotch mines. Irregular blister-like patches where the larva fed in one area. Spinach, chard, beets and birch often show blotches.
- Swollen or puckered leaves. On boxwood, mines often look like small blisters on the underside of the leaf, with orange larvae inside.
- Trails with dark lines. Many mines have a thin dark line of waste running down the middle.
Holding a mined leaf up to the light often shows the larva or its waste inside. That's a quick way to tell a mine from a disease spot. Disease spots usually look the same from both sides of the leaf and don't have a clear tunnel or a path that widens as it goes. A mine with a small exit hole or an empty, dried-out look usually means the larva has already left.
Common Leafminers In Home Landscapes
- Boxwood leafminer. A small fly whose larvae feed inside boxwood leaves, causing blistering and yellowing.
- Holly leafminer. Leaves on holly show winding or blotchy yellow trails.
- Columbine leafminer. Pale, squiggly lines across columbine leaves.
- Vegetable leafminers. Blotches on spinach, beets and chard that make leafy greens less appealing to eat.
- Birch leafminer. A sawfly whose larvae make brown blotches in birch leaves.
Are Leafminers A Problem?
For people, pets and your home, no. Leafminers don't bite, sting or come indoors. They don't damage wood, fabric or food in your house.
For plants, it depends. On most trees, shrubs and perennials, a few mines are cosmetic. The plant still has plenty of healthy leaf area. Problems come when mining is heavy year after year:
- Boxwood with many mined leaves can look thin and yellow and may drop leaves early.
- Heavily mined leafy greens can become unusable even if the plant survives.
- Young or stressed plants have less to spare, so repeat damage can slow their growth.
Leafminer damage is sometimes confused with stippling from lace bugs or mites. Those insects feed on the outside of the leaf, not inside it. If you're comparing sap-feeding insects on your shrubs, our guide on aphids vs. scale insects is a good starting point.
What You Can Do
- Pick off mined leaves. On small plants and vegetables, remove leaves with active mines and throw them in the trash, not the compost.
- Clean up fallen leaves. Rake and dispose of fallen leaves from affected plants, since some leafminers finish their life cycle in leaf litter or soil.
- Use row covers on vegetables. Lightweight fabric keeps egg-laying adults off spinach, chard and beets.
- Keep plants healthy. Water during dry spells and avoid overfeeding with fertilizer, which pushes out the tender growth many leafminers prefer.
- Choose resistant plants. When replacing boxwood or holly, ask a nursery about varieties that are less prone to leafminers.
- Be patient with sprays. Because larvae are protected inside the leaf, many sprays don't reach them. Timing matters, and an arborist or your county office of Rutgers Cooperative Extension can advise for your specific plant.
When To Call A Professional
If a prized shrub or tree is losing leaves every year, a certified arborist can assess its health and recommend treatment. EcoFusion doesn't treat trees or garden plants. Where we help is identification and anything that's moving from the yard into your home. Our NJ DEP-licensed technicians can inspect your property, figure out what's causing the damage you're seeing and recommend a plan using Integrated Pest Management and EPA-registered, eco-safe products.
Leafminers leave odd-looking marks, but they're rarely a serious threat on their own. With a little cleanup and attention, the shrubs, flowers and vegetables around your Short Hills home can stay healthy and green.