Leaf miner is a common term used to describe various species of insects that feed on the tissue inside plant leaves, leaving visible trails or tunnels known as “mines.” Among them, the spinach leafminers are early-season pests that attack crops and weeds in the plant family Chenopodiaceae, which includes popular vegetables like chard, beets, and spinach.
These pests are small flies that lay eggs on the surface of leaves, and the larvae that hatch burrow inside the leaf tissue to feed and grow. While leaf miners may not directly kill plants, their damage can reduce yields and quality of crops, and severe infestations can lead to premature leaf drop and weaken the plant’s overall health.
Management of Leaf Miner in Spinach
The life cycle of Leaf Miner
The life cycle of the spinach leafminer begins with adult flies laying oblong white eggs in neat clusters on the underside of leaves. The eggs are less than 1 mm long and hatch in 3-6 days. The larvae which emerge from the eggs, known as maggots, burrow into the leaf tissue to feed and grow. The larvae may migrate from leaf to leaf down a row, causing damage to multiple plants. The larvae grow fully and drop into the soil to pupate in just a few weeks. However, they may also pupate inside the leaf.
The pupal stage lasts 10-12 days, after which adult flies emerge, and the cycle begins again. The entire life cycle of the spinach and beet leafminer takes 30-40 days. There are three to four generations of leafminer per season. These generations overlap, causing continuous season-long damage to succession-planted crops such as spinach, beets, and chard. Mid-late May, late June, and mid-August are peak activity periods for leafminer. After August, pupae enter the overwintering phase and won’t emerge until spring, when the cycle starts anew.
Identification of Leaf Miner in Spinach Field
- Adult: Small fly less than 2 mm (0.08 in) in length with a wing length equal to or slightly longer than the body. Flies have yellow heads and grayish-to-black bodies with yellow markings on their underside. Wings are dark in color and are folded horizontally over the back when at rest.
- Egg: White or yellowish, oval, and 0.2-1.0 mm (0.01-0.04) in length.
- Larva: Legless maggot that can be transparent immediately after hatching, changing to white or cream, and yellowing with age. The body is oval or wedge-shaped, 2-3 mm (0.08-0.12 in) in length, with typically dark-colored mouthparts. Two spiracles (breathing tubes) are present at the posterior end.
- Pupa: The pupa is enclosed within the last larval exoskeleton forming a smooth puparium. Color ranges from golden or reddish to dark brown, and length ranges from 1.5-3.5 mm (0.06-0.14 in). Two spiracles (breathing tubes) are visible on the posterior end.
Damage Symptoms of Leaf Miner in Spinach Field
- Punctures from feeding and egg-laying appear as white stipples primarily on the upper surface of the leaf
- Punctures can allow bacterial and fungal diseases to enter the plant
- The larva causes major damage to the plant as it feeds and tunnels through the leaf’s mesophyll layer
- Resulting damage includes blisters, blotchy mines, or serpentine tunneling
- Frass (feces) may be visible within mines and can contaminate leaves intended for human consumption
- Heavy feeding damage can reduce photosynthesis, causing leaves to dry and drop
- Serious infestations usually occur late in the season and can affect large areas of the leaf
- In warm areas and greenhouse production, damage may be more severe.