Leaf miner on Spinach

Q: Every year my spinach gets leaf miner making the leaves inedible. How do I get miner free spinach?

A: I feel your pain. I hate leaf miner. Leaf miners are one of the most frustrating pests on spinach because they live inside the leaf, where sprays can’t reach them. The adult flies lay eggs on the underside of the leaves.  When the larvae hatch out, they tunnel into the leaves making them look very unappetizing. Plus, the eggs stuck to the underside of the leaves are gross.

One of the most reliable methods to prevent leaf miner in spinach is by using floating row covers. It’s important to know that leaf miners overwinter in the soil where spinach, beets or chard grew the previous year. If you plant those crops in the same place and cover with a floating row cover, you are essentially trapping emerging leaf miner adult flies underneath the cover with your precious plants.  If you intend to use this method of prevention, be sure to plant your new crop in a part of the garden well away from where you grew spinach, chard or beets the previous year or it’s a waste of time and money.

If floating row covers sound like too much trouble (I agree), simply remove infested leaves as you see them and place them in a covered trash can. NOT in the compost pile where they can finish maturing into new flies.  Cut off the infested portion of the leaves and the miner free portions are fine to eat.

Some studies show that planting flowers like dill, alyssum, and fennel nearby helps attract natural predators like parasitic wasps (Diglyphus isaea) to the area. Helping to control the pest naturally.

 Organic sprays like Spinosad (very effective) or Neem oil (moderately effective) must be applied to new larvae which hatch out on the underside of the leaves. Have fun with that. Larvae already in the leaves will not be effected by sprays. Spray in the evening to protect beneficial insects. NEVER use a systemic on edible crops.

Rotate Crops. Leaf miners overwinter in soil. Avoid planting spinach or related crops in the same spot each season. Rotate with unrelated vegetables for a year. If that’s not possible, rough up the top 2-3” of soil in late fall to expose overwintering pupae to the elements and predators.

Garden Wise Guy tip:  Spinach leaf miners are small flies, and most of their activity happens very close to the ground.  They tend to move short distances horizontally rather than flying high or far.  So I like to plant spinach in 12” hanging baskets at least 6-10’ above the ground.  My deck is above a walkout basement so I can easily hang baskets 10 or more feet above the ground and still be accessible.  And chard, another leaf miner favorite, looks great mixed with annuals up high on my deck.  Nearly 100% miner proof as long as I use fresh potting soil each year.  Once it gets hot and spinach bolts (goes to seed) the baskets can be refilled with decorative plants for the rest of the season.

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Read our Q & As with Keith Funk answering common Colorado gardening questions here. See his website: gardenwiseguy.com and hear him on the Garden Wise Radio Show.