MG Volunteer: “OSU Extension Master Gardener volunteer. How may I help you?”

Caller: I have damage on my spinach leaves. What is infecting my spinach, and what do I do to get rid of it? It is May now, and some of the leaves have curly looking, whitish, or silver-looking tracks meandering on the leaves and then it turns into a white big blotch
MGV: How many spinach plants do you have and how many of them are infected?
Caller: I have two rows of spinach, and I would say that about one quarter to one third is infected.
MGV: When did you first notice the damage?
Caller: Some of the plants seemed to be effected as seedlings, and now more and more plants are infected as time goes by.
MGV: Have you seen any insects on your spinach plants?
Caller: Just some small fly looking things. They don't appear to be eating anything, just landing on the plants. The white areas don't have any holes that I can see.
MGV: Have you gone out to look at night?
Caller: No.

Diagnosis:

Spinach Leaf Miner: Adult lays eggs on underside of leaves. Larvae burrow in between the cell layers of the leaf creating serpentine tracks in the leaf. Maggots emerge from the leaves and drop down into the soil to form pupa, the pupa then turn into flies allowing several generations to grow per year. To read more about this, visit this website.

Recommendations:

Cultural: To prevent infections, cover seedlings with row cover if not yet infected. Check underside of leaves regularly and squash egg masses. Pick off and destroy infected leaves. Also check plants NOT infected for eggs. Cultivate frequently around plants. Rotate crops. Remove plants that are hosts to leaf miners (pigweed, plantain, chickweed, lamb’s quarter).

Biological: Natural predators such as parasitic wasps and entomopathogenic nematodes. Create plantings to attract parasitic wasps.

Chemical: Not recommended as control of adult stage as it also harms beneficial insects and could result in higher numbers of the pests. Chemical control of larvae not effective; larvae are protected by the leaf cells they are eating.

(Thanks to the Benton County Master Gardeners for developing this scenario)