Description of the Pest
Adult leafminers are small (1.8 mm), yellow and black flies that are about the same size and shape as fruit flies. In contrast to shore flies, leafminer adults are brightly colored and have clear wings. They are often found on yellow flowers or objects. Females insert their eggs within leaves and also puncture the leaf surface with the ovipositor to feed on damaged plant tissue. Larvae have three instars, forming larger mines inside the leaves as they grow. Liriomyza trifolii mines are readily observed from the top of the leaf, while Liriomyza huidobrensis mines may only be visible from the underside of the leaf. Liriomyza huidobrensis mines tend to follow the veining pattern of the leaf. After completing their feeding, larvae drop from leaves to pupate in the soil. Liriomyza trifolii can complete one generation in 14 days at 95°F, 64 days at 59°F.
When populations are high, stippling, caused by females puncturing the leaves with their ovipositor to feed and lay eggs, can be serious. However, most of the damage is caused by the larval mines that detract from the aesthetic value of the crop.
Biological control normally keeps these species in check in outdoor situations. Outbreaks of leafminers frequently occur following the disruption of their parasites with broad-spectrum insecticides. For this reason, try to use selective insecticides through the entire production cycle so that parasites can be conserved. The parasites Diglyphus spp. and Dacnusa sibirica are commercially available to control leafminers and may be useful in greenhouse situations, especially if greenhouses are screened to exclude adult leafminer movement into greenhouses. For more information, see BIOLOGICAL CONTROL.
Because leafminers feed on a large variety of plant species, keep production areas free of weeds, which can serve as reservoirs for leafminer populations. Leafminers breed in weed or crop hosts outside of greenhouses, so weed management outside the greenhouse and exclusion of immigrating adults are especially valuable as management practices. Effective screens require a pore width of 600 microns or smaller. Carefully inspect plants being brought in to start a new crop to ensure that they are free of mines; discard infested plants or leaves. Steam planting beds immediately after removing infested plantings to eliminate leafminer pupae in the soil.
Monitoring and Treatment Decisions
Yellow sticky cards placed in greenhouses will capture adults. Place one trap per 10,000 sq. feet and monitor weekly. For more information, see MONITORING WITH STICKY TRAPS and ESTABLISHING ACTION THRESHOLDS.
Insecticide resistance is so widespread that the effectiveness of each material depends on the tolerance of each treated population. Rotation to a new class of insecticides every 1 to 2 months is advised.
Selected Materials Registered for Use on Greenhouse or Nursery Ornamentals
Read and follow the instructions on the label before using any pesticide. Before using a pesticide for the first time or on a new crop or cultivar, treat a few plants and check for phytotoxicity. Also consider pesticide resistance management and environmental impact.
|Manufacturer||REI1||Mode of action2||Comments|
|insect growth regulator||A.||azadirachtin
|OHP||4||un||Must contact insect. Repeat applications as necessary. Label permits low-volume application.|
|SePRO||12||un||Do not exceed 22.5 oz/acre/application.|
(Citation 75 WP)
|Syngenta||12||17||Certification training required to use this product. Also effective against fungus gnat larvae. Labeled for low volume applications.|
|Chemtura||12||15||Use no more than twice per year and don't exceed 52 oz/acre/year. Don't use on poinsettia.|
|Valent||12||7C||Do not apply more than 2 times per cropping cycle or per 6 months.|
|Syngenta||12||6||Label permits low-volume application.|
|Cleary||12||4A||Apply as a foliar spray.
|Valent||12||4A||Can be applied as a drench or foliar spray.|
|OHP||12||4A||Not to be used more than once every 16 weeks. Do not apply to soils that are water logged or saturated. Do not apply to bedding plants intended to be used as food crops.|
|(Marathon 60 WP)||As above. Apply only as a drench.|
|Syngenta||12||4A||Can be applied as a drench or foliar spray.|
(Orthene T, T&O Spray3)
|Valent||24||1B||A number of chrysanthemum varieties have exhibited phytotoxic reactions. In greenhouse only labeled for use on anthurium, cacti, carnation, rose, orchids, some foliage plants, young poinsettia and some varieties of chrysanthemum. Can stunt new growth in roses.|
|24||1B||An aerosol for greenhouse use only.|
|FMC||12||3||Direct application to blooms may cause browning of petals. Marginal leaf burn may occur on salvia, diffenbachia, and pteris fern. Label permits low-volume application. Do not apply more than 2 lb a.i./acre/year.|
||12||13||Greenhouse use only. Do not exceed 3 applications/growing cycle.|
|4||5||Do not apply more than 10 times in a 12-month period. Compatible with most beneficials, but highly toxic to bees and hymenopteran parasites. Direct contact can cause significant mortality to Phytoseiulus persimilis.|
|1||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.|
|2||Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|3||This material is effective, but not specifically labeled for this pest.|
|*||Restricted use pesticide. Permit required for purchase or use.|