How to Manage Pests

UC Pest Management Guidelines


Cotton Leaf Perforator

Scientific Name: Bucculatrix thurberiella

(Reviewed 5/13, updated 5/13, corrected 10/16)

In this Guideline:

Description of the Pest

Cotton leaf perforator is a pest only in the southern desert areas of California. Early larval instars of the cotton leaf perforator are flattened, yellow to orange caterpillars that bore into leaves and tunnel between leaf surfaces until the fourth instar. They can be distinguished from maggots of leafmining flies by looking with a hand lens for the presence of a head capsule and mandibles. The fourth instar emerges from the leaf and begins skeletonizing leaves. During the molt between the fourth and fifth instar, the larva forms a thin silk shelter and curls into a horseshoe shape inside the shelter. The fourth and fifth instars are green to gray, with two black spots and several smaller white spots on each segment.


Leaves damaged by cotton leaf perforators have numerous windows, i.e., holes with a transparent membrane remaining on one side. Heavily infested leaves may be reduced to a network of veins. Most damage occurs in the top third of plants. Severe defoliation may cause bolls to open prematurely, and also cause shedding of squares and small bolls.


Any practice that reduces the use of insecticides lessens the chance of a perforator outbreak. Follow the management guidelines for other pests to avoid unnecessary destruction of natural enemies.

Cultural Control

Early harvest and plowdown will help reduce overwintering populations. The use of Bt cotton can also help reduce damage by this pest.

Organically Acceptable Methods

Cultural controls and sprays of the Entrust formulation of spinosad are acceptable for use on organically grown cotton.

Monitoring and Treatment Decisions

Cotton leaf perforator moths can be monitored with pheromone traps to detect adult populations several weeks before damage occurs. A 1-milligram dispenser placed in a delta trap and hung 1 to 2 feet above ground is effective for 4 weeks. Infestations of cotton leaf perforators usually begin at the edges of a field or in sandy streaks where plants are stressed. Check these areas first for damage to upper leaves. A treatment guideline suggested in Arizona is to treat when 25 to 50 % of the leaves in the top half of the plants have one or more exposed larvae. Count only those larvae on the leaf surface, including horseshoe stage larvae; don't count leafmining instars. The guideline applies only during the part of the season when plants have yet to set a significant part of their boll load. Look for live larvae, not just damage.

Treatment timing is critical because sprays cannot reach leafmining instars or horseshoe-stage larvae. If infestations are severe, wait until most larvae are in the horseshoe stage, then spray within 2 days to kill the fifth instars when they emerge from their shelters. Spot treat infestations that are limited to certain parts of the field.

Common name Amount per acre** R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, also consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
A. ALDICARB* 14 lb 48 90
  PERSISTENCE: Pest: Long NE:2 Short
  COMMENTS: Apply at layby by cultivation. Side-dress granules 8–16 inches to one side of the plant row, 2–6 inches deep. Do not graze or feed trash to livestock. Do not make more than 1 application at planting and 1 application after the crop has emerged. Six to 10-month plantback restrictions for crops not on label. Apply between March 1 and Sept. 1 only.
  (Asana XL) 5.8 fl oz 12 21
  SELECTIVITY: Low      
  PERSISTENCE: Pest: Long NE:2 Moderate
  COMMENTS: Do not graze or feed cotton forage. See label for plantback restrictions. Do not apply more than 0.5 lb a.i./acre during the growing season.
  (Steward) Label rates 12 14
  PERSISTENCE: Pest: Moderate NE:2 Moderate
  (Entrust)# 1.25–2 oz 4 28
  (Success) 4–6 fl oz 4 28
  PERSISTENCE: Pest: Moderate NE:2 Short
  COMMENTS: Use of Success allowed under a supplemental 24(c) label.
** Mix with sufficient water to provide complete 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.
# Acceptable for use on organically produced cotton.
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
2 NE = natural enemies



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cotton
UC ANR Publication 3444

Insects and Mites

  • L. D. Godfrey, Entomology, UC Davis
  • P. B. Goodell, UC IPM Program and Kearney Agricultural Research and Extension Center, Parlier
  • E. T. Natwick, UC Cooperative Extension - Desert Research and Extension Center, Imperial County
  • D.R. Haviland, UC Cooperative Extension, Kern County and UC IPM Program
  • V. M. Barlow, UC Cooperative Extension, Riverside County and UC IPM Program
Acknowledgment for contributions to Insects and Mites:
  • E. E. Grafton-Cardwell, Kearney Agricultural Research and Extension Center, Parlier
  • N. C. Toscano, Entomology, UC Riverside

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