If your plant leaves look like someone was doodling squiggly lines, you have leaf miners. Leafminers are the larvae of various beetles, flies, moths and sawflies. The adult lays their eggs on the leaf and the larvae burrow into the leaf and tunnel through it, feeding and leaving a transparent trail of where they've been. If you look closely, you can often see a dark dot at the end of one of the lines. That's the culprit at work.
Not all leafminers zig zag their way through leaves. If you see a similar whitish transparent blotch, this could also be a leaf miner. Blotchy leafminer damage is often mistaken for some type of disease. The photo here is an okra leaf, but many plants are attacked by leafminers. Columbine is almost guaranteed to have a few. The damage is rarely severe enough to kill the plant, but it is unsightly. And in the case of vegetables grown for their leaves, like spinach, chard and beet greens, leafminers can mean a loss of a crop.
Controlling Leafminers
- Least Toxic: Insecticides are rarely recommend to control leafminers. Since the damage is mostly cosmetic, the remedy is to remove the affected leaves. This does more than improve the appearance of the plant. It also gets rid of the existing leafminers before they become adults and lay more eggs.
- Less Toxic: If you know that a certain plant is susceptible to leafminer every year, you can target the adults before they lay their eggs, by spraying early in the spring with an insecticide such as neem.
- Last Resort: There are some systemic Insecticides that are labeled for use on leafminers. Insecticides containing acephate (Orthene) or imidacloprid can be effective if used before damage is severe. No systemics are currently available for non-commercial use on edible plants.
