| | Causal Agent: Chrysanthemum leafminer – Liriomyza trifolii; vegetable leafminer – Liriomyza sativae; pea leafminer – Liriomyza huidobrensis; birch leafminer – Fenusa pusilla, Profenusa thomsoni; aspen serpentine leafminer – Phyllocnistic populiella; Phyllonorycter nr. salicifoliella and P. nr. nipigon; lilac leafminer – Gracillaria syringella; cottonwood leafmining beetle – Zeugophora acutellaris, Z. abnormis; European alder leafminer – Fenusa dohrnii; plus other species
Crops Affected:
Edible crops – beets, spinach, Swiss chard, tomato, cole crops, cucurbits, peas, beans, lettuce, etc.
Ornamental crops - aster, begonia, dahlia, impatiens, lily, marigold, petunia, and verbena, greenhouse ornamental crops (e.g. chrysanthemum, gerbera), woody ornamental trees and shrubs (e.g. birch, poplar, aspen, oak, willow, alder, lilac, etc.)
Life Cycle:
- Adult insects are flies, moths or beetles which lay their eggs on/in the undersides of host leaves (depending on the species)
- Larvae tunnel into the leaves to feed between the upper and lower leaf surfaces (epidermal layers), forming “mines”
- Larvae develop fairly rapidly, depending on the species and the temperature
- Larvae typically complete development by exiting the leaf and dropping to the soil to pupate
- Damage is largely cosmetic
- Yields of edible plants are typically not affected unless severe defoliation occurs
- Damage is typically insufficient in ornamental species to cause lasting harm to large woody plants
- Populations can increase rapidly, particularly in protected environments, depending on the species
- For woody ornamental hosts, flies emerge in spring and often lay eggs as leaves are starting to emerge from buds
- The presence of the various pest species will vary by region, with some being more prevalent in some areas and others not being present at all
Symptoms:
- Mines are visible, twisting back and forth across the leaves of host plants
- In some host species, mines become pockets of spaces, within which larvae can be observed feeding
- Some mines resemble blotches
- Differences between the appearance of mines can be indicative of the pest species
- Leaves may appear brown and dried out, as the leaf tissues die off as mines are enlarged
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Leafmining damage on birch & cutleaf weeping birch – note: visible larvae | Leafmining damage on spinach leaves |
Photos by Robert Spencer | Photo Courtesy: Whitney Cranshaw, Colorado State University, Bugwood.org |
Monitoring:
- In greenhouses, yellow sticky traps can be used to monitor adult fly populations
- Watch fields for signs of early mining and be prepared for preventative protection in advance or
to stop later generations from developing
Management:
- Ensure that plants have adequate water and nutrition to produce strong, healthy growth
- Rotate to non-host crops on a regular basis
- Covering edible crops can restrict access to the plants by adults
- Resistant or tolerant varieties can be available for some host crops
- Control weeds, to prevent population carryover between crops
- Early removal of mined leaves can interrupt the life cycle of the pests
- Parasitic wasps can be effective biological controls some species, particularly in protected crops (e.g. greenhouse)
- The use of registered insecticides can be used to control adult leafminers
- Resistance can develop quickly in this pest – use caution and rotate chemical groups
- Control options may be limited in some crops
- It is very difficult to control leafminers in woody ornamentals, other than through the use of systemic insecticides applied early in the spring
- There are very few options available in the present day
- Strict sanitation programs (in protected environments) can help to keep populations in check
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