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Garden Q&A: How to control a leafminer attack

Overnight, leafminers attacked my spinach and beets. I pulled my spinach and cut the leafminer-infested leaves off my beets. Are there other ways to organically control or prevent leafminers? Cutworms have been cutting off and carting away my seedlings, too! Would plant covers protect plants before they’re attacked?

When you spot the meandering tunnel of a leafminer eating between the upper and lower surface of a leaf, crush it with your fingers. This is your primary control method. This retains the leaves necessary, for instance, to build up the beets. Picked leaves should be discarded in the trash.

Spring tilling can kill overwintering pupae in the soil. Importantly, avoid pesticides, so beneficial parasitoid insects can start eating the leafminers. Cutworms are partially controlled by predator insects, like the six-spotted green tiger beetle pictured. Predaceous insects always lag a little behind their prey because they need prey around to eat in order to build up their populations. Search “leafminers vegetables” and “cutworms vegetables” on the HGIC website. And, yes, covering crops with row cover right after planting prevents feeding by many generations of both these pests.

We just had a tree taken down and the stump ground, leaving us with piles of shredded wood mixed with soil. Can we use this as mulch? Can we plant grass seed into this where the stump was?

Yes, you can use it as mulch, but not immediately. Freshly made mulch gives off gases that can damage leaves. If you have to spread it right away, keep it a few inches away from trunks and stems, as always, but also away from low leaves, for instance at the bottom of shrubs or perennials. Spread it thinly — it should never be more than 2- to 3-inches deep anyway. As fresh mulch begins to decompose, the process uses nitrogen in the soil that plants need. Apply some nitrogen fertilizer to compensate for this. Ideally, let your mulch/soil age for a season before spreading it. To plant grass seed on the stump site, remove the upper mulch/soil mix and replace it with topsoil. Mound the soil to allow for the settling and decomposition of the mulch/soil below.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Maryland’s Gardening Experts” to send questions and photos.

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About Mary Ellen Bellusci

Mary Ellen Bellusci is a longtime resident of Baltimore, Maryland... A foodie, traveler, writer, and pursuer of happiness.