By Gregg Nuessly

Scout your seedlings twice weekly to protect them from the serpentine leafminer. Left unnoticed, high populations of leafminer can kill or stunt young plants.

What to look for

Adult serpentine leafminers are small, black flies with yellow markings. They deposit their eggs into leaves. Larvae emerge within four days to feed on the leaves. The yellow larvae grow to about 1/8 inch long and complete development in 10 to 14 days. Full-grown larvae then cut themselves out of the leaves and travel to the soil or leaf trash to pupate and complete their metamorphosis to adulthood.  

Serpentine leafminers are fly pests of leafy and fruiting vegetables and floricultural plants. Adult females puncture holes in leaves for feeding and egg-laying that result in raised, discolored scars. Leafminer feeding produces white- to green-colored tunnels on the leaves. Leafmining reduces photosynthesis and food availability to the growing plant.

Insecticide use can be justified when an average of more than one mine per plant is found in young leafy vegetables. Protection of wrapper leaves may require more frequent scouting and treatments.

Disk fields to destroy and cover infested crop residues as soon as possible after harvest to reduce infestation of neighboring fields by emerging adults.

Mining damage

Older plants more readily tolerate attacks by this pest. But mining on lettuce and cabbage wrapper leaves, and leaves of flowering broccoli stalks can throw the heads out of grade — even though the damage often is merely cosmetic. High levels of damage result in defoliation of fruiting vegetables.

Rotate to prevent resistance

The use of broad spectrum insecticides can eliminate natural enemies and result in leafminer outbreaks.

The serpentine leafminer developed resistance to most insecticides labeled for its control prior to 1990. Cyromazine and abamectin were labeled for its effective control during the 1990s. Leafminer resistance to these materials, as well as to similar products containing spinosad, has now developed to levels of concern in several U.S. greenhouse facilities.

It is important for growers to continue to strictly rotate these valuable insecticides according to their labels in order to manage resistance development and preserve their efficacy. Concerns about insecticide efficacy should promptly be reported for further evaluation.

Gregg Nuessly is an associate professor at the University of Florida Institute of Food and Agricultural Sciences Everglades Research and Education Center, Belle Glade, (561) 993-1559. E-mail is

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