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How to Manage Pests

UC Pest Management Guidelines


Adult vegetable leafminer.

Dry Beans

Leafminers

Scientific name: Liriomyza sativae and Liriomyza trifolii

(Reviewed 8/07, updated 12/08)

In this Guideline:


DESCRIPTION OF THE PESTS

Leafminer adults are very small flies, 0.1 inch (2.5 mm) long, black to blue, with parts of the thorax, legs, and abdomen yellow. Usually there is a prominent yellow area at the base of the wings. The minute white eggs are laid just under the leaf epidermis and hatch in 4 to 6 days. Maggots are normally concealed between leaf surfaces in the mines where they feed; they range from yellow to white, are 0.25 to 0.33 inch long, blunt at the rear end, and pointed in front. Pupation occurs in the mines or in the ground. During summer, the life cycle requires about 23 days. There are from three to five generations a year.

DAMAGE

Leafminers are occasionally a problem in beans generally during the latter part of the production season. The maggots feed between the upper and lower leaf surfaces causing large whitish blotches, or in the case of serpentine leafminers, slender, white, winding trails through the interior of the leaf.

MANAGEMENT

Biological Control
Because of numerous common parasites, leafminers are generally not serious pests, but can be sporadic in their damage. The destruction of beneficial insects by frequent applications of insecticides applied to control other pests can result in leafminer outbreaks. Of the numerous parasites that attack leafminers in California, the most abundant is the parasitic eulophid wasp, Solenotus intermedius, but Diglyphus spp. and Chrysocharis spp. are probably the most important for controlling leafminers.

Organically Acceptable Methods
Biological control and sprays of the Entrust formulation of spinosad are organically acceptable.

Monitoring and Treatment Decisions
To check for leafminers, evaluate the amount of mining in the leaves during weekly observations for other insect pests beginning at crop emergence. Continue to monitor leaves during vegetative growth, flower bud to bloom, and pod fill periods. Economic thresholds have not been determined on all bean varieties. On pinks and kidneys, treat if 25% of the surface of older leaves is mined and mines are present in the new leaves.

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 the impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. SPINOSAD
  (Entrust)# 1.5–2 oz 4 28
  (Success) 4.5–6 oz 4 28
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Do not apply more than 12 oz/acre/season of Success or 3.75 oz/acre/season of Entrust. For blackeyes, be sure to apply with an oil.
 
B. CYROMAZINE
  (Trigard) 2.66 12 7
  MODE OF ACTION GROUP NUMBER1: 17
  COMMENTS: Not for use on cowpeas.
 
** Mix with sufficient water to obtain full coverage.
+ 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 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 the 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). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
R. F. Long, UC Cooperative Extension, Yolo County

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