Biology and Management of Liriomyza Leafminers in Greenhouse Ornamental Crops - Department of Entomology at Texas A&M University - Extension Publications
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November 2005

Biology and Management of Liriomyza Leafminers in Greenhouse Ornamental Crops

Carlos E. Bográn, PhD. Texas A&M University. 2150 TAMU, College Station, TX 77843-2150

Leafminers are insects that develop inside the leaves of their host plants. There are several groups of leafminer species but Liriomyza leaf-miner flies (Diptera: Agromizidae) are the most important group in ornamental crop production. Key pest species in ornamentals include the American serpentine leafminer (L. trifolii) and the pea leafminer (L. huidobrensis). Historically, leafminers have presented serious control challenges for growers as populations are capable of developing resistance to common insecticides.

Identification. Adult Liriomyza are between 1/16 and 1/8 of an inch (1-3 mm) in length, yellow and black in color and have one pair of clear wings (Figure 1). Larvae (maggots) are light yellow in color and cylindrical in shape but are not easily observed because they occur inside the leaf tissues. Pupae are oblong in shape and brown in color. It is difficult to distinguish among Liriomyza species but in general, the adult L. trifolii is smaller and relatively more yellow in color than L. huidobrensis. Leafmines are produced by the larvae of both species, but their shape and position on the leaf may also provide clues to species identification. Liriomyza trifolii leaf-mines are more commonly found on the upper leaf surface whereas L. huidobrensis mines mostly occur on the lower leaf surface. Liriomyza trifolii leaf-mines are also narrower and may occur near the leaf margin whereas L. huidobrensis mines are more frequently found near the base of the leaf, often along the middle veins.

Figure 1. Adult Liriomyza spp . Photo credit: Clemson University - USDA Cooperative Extension Slide Series, www.forestryimages.org

Biology and Damage. Adult females feed on leaf tissues by puncturing the leaf surface with their ovipositors and ingesting the liquid cell contents. Females also puncture leaf tissue to lay their eggs and may live for 7 to 10 days. Both feeding and oviposition punctures turn white and damaged foliage looks stippled or speckled. Eggs hatch 2-5 days after oviposition. Each larvae feeds on leaf tissue making a winding tunnel (serpentine leaf-mine) or blotch on the leaf. The leaf-mines become increasingly larger in size as the larvae feed and grow through 3 immature stages (instars). Once feeding is completed, mature larvae cut a slit in the leaf surface, exit the leaf and drop to the ground (or potted soil-mix) where they pupate. Many generations can occur each year as long as temperatures are above 50 °F (10 °C). Egg to adult development may take as little as two weeks at 95 °F (35 °C) or as long as 8 weeks at 60 °F (16 °C). Liriomyza huidobrensis grows best under moderate temperatures (at or bellow 70 °F) while L. trifolii prefers warmer summer temperatures (above 75 °F). Most damage is caused by the larvae. Mined leaves are unattractive and unmarketable (Figure 2). Some damage may be tolerated in crops where foliage is not marketed, such as cut flower and seed production crops. Heavy damage may slow plant growth and cause defoliation.

Figure 2.Liriomyza spp. feeding damage. Photo credit: Alton N. Sparks, Jr., The University of Georgia, www.forestryimages.org

Host Plants. Liriomyza leafminers can attack a large variety of plant species including crops and weeds. Some of the most common ornamental hosts include: Chrysanthemum and Dendranthema (chrysanthemums), Gypsophila (baby's breath), Dianthus (carnation); Petunia, Tagetes (marigold) and Viola . Many food crop species such as bean, beet, carrot, celery, cucumber, eggplant, lettuce, melon, onion, pea, pepper, potato, squash, and tomato are also leafminer hosts.

Integrated Pest Management. The objective of leafminer management should be to avoid plant damage (high densities of large mines) by integrating cultural practices and control alternatives into an Integrated Pest Management (IPM) program. Successful leafminer IPM involves: minimizing adult movement into the greenhouse, quick and accurate diagnosis to select proper management action, frequent monitoring of populations during conducive periods and using monitoring data to select and time any necessary treatments.

Under certain temperature, humidity, water and shade conditions, pesticides may cause injury to certain plants (phytotoxicity). Generally, apply pesticides during early morning to avoid dew or late afternoon to avoid the hottest part of the day. Water plants 1-2 days before applying a pesticide. Always check the product label for the list of plants that may be injured by the pesticide.

Mention of commercial products is for educational purposes only and does not represent endorsement by Texas Cooperative Extension or The Texas A&M University System. Insecticide label registrations are subject to change, and changes may have occurred since this publication was written. The pesticide user is always responsible for applying products in accordance with label directions. Always read and carefully follow the instructions on the container label.

For more information on Texas insects and Entomology, see http://insects.tamu.edu


Table 1. Insecticide products, listed by mode of action, available for the control of Liriomyza leafminers in commercial greenhouse grown ornamental crops.

Class/ Mode of Action Classification Group 1

Common Name

Trade Name 2

R.E.I.

Manufacturer

Organophosphate/ Nerve Poison Group 1B

Acephate

Orthene 75 WP

24

Valent

PT 1300, Orthene TR

24

Whitmire MicroGen

Chlorpyrifos

PT DuraGuard ME

24

Whitmire MicroGen

Chlorpyrifos Pro 4

24

Micro Flo Company

Pyrethroid/ Nerve Poison Group 3

Bifenthrin

Talstar Flowable, Talstar Nursery Flowable, Talstar Nursery Granular

12

FMC

Lambda-cyhalothrin

Scimitar CS

24

Syngenta

Permethrin

Astro

12

FMC

Pyrethrin + Piperonyl butoxide - Nerve Poison Group 3

Pyrethrin

Diatect II Multipurpose Insect Control

12

Diatect International

Pyreth-it

12

Whitmire Micro-Gen

Pyrenone Crop Spray

12

Bayer

Neonicotinoid/Nerve Poison Group 4A

Imidacloprid

Marathon II

12

Olympic Horticultural Products

Marathon 1G

12

Olympic Horticultural Products

Thiamethoxam *

Flagship

12

Syngenta Professional Products

Spinosyn/ Nerve Poison Group 5

Spinosad

Conserve SC

4

Dow AgroSciences LLC

Avermectin/ Nerve Poison Group 6

Abamectin

Avid

12

Syngenta

Insect Growth Regulator/ Juvenile Hormone Mimic- Group 7C

Pyriproxyfen*

Distance

12

Valent

Pyrrole/ Metabolic Inhibitor Group 13

Chlorfenapyr *

Pylon

Olympic Horticultural Products

Insect Growth Regulator/ Chitin biosynthesis inhibitor Group 15

Novaluron

Pedestal (suppression only)

12

Crompton

Insect Growth Regulator/ Chitin biosynthesis inhibitor Group 17

Cyromazine

Citation

12

Syngenta Professional Products

Insect Growth Regulator/ Ecdysone agonist/molting disruptor Group 18B

Azadirachtin

Azatin XL Plus

4

Olympic Horticultural Products

Ornazin 3% EC

12

SePro

**leafminers not in label; use as appropriate

1 Based on Insecticide Resistance Action Committee International, mode of action classification v. 4.2.1, July 2005.

2 This list does not include all available product formulations, trade names are provided as examples