Species

Spinach Leafminer (Pegomya hyoscyami)

Related species

Spinach leafminer(Pegomya hyoscyami Panzer) and beet leafminer (Pegomya betae) are very similar species in behavior, appearance, plant hosts, and damage and generally cannot be distinguished in the field.

Host/site

Spinach leafminer, typically an early-season pest, may cause damage to early greens. It attacks members in the family Chenopodianceae, which includes crops like chard, beets, spinach as well as weeds like lamb's quarters and pigweed. The leafminer larva burrows between the layers of a leaf eating everything but the epidermis. Early damage is a slender, winding 'mine,' a tunnel, but later these expand and become blotches on the leaves. Inside the mine is a pale, white maggot.

Identification

Appearance

• Adults are slender gray flies about 6 mm long.
• Eggs are oval, white in color and less than 1 mm long.
• Larvae are small, white, flattened maggots up to 8 mm long. They tend to be pale green to whitish in color.

Indicators

Larvae feed between leaf surfaces, making winding mines at first, then widening and merging them to form large, tan or light- colored, dead, blotchy patches. These blotches are a strong indicator of insect damage. Since the maggot burrows within the leaf, holding an infested leaf to the light will reveal the insects. The remaining leaf is still edible.

Life cycle

Leafminers overwinter as pupae in the soil, hatching in late April and May. The adult fly then lays eggs on the underside of leaves that hatch in about 3-4 days. The eggs are laid in neat clusters and easy to spot if you scout by looking underneath the leaves. Tiny pale green to whitish maggots emerge and eat a slender, winding mine in between the two surfaces of the leaf Damage to crops begins and is the worst during the larvae stage. Maggots may migrate from leaf to leaf down a row. They become fully grown in just a few weeks and drop into the soil to pupate. The entire life cycle is 30-40 days with three to four generations per season. Typically mid-late May, late June and mid August are peak activity periods.
Natural Enemies

Monitoring

Regularly check young seedlings for leaf mines. Damage by leafminers can resemble symptoms produced by leaf spotting fungi. To differentiate, pull apart the blotchy area and look for a hollow area, like a tunnel, in the leaf or needle, which may expose either the insect and/or its droppings. Leaf spotting fungi cause these areas to collapse, without tunneling.

Action Thresholds

Most mines occur on the first true leaves. Some mines are more visible when seen from the underside of the leaf. Treat if you find more than an average of one mine per leaf in your overall field sample. If leafminer populations grow to a high level when seedlings have four to five leaves, removing plants may be the best option to prevent further spread of the pests.

Cultural and Physical Controls

• Weed control and crop rotation are the first line of defense.
• Remove infested leaves and weeds as soon as noticed and place in the garbage.
• Using "floating row covers" should help if screens are in place before flies emerge and if the crop is in a different area of the garden from the previous year.
• Remove weed hosts including lambsquarter, nightshade, chickweed and plantain.

Biological Controls

• Natural enemies, especially parasitic wasps, commonly reduce populations of leafminers.
• Allowing chickens to roam in areas where leafminers have been present can help.

Chemical Controls

Not reccomended.

References

"Beet or Spinach Leafminer in Home Gardens." WSU Gardening in Western Washington. Web. 31 May 2010. <http://gardening.wsu.edu/library/inse008/inse008.htm>.

Ghidiu, Gerald. Fact Sheet. Spinach Leafminer. Rutgers University, 8 July 1995. Web. 31 May 2010. <http://njaes.rutgers.edu/pubs/publication.asp?pid=FS276>.

Hazzard, R., and J. Capinera. "Leafminer, Beet—Insects-UMass Extension." Agriculture and Landscape—UMass Extension. Web. 31 May 2010. <http://www.umassvegetable.org/soil_crop_pest_mgt/insect_mgt/beet_leafminer.html>.

"Home Garden Small Fruit, Vegetables and Tree Fruit: Vegetables - Radish to Spinach." PNW Insects - Vegetables - Radish to Spinach. Web. 31 May 2010. <http://webcache.googleusercontent.com/search?q=cache:FQo_pJUFoZQJ:insects.ippc.orst.edu/pnw/insects%3F26HGDN17.dat+Spinach+Leafminer+biological+controls&cd=3&hl=en&ct=clnk&gl=us&client=firefox-a>.

"Identification Keys: Insects: Spinach Leafminer." The University of Idaho College of Agricultural and Life Sciences. University of Idaho. Web. 31 May 2010. <http://www.cals.uidaho.edu/edComm/keys/plates/plate72.htm>.

"New England Vegetable Management Guide - Spinach - Insect Control." New England Vegetable Management Guide - New England Vegetable Management Guide. Web. 31 May 2010. <http://www.nevegetable.org/index.php/crops/spinach?start=3>.

Wilson, Carl. "Leafmining Insects." Colorado State University Extension. Web. 31 May 2010. <http://www.ext.colostate.edu/pubs/insect/05548.html>.