Description of the Pest
Citrus cutworm has only one generation per year. The grayish citrus cutworm moths emerge from early January to the end of April, with peak emergence during March. After mating, female moths lay their round, milky white eggs mainly on the upper side of new leaves in clusters of 40 to 225. After a few days, eggs turn dark in color as larvae develop inside; they hatch in 5 to 10 days. Young larvae are usually light green in the first three instars and pinkish or brown in the fourth and fifth. All but the youngest larvae have a whitish stripe along each side of the body. The skin appears smooth to the naked eye; it does not have conspicuous hairs or tubercles. When disturbed, older larvae curl up and drop to the ground.
Larvae mature in 3 to 6 weeks: the greatest number of larvae are usually found from mid-March to the first of May. Mature larvae drop to the ground and pupate in soil. Pupae remain dormant until the following spring.
Damage
Citrus cutworm move around while feeding, usually taking a few bites from numerous leaves, blossoms, or fruit. Young larvae feed mostly on the edges of tender leaves; older larvae eat holes through leaves and blossoms and into fruit. A smaller number of citrus cutworms cause more damage than larger numbers of other caterpillars because they are larger and move throughout the tree during feeding. Mature fruit are rarely attacked.
Management
Citrus cutworm is primarily a pest of plums in the San Joaquin Valley, but even there it is not a pest in all orchards or every year. Monitor carefully in spring in areas where it has been a problem.
Biological Control
Two parasites attack citrus cutworm larvae and are effective in reducing the next year's population. Ophion sp., a parasitic wasp, attacks cutworms just before they are ready to mature. The parasitized larva pupates in the soil where it is consumed by the parasite larva. Another parasitic wasp, Banchus sp., also attacks cutworm larvae.
Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are organically acceptable management tools.
Monitoring and Treatment Decisions
Monitor orchards weekly from mid-bloom until after petal fall to determine if citrus cutworm is a problem. The most critical period is late bloom to post petal fall when cutworm larvae are attracted to the small developing fruit. If populations appear to be increasing, monitor weekly until the majority of the population has pupated. Either search for larvae or shake foliage vigorously while holding it over a sweep net to monitor this pest.
| Common name | Amount to use** | REI‡ | PHI‡ | ||
|---|---|---|---|---|---|
| (Example trade name) | (conc.) | (dilute) | (hours) | (days) | |
| Not all registered pesticides are listed. 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, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used. | |||||
| A. | BACILLUS THURINGIENSIS ssp. KURSTAKI# | ||||
| (various products) | Label rates | — | 4 | 0 | |
| MODE OF ACTION GROUP NUMBER1: 11.B2 | |||||
| COMMENTS: Timing is important because of short residual period. Apply only during warm dry weather to control young actively feeding worms. Because larvae hatch over a period of 1–2 months, this material will have to be applied more than once. Good coverage is essential. | |||||
| B. | SPINOSAD | ||||
| (Entrust)# | 1.25-2.5 oz | 0.3-0.6 oz | 4 | 7 | |
| (Success) | 6–8 oz | 1.5–2 oz | 4 | 7 | |
| MODE OF ACTION GROUP NUMBER1: 5 | |||||
| COMMENTS: Most effective when applied at petal fall. | |||||
| C. | PHOSMET | ||||
| (Imidan) 70WP | 4.25 lb | 1 lb | 3 days | 7 | |
| MODE OF ACTION GROUP NUMBER1: 1B | |||||
| ** | For dilute applications, rate is per 100 gal water to be applied in 300–500 gal water/acre, according to label; for concentrate applications, use 80–100 gal water/acre, or lower if the label allows. |
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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. |
| # | Acceptable for use on organically grown produce. |
| — | Not recommended or not on label. |
| 1 | Rotate insecticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). |