Pest Of The Month: Celery Leaftier
August 1, 2012 
Identification
Celery leaftier is found throughout the U.S. as well as Central and South America. Its eggs are tiny, round, and slightly flattened. The shiny white eggs grow darker as they mature. The eggs are deposited on the underside of leaves singly or in small groups of up to 12.
The larva is a small, greenish-yellow ¾-inch long caterpillar that feeds on the lower surface of leaves, often rolling leaves or webbing them together with a thin layer of silk. There are five larval instars. Like other webworms, larvae have a tendency to retreat into their webbed shelter or to wriggle violently and spin down from the plant on a strand of silk if disturbed. Small larvae feed on leaves. But as they grow, they may move to the upper portions of the petiole. Petiole damage looks like cutworm or looper damage with circular depressions and hollowed out tissue. Tied leaves, webbing, and the presence of the larvae are contaminants at harvest.
The adult is a small brown moth resembling a European corn borer, except that it is smaller and has a “snoutlike” mouthpart. The moths are nocturnal, and remain hidden during the daylight hours although they may rise in large numbers when disturbed.
Survival And Spread
In Florida, key weedy host plants for celery leaftier are redroot pigweed and spiny amaranth. These and several other weed hosts are important in maintaining leaftiers through the summer period. Under ideal conditions, the celery leaftier may complete its life cycle in a month. Under field conditions, development is delayed by cooler weather and a generation may take two months in the spring and autumn, and more than three months during the winter.
Pupation normally takes place in a thin silk cocoon among folded leaves. The pupa is smoky brown. Studies in Florida documented the importance of several insect parasitoids including the egg parasite Trichogramma sp. Birds also are predators of celery leaftier in Florida.
Management Methods
Destruction of crop debris is an important cultural control. Studies in Virginia indicated that treatment is warranted if there are more than four weeks before harvest and there are two or more larvae per 100 plants.
Traps can be useful for population monitoring. Foliar insecticides are applied for leaftier suppression, and growers should target the young larvae for control because they are easier to kill. This insect is only occasionally threatening, however. Small larvae can be controlled with Bt products, but larger larvae may be more difficult to control.
For organic growers, two applications of pyrethrum provide good control. The first application will flush tiers from their webs, the second should kill them.
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