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Ministry of Agriculture, Food and Rural Affairs

Leafminers

Leafminer adult Leafminer cucumber leaf damage Leafminer beet damage
Click to enlarge.

Beginner

Scientific Name
Liriomyza spp.

Identification

  • Adult leafminers are small (2- 3 mm, 1/12- 1/8 in.), shiny black and yellow flies
  • Eggs are laid in the leaves, leaving small bronzed puncture marks 
  • Females pierce the leaves to feed on plant sap 
    Larvae tunnel within the leaf tissue forming the characteristic mines
  • Depending on the species mines can be serpentine or straight
    The larvae of leafminers are small, pale yellow maggots

Often Confused With
Herbicide injury
Leaf scald

Virus damage

Period of Activity
Optimal temperatures for feeding and egg laying range between 21°C and 32°C (70- 90°F). Egg-laying is reduced at temperatures below 10°C (50°F).

Scouting Notes
Watch carefully for the presence of adult leafminer flies and mined leaves; make careful note of problem areas. Yellow sticky traps are excellent for monitoring adult flies.

Thresholds
None established. Control decisions should be based on the extent of the infestation and the effect of damage on marketability.

Advanced

Scientific Name
Liriomyza spp.

There are 4 main species of leafminers which may attack vegetables and ornamentals in North America. Identification of the species may be difficult since they are very similar in appearance and behaviour. Leafminers are flies in the order of insects called Diptera. The 4 main species are Liriomyza trifolii (Burgess) (unofficial 'serpentine' leafminer), Liriomyza brassicae Riley (official 'serpentine' leafminer), Liriomyza sativae Blanchard (vegetable leafminer) and Liriomyza huidobrensis (Blanchard) (pea leaf miner).

Identification
Leafminers are small (2 - 3 mm or 1/12- 1/8 in.), shiny black and yellow flies which lay their eggs into leaves so that the larvae feed between the leaf surfaces. Feeding punctures and egg-laying punctures may also cause serious damage in some cases. Larvae tunnel within the leaf tissue forming the characteristic mines. Depending on the species mines can be serpentine or straight. The larvae of leafminers are small, pale yellow maggots.

Often Confused With
Herbicide injury
Leaf scald

Virus damage

Biology
All of the leafminer species have a similar development. However the pea leafminer takes slightly longer. The eggs are laid in the leaves, leaving small, bronzed puncture marks called 'stipples'. After 2- 3 days of incubation, the eggs hatch.

Larvae tunnel within the leaf tissue forming the characteristic mines, then cut a semi-circular opening in the tissue and drop to the soil to pupate. If temperatures are warm, larvae can reach maturity in 4- 6 days and the pupal stage lasts another 4- 7 days during the summer.

Pupae can survive for up to 90 days when temperatures are cool or host plants are not available. The life cycle could be as short as 14 days at 30°C (86°F) or as long as 64 days at 14°C (57°F). Mating, egg-laying, larval emergence from leaves and adult emergence from pupae tends to occur mostly in the morning, depending on temperature and cloud cover.

Period of Activity
Optimal temperatures for feeding and egg laying range between 21°C (70°F) and 32°C (90°F). Egg-laying is reduced at temperatures below 10°C (50°F).

Scouting Notes
Watch carefully for the presence of adult leafminer flies and mined leaves; make careful note of problem areas. Yellow sticky traps are excellent for monitoring adult flies.

Leafminer feeding reduces the plant’s photosynthetic capacity. The mines also affect marketability and provide an entrance for disease organisms.

Thresholds
None established. Control decisions should be based on the extent of the infestation and the effect of damage on marketability.

Management Notes

  • Begin cleanup immediately following harvest and dispose of debris as far as possible from the growing area. Totally cover or bury debris to reduce the dispersal of any emerging leafminer flies.
  • Degrees of infestation vary with the type of crop, neighbouring crops, weeds, temperatures and leafminer species.
  • Crop rotation is an effective pest management tool. Alternating leafminer susceptible crops with leafminer resistant crops reduces the population.
  • Many wild plants act as hosts for leafminers. Maintaining weed free conditions both in the greenhouse and the field is recommended.
  • Few pesticides are labelled for control of leafminers in Canada. Leafminers are known to develop resistance to insecticides quite quickly. When available, always rotate between insecticide groups. Most effective control is obtained with systemic or translaminar products which target the larvae. Thorough coverage of the crop is essential for effective leafminer control.
  • Time insecticides to have the most impact on susceptible stages. Based upon what is known already, sprays applied early in the morning should be most effective. Spraying should only be based upon regular and consistent scouting information.