Cotton Leaf Perforator

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.

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

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

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.