Artichoke Plume Moth

Adults of the artichoke plume moth vary in color from buff to brownish-buff, with a wing expanse of 0.75 to 1.25 inch (18–31 mm). Both fore and hind wings are divided into lobes, giving the appearance of several pairs of wings; the hind wings are fringed.

The sex ratio of adult moths is 1:1, and females lay an average of 245 eggs. Eggs are usually laid singly on the underside of leaves and occasionally on the bud stalk. The freshly deposited eggs are light greenish-yellow, turning darker (orange-yellow) with age, shiny, and very small (about 0.02 inch or 0.5 mm).

Upon hatching, first instar larvae are about 0.04 inch (1 mm) long and pale yellow. When feeding on frond leaves of vegetative shoots, the young larvae tend to feed externally. After the first molt, larvae start tunneling into the leaf stalk. Some newly hatched larvae, however, may enter into the leaf veins immediately after hatching and move toward the leaf petiole, completing the entire larval stage within the leaf. If the eggs are deposited on leaves close to the buds or directly on the bud stalks, the newly hatched larvae move toward the buds and mine the outer bracts. With each subsequent molt, the larvae work their way toward the center of the bud.

Larvae undergo four to five instars. The larvae between the first and the last instars resemble the first in color and markings, differing only in size. Larvae in the last instar, however, are more off-white, turning yellowish to pink at maturity, and reach about 0.6 inch (1.5 cm) in length. The prothoracic shield, anal plates, true legs, and bases of primary setae become quite prominent in this instar. When close to pupation, larvae cease feeding, emerge out from the feeding site, and generally drop to the ground. Prepupae are very active in the early part of the stage and wander around in search of a suitable pupation site. Pupation generally occurs in plant debris, very often among folds of dried up leaves. The elongate pupae are pale yellowish-brown, turning darker with age. The abdomen shows longitudinal lines and distinct toothlike spines that project backwards.

There are three to four overlapping generations of the plume moth a year. The various developmental stages of the plume moth have different temperature thresholds for their development. In the mild climate zone of the central coast of California, the very low (35°F, 1.5°C) developmental threshold of the last larval instar enables the pest to continue its development throughout the year. At a temperature threshold of 45°F (7°C), the pest needs 856 ± 70°F (476 ± 39°C) degree-days to complete one generation.

Larvae will feed on any part of the plant, but the economic damage occurs when they feed on the floral buds and render them unmarketable. Occasionally plants are damaged when the larvae feed in the developing plant shoots; damaged shoots, however, often recover. Larvae may also bore into the crown below the soil surface. If infested crowns are used for vegetative propagation, the pest will establish itself quickly in the newly planted field.

Artichoke plume moth is primarily a problem where artichokes are grown as perennials, and thus is mainly a problem in California's central coast. Artichokes are normally grown as annuals in southern California. Management of artichoke plume moth in established perennial artichoke fields is divided into two periods that utilize different management regimes. The two periods are the summer (from stalk cutback until September) and the winter ditch period (from September to May). During the summer period, artichokes are growing vegetatively and are irrigated on a 3-week schedule. Following irrigation, fields are cultivated, and if needed, insecticides can be applied by ground rig. During the winter ditch period, insecticide treatments must be applied by air. Need for treatment is determined by pheromone trap catches and field monitoring.

Natural enemies, especially parasitic wasps, attack the artichoke plume moth. Most of the parasites attack the larvae. However, these parasites are seldom important in control because the larva spends most of its time feeding within the plant, protected from natural enemies.

Sanitation can be an important factor in plume moth population dynamics. By cutting off the plants 2 or 3 inches below soil level, shredding the tops, and incorporating the plant materials into the soil, artichoke plume moth infestations in perennial fields can be reduced by about 95%. However, the movement of the adults between fields makes the impact on any given field very temporary. Cut back stalks from mid-April to mid-June in fields scheduled for fall, winter, and spring harvests. Stalk cutback is carried out in August to September for summer-harvested fields. Try to avoid growing summer-harvested artichokes near artichoke fields that are cut back in summer because the cut fields will provide a reservoir of invading moths.

The way in which the infested artichokes are handled during harvesting is important, especially in early spring months. As they work in the fields, harvest crews should be able to identify infested buds, pick them immediately, regardless of stage of maturity, and remove them from the field.

Biological and cultural control, preplant soaks of Steinernema carpocapsae, and in-season sprays of Bacillus thuringiensis (when applied by itself) or the Entrust formulation spinosad are acceptable for use on organically certified crops. Mating disruption is being used in some fields to reduce insecticide use.

When planting or replanting an artichoke field, consider soaking replant stumps in a solution of the entomopathogenic nematode, S. carpocapsae. If done correctly, this can reduce plume moth infestations to less than 1% and reduce the number of treatments required during the first year.

Use pheromone traps to detect adult plume moth activity; trap catches of seven or more moths per week may indicate an impending problem. An organized record of weekly trap catches and daily temperature data converted to degree-days can be used to predict peak adult emergence.

Examine leaves weekly during summer, fall, and spring for eggs. Eggs are difficult to see, and some experience is required to make an accurate egg count. A count of one egg per 50 leaves indicates that there might be sufficient eggs present to produce an economic infestation.

Also, sample individual shoots weekly to look for plume moth larvae. Determine the percent shoot infestation by sampling at least 50 shoots. An infestation of 3% or more requires treatment. Timing is critical: target the treatment against the first instar larvae.

The most effective insecticides for artichoke plume moth control are those that kill the adult moths and the larval stage. Because the materials listed below have potential resistance problems, Bacillus thuringiensis can be added to the tank mix to reduce the risk of resistance development. By itself, however, Bacillus thuringiensis does not normally provide sufficient control because it is only effective against young larvae and does not kill adult moths.