Adult is a small black and yellow fly (seldom seen). The adult fly lays eggs on underside of leaves; tiny yellowish larvae (1/8" long) hatch and tunnel inside leaves. Several generations develop each summer. It is the most destructive pest of spinach; also infests red beets. Tunnels cause whitish dead areas; plant growth may be stunted.
Spray beet tops and spinach with spinosad. Ensure coverage on the underside of leaves. We recommend Bull's-Eye Bioinsecticide. Super- Light Insect Barriers also provide a highly effective defense against leafminers on both spinach and beets.