Vegetable Program
Insect Management

Leafminer, Beet and Spinach

Spinach Leafminer Injury

It’s disappointing to discover that your high-value early spinach and chard leaves are showing ugly feeding mines just as they are ready for harvest. Spinach leaf miner, typically an early-season pest, may cause damage to early greens. It attacks crops and weeds in the plant family  Chenopodiaceae which includes the crops chard, beets, spinach as well as weeds like lamb’s quarters and pigweed . Leafminer is a fly larva that burrows between the layers of a leaf eating everything but the epidermis. Early damage is a slender, winding ‘mine,’ a tunnel, but later these expand and become blotches on the leaves. Inside the mine is a pale, white maggot. Spinach leafminer( Pegomya hyoscyami Panzer) and beet leafminer (Pegomya betae) are very similar species in behavior, appearance, plant hosts, and damage and generally cannot be distinguished in the field.

The fly overwinters as pupae in the soil and hatches in late April and May. The adult fly then lays eggs on the leaves and the resulting larvae begin their damage. The oblong white eggs, less than 1 mm long, are laid in neat clusters on the underside of the leaves. They are easy to spot if you scout by looking under the leaves.  The maggots may migrate from leaf to leaf down a row.  They become fully grown in just a few weeks and drop into the soil to pupate. The entire life cycle is 30-40 days. There are three to four generations per season.  Typically mid-late May, late June and mid August are peak activity periods.

In most seasons the damage is minimal and the plants will out grow it leaving only early leaves with cosmetic damage.  In other years, or other fields in the same year, the damage may be great and if the plants are hit early and growth is slow because of weather conditions, the loss may be great.  Treat when eggs or first tiny mines are noticed. See the New England Vegetable Management Guide for products; there are both conventional and organic product available. An adjuvant is recommended to improve efficacy.

Weed control and crop rotation are the first line of defense. Row covers can also be used to exclude flies if placed over the crop before flies are active. 

-R. Hazzard. Sources Eric Sidemann, Maine Organic Farmers and Gardeners Association; J. Capinera, Handbook of Vegetable Pests.

Updated May 2009