Description of the Pest
The Diaprepes abbreviatus is a large, colorful weevil, 3/8 to 3/4 inch (10–19 mm) long, with numerous forms or morphs, ranging from gray to yellow to orange and black. The diaprepes root weevil is about twice the size of Fuller rose beetle. Unlike Fuller rose beetle, it can fly (though it often prefers to crawl), and it is a sexual species (mating is required for female egg production). An adult female weevil lays clusters of eggs in leaves that are folded and glued together. The eggs hatch in 7 to 10 days, and the newly emerged larvae drop to the soil. The larvae enter the soil and feed on the roots of plants for 9 to 18 months, molting 10 to 11 times. The larvae then pupate in the soil. After irrigation or rain events, adults will emerge, mate, and the life cycle begins again.
This weevil is native to the Caribbean region. In 2005 two isolated populations were found in Newport Beach (Orange County) and Long Beach (Los Angeles County). The beetle was also found in San Diego County in 2006 and is slowly expanding its range in coastal southern California.
Diaprepes root weevil will feed on about 270 different plants, including citrus (all varieties), hibiscus, palm, birch, roses, guava, loquat, holly, and other ornamentals. Because of its broad host range, the diaprepes root weevil poses a great threat to citrus and ornamental plant industries and potentially other crops in California.
Damage
The diaprepes root weevil damages both the leaves and the roots of plants. The adult weevils damage leaves by chewing semi-circular areas out of the leaf margin. There may also be frass or weevil droppings near the areas that have been fed upon. The grub-like larva feeds on the roots of a plant, weakening or killing a plant.
Management
Treat every life stage with at least one application per season from each section of the following list. There are no pesticides for pupae.
Adults (Apply in 100–300 GPA, Outside Coverage)
Apply two soil applications of bifenthrin (Brigade) timed to coincide with adult emergence from the soil. Or use foliar applications of fenpropathrin (Danitol), zeta-cypermethrin (Mustang), carbaryl, or a single application of beta-cyfluthrin (Baythroid).
Larvae
Apply imidacloprid (Admire Pro or generic formulations) or thiamethoxam (Platinum) when root growth is occurring. California regulations limit treatment timing to between petal fall and Dec 6. Imidacloprid remains effective for 4 to 5 months. It requires 3 to 4 weeks for uptake into mature citrus to begin to kill pests. For optimum uptake, apply to trees through drip, microsprinkler, or low-pressure irrigation systems. Emitters must provide even, uniform distribution of water. Lightly pre-wet the soil for several hours before the application to break the soil surface tension. Once the irrigation system reaches operating pressure, inject the insecticide into the system over a calculated time interval (generally 2 hours) to allow uniform distribution throughout the system. The use of a dye marker in the treatment solution is recommended to determine when lines are clear of the insecticide. Once the solution has cleared all irrigation lines and emitters, continue irrigation to move the insecticide into the active root zone but do not overirrigate or cause runoff. Wait 24 hours before subsequent irrigations.
There are two species of nematodes, Heterorhabditis indica and Steinernema riobravis, that will attack and kill diaprepes root weevil. Entomophagous nematodes are exempt from U.S. EPA registration under FIFRA because they are whole-organism biological control agents. Therefore, they can be used in most settings where diaprepes larvae may exist. Once the nematodes kill most of the diaprepes larvae in an area, they die from a lack of food. They will not feed on plants. Because these are living organisms, they work best in the following situations:
- Fairly loose-textured soil, such as sand, loamy sand, or sandy loam. The nematodes need to be able to move through the water found in the spaces between the soil particles. Clay soils tend to have very small spaces between the soil particles, whereas the looser textured soils tend to have larger spaces.
- Moist soil (not over-saturated); irrigate the area to be treated before applying nematodes.
- Soil temperatures between 60 and 85°F.
Eggs
Apply diflubenzuron (Micromite) to prevent egg hatch when the adults are actively depositing eggs in spring through summer. Micromite is more effective if applied with oil, which helps to dissolve the substance the weevil uses to glue leaves together when it deposits eggs.
For more information, read Diaprepes Root Weevil, UC ANR Publication 8131.
| Common name | Amount to use | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (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. | ||||
| GROUND SPRAYS | ||||
| A. | BIFENTHRIN | |||
| (Brigade WSB) | 40–80 oz/acre | 12 | 1 | |
| RANGE OF ACTIVITY: Pests: broad (many insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: intermediate; Natural enemies: long | ||||
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: Do not apply in the vicinity of aquatic areas. Apply only to the soil when adults are emerging and do not allow the insecticide to contact fruit or foliage. | ||||
| FOLIAR SPRAYS | ||||
| A. | FENPROPATHRIN | |||
| (Danitol 2.4 EC) | 16–21.33 fl oz/100–300 gal water/acre | 24 | 1 | |
| RANGE OF ACTIVITY: Pests: broad (many insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: intermediate; Natural enemies: long | ||||
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: Use only on citrus trees 3 years or older. Do not apply in the vicinity of aquatic areas. | ||||
| B. | BETA-CYFLUTHRIN | |||
| (Baythroid XL) | 2.4–3.2 oz/100–300 gal water/acre | 12 | 0 | |
| RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most | ||||
| PERSISTENCE: Pests: intermediate; Natural enemies: intermediate (low rates), long (high rates) | ||||
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: Apply only once per crop season. Do not apply in the vicinity of aquatic areas. | ||||
| C. | ZETA-CYPERMETHRIN | |||
| (Mustang) | 4.3 oz/20 gal (concentrated) or 100 gal (dilute) water/acre | 12 | 1 | |
| RANGE OF ACTIVITY: Pests: broad (many insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: intermediate; Natural enemies: intermediate | ||||
| MODE-OF-ACTION GROUP NUMBER1: 3A | ||||
| COMMENTS: For use on all varieties. Do not apply in the vicinity of aquatic areas. | ||||
| D. | CARBARYL* | |||
| (Sevin XLR Plus) | 5 qt/100–500 gal water/acre | See label | 5 | |
| RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most | ||||
| PERSISTENCE: Pests: long; Natural enemies: long | ||||
| MODE-OF-ACTION GROUP NUMBER1: 1A | ||||
| …PLUS… | ||||
| 415 NARROW RANGE OIL | ||||
| (various products) | 0.5% | See label | See label | |
| RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: short; Natural enemies: short | ||||
| MODE OF ACTION: Contact including smothering and barrier effects; also improves translaminar movement and insecticide persistence. | ||||
| COMMENTS: May increase citrus red mite numbers. Caution: Serious hazards are associated with oil sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval. | ||||
| E. | DIFLUBENZURON | |||
| (Micromite 80WGS) | 6.25 oz/100–500 gal water/acre | 12 | 7 | |
| RANGE OF ACTIVITY: Pests: intermediate (katydids, peelminer, leafminer, grasshoppers); Natural enemies: predatory beetles | ||||
| PERSISTENCE: Pests: intermediate; Natural enemies: intermediate | ||||
| MODE-OF-ACTION GROUP NUMBER1: 15 | ||||
| …PLUS… | ||||
| 415 NARROW RANGE OIL | ||||
| (various products) | 0.25–1% | See label | See label | |
| RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: short; Natural enemies: short | ||||
| MODE OF ACTION: Contact including smothering and barrier effects; also improves insecticide spread and persistence. | ||||
| COMMENTS: Apply when the adults are actively depositing eggs. This insecticide will help to prevent egg hatch. | ||||
| SOIL-APPLIED SYSTEMIC APPLICATIONS | ||||
| A. | IMIDACLOPRID | |||
| (Admire Pro) | 7 fl oz/acre | 12 | 0 | |
| RANGE OF ACTIVITY: Pests: narrow (aphids, glassy-winged sharpshooters, Asian citrus psyllid, citrus leafminer, weevils, whiteflies); Natural enemies: predatory beetles and parasites | ||||
| PERSISTENCE: Pests: long; Natural enemies: intermediate | ||||
| RESISTANCE: Some glassy-winged sharpshooter populations | ||||
| MODE-OF-ACTION GROUP NUMBER1: 4A | ||||
| COMMENTS: Effective against Asian citrus psyllid on young trees; levels of imidacloprid taken up by bearing trees are not sufficient to be consistently effective against Asian citrus psyllid. California regulations limit treatment timing to between petal fall and Dec 6. Many generic formulations of imidacloprid are available and are effective. Review and follow the California neonicotinoid regulations effective January 1, 2024. These regulations include restrictions on treatment timings and rates, along with information on how to be exempt from those restrictions when treatments are made for a quarantine pest. |
||||
| B. | THIAMETHOXAM | |||
| (Platinum 75 SG) | 2.67–3.67 oz/acre | 12 | 0 | |
| RANGE OF ACTIVITY: Pests: narrow (sucking insects); Natural enemies: predatory beetles and parasitic wasps | ||||
| PERSISTENCE: Pests: long; Natural enemies: intermediate | ||||
| MODE-OF-ACTION GROUP NUMBER1: 4A | ||||
| COMMENTS: Do not between February 10 and petal fall. Review and follow the California neonicotinoid regulations effective January 1, 2024. These regulations include restrictions on treatment timings and rates, along with information on how to be exempt from those restrictions when treatments are made for a quarantine pest. |
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| ** | OC - Outside coverage uses 100 to 250 gal water/acre. |
| ‡ | 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. |
| 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their website at http://irac-online.org/. |
| * | Permit required from county agricultural commissioner for purchase or use. |