Insect of the Month - Leafminers

  Hort Snacks - July 2018
Download 505K pdf file ("HortSnacks-July2018.pdf")PDF
     Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
     Hort Snacks HomeHort Snacks Home
 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
  • 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
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,

  • 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
  • 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
Share via
For more information about the content of this document, contact Robert Spencer.
This information published to the web on June 26, 2018.