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How to Manage Pests

UC Pest Management Guidelines


Adult vegetable leafminer.

Celery

Leafminers

Scientific Names:
Serpentine leafminer: Liriomyza trifolii
Pea leafminer: Liriomyza langei
Vegetable leafminer: Liriomyza sativae

(Reviewed 10/05, updated 6/08)

In this Guideline:


DESCRIPTION OF THE PESTS

Adults are small black to gray flies with yellow markings. Females puncture leaves to feed on plant sap and lay eggs within the leaf tissues. After 2 to 4 days eggs hatch and larvae feed between the upper and lower surface of the leaves, making distinctive winding, whitish tunnels or mines that are often the first clue that leafminers are present. Larvae emerge from the mines and pupate on the leaf surface or, more commonly, in cracks in the soil. Many generations occur each year and the entire life cycle can be completed in less than 3 weeks when the weather is warm.

The species can be separated on the basis of the adult's appearance or by the appearance of the mines. The serpentine leafminer is most common in the warmer, celery-growing areas of southern California and the Central Valley; it does not occur in Central Coast growing areas. The pea leafminer occurs in the Salinas Valley as well as in the central coast growing areas where it occurs with the serpentine leafminer. It also appears to be extending its distribution into the southern growing regions of the state. The vegetable leafminer may be present in the coastal areas in low populations.

The serpentine leafminer is the smallest and most yellow of the three and produces characteristically wandering mines. The pea leafminer is the largest and most black or gray and, following the first two instars, produces straight mines. The pea leafminer is more likely to mine the petioles and stalks of celery than the other species.

DAMAGE

Leafminers can reduce the plant's photosynthetic capacity, render edible portions of the plant unmarketable, and provide an entrance for disease organisms. In addition, many countries and some states regulate the importation of produce grown in areas where pea leafminer exists to prevent its introduction.

MANAGEMENT

Biological Control
Natural enemies, especially parasitic wasps in the genus Diglyphus, commonly reduce populations of leafminers, unless killed off by insecticides applied to control other pests. Several other parasites also attack leafminers. Predators are not important biological control agents because leafminer eggs and larvae are protected within leaf tissue. Choose selective pesticides for treating other pests, if possible, to avoid killing parasites and inducing leafminer outbreaks.

Cultural Control
Liriomyza leafminers attack a wide variety of vegetable crops often grown in proximity to celery. Where possible, avoid planting next to infested fields, especially lettuce fields near harvest.

Organically Acceptable Methods
Biological and cultural controls and sprays of azadirachtin (Neemix) are acceptable for use on organically grown produce.

Monitoring and Treatment Decisions
Treatment thresholds must be based on the species involved. To measure infestation levels of the serpentine leafminer, place trays between the rows of celery to catch dropping pupae. Trays about 4 inches by 9 inches fit well between the rows. Catches of 15 pupa or more per day per tray may be indicative of populations that require treatment.

Populations of pea leafminer or vegetable leafminer are not as easily monitored, and the treatment threshold is probably considerably lower than for the serpentine leafminer because of the tendency of this species to mine the stalks.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to water quality and impact on natural enemies and bees. Not all registered pesticides are listed. Always read label of product being used.
 
A. ABAMECTIN*
  (Agri-Mek) 0.15EC 8 to 16 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: A larvacide. Best control is obtained when 2 applications are applied 7–10 days apart.
 
B. CYROMAZINE
  (Trigard) WP 0.166 lb (one packet) 12 7
  MODE OF ACTION GROUP NUMBER1: 17
  COMMENTS: Do not make more than 2 sequential applications or 6 applications to one crop of celery.
 
C. OXAMYL*
  (Vydate L) 1–2 qt 48 21
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Larvacide. May not effectively control serpentine leafminer. Do not apply more than 3 gal/acre/season.
 
D. SPINOSAD
  (Entrust)# 2–3 oz 4 1
  (Success) 6–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Is less effective on pea leafminer (L. langei) larvae than on other leafminers. Effective as a wet spray against all leafminer adults. Do not apply more than 9 oz of Entrust or 29 fl oz of Success/acre/crop.
 
E. SPINETORAM
  (Radiant) SC 6–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Effective on L. sativae and L. trifolii, but may not be effective for L. langei.
 
F. AZADIRACHTIN#
  (Aza-Direct) 1–2 pt 4 0
  (Neemix) 4.5% 4–7 oz 12 0
  MODE OF ACTION GROUP NUMBER1: 18B
  COMMENTS: Kills leafminer after pupation. Although OMRI approved, check with certifier for any restrictions that apply.
 
G. PYRETHRIN/ROTENONE
  (Pyrellin E.C.) 1–2 pt 12 12 hours
  MODE OF ACTION GROUP NUMBER1: 3 and 21
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.
# Acceptable for use on organically grown produce.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Celery
UC ANR Publication 3439
Insects
L. D. Godfrey, Entomology, UC Davis
J. T. Trumble, Entomology, UC Riverside
Acknowledgement for contributions to Insects:
W. E. Chaney, UC Cooperative Extension, Monterey County

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