A New Pest in California, Diaprepes Root Weevil (Citrus Root Weevil): Provisional Treatment Guidelines for Citrus in Quarantine Areas

The Diaprepes root weevil, Diaprepes abbreviatus (Coleoptera:Curculionidae), 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. This weevil is native to the Caribbean region and was accidentally introduced into Florida in the 1960s, where it has caused extensive damage. It has been intercepted in shipments of plants to California, and 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. The California Department of Food and Agriculture (CDFA) has established quarantine zones in Newport Beach and Long Beach and several areas in San Diego County to control this pest and prevent it from spreading.

This 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.

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. 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 several months. The larvae then drop to the soil. The larvae enter the soil and feed on the roots of plants for several months. The larvae then pupate in the soil. After the appropriate amount of time, adults will emerge and the life cycle begins again.

If you are outside the quarantine areas listed above and see the adult weevils or have damage to plants you suspect is caused by the weevil, please contact the CDFA Exotic Pest Hotline at 1-800-491-1899. Personnel from CDFA will inspect plants for the presence of the Diaprepes root weevil and send any specimens collected to the CDFA diagnostic laboratory for identification.

The following treatment guidelines have been developed for citrus growers within the quarantine zones. Treat every life stage with at least one treatment from each section of the following list per season. Continue treatments until no life stages are found for a full year.

Adults (apply in 100-300 gpa, outside coverage)

• Brigade WSB (bifenthrin*) use 40 oz/acre. Apply two applications that are timed to coincide with adult emergence. Do not allow insecticide to contact fruit or foliage or apply more than 80 oz/acre/year.
• Danitol 2.4 EC (fenpropathrin*) use 16-21 oz/acre. Use only on citrus trees 3 years or older. Do not apply in the vicinity of aquatic areas and do not apply more than 21.33 fl oz/acre/year.
• Sevin 80S (carbaryl*) use 5-10 lb + 0.5% oil/acre. For use on all varieties. Do not apply during bloom or exceed 25 lb/acre/application. May increase citrus red mite populations. Caution: Serious hazards are associated with oil treatments to green lemons because of phytotoxicity after sweating; check label for preharvest interval.
• Sevin XLR (carbaryl*) use 1-2 gal + 0.5% oil/acre. During the bloom period, apply from 1 hour after sunset until 2 hours before sunrise. XLR Plus formulation is less toxic to honey bees than the 80S formulation when direct application to bees is avoided and the spray residues have dried.
• Baythroid 2E (cyfluthrin*) use 6.4 oz/acre. Only a single application may be made per crop season. Do not apply within 25 feet of lakes, reservoirs, rivers, permanent streams, marshes, or natural ponds, estuaries, and commercial fish farm ponds.
• Kryocide 96 WP or Prokil Cryolite 96 (cryolite) use 8-10 lb/acre. This slow-acting stomach poison may take several days of warm weather to kill beetles. Do not exceed 90 lb/acre/season. These are less effective than the pyrethroid and carbamate insecticides but would be useful in situations where carbamates and pyrethroids could not be used.

Larvae

• Admire Pro (imidacloprid) use 14 fl oz/acre through the irrigation system. Apply when root growth is occurring. Apply to soil; remains effective 4-5 months. Requires 3-4 weeks for uptake into mature citrus to begin to kill pests. Pre-wet soil before treatment is applied. Very toxic to bees; do not apply during bloom because bees may be drawn to irrigation water. For optimum uptake, apply to newly planted trees or trees irrigated by drip/microsprinkler/low-pressure irrigation systems. Emitters must provide even, uniform distribution of water. Lightly pre-wet soil for several hours before application to break soil surface tension. Once the irrigation system reaches operating pressure, inject the treatment 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 treatment. 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.
• Nematodes. There are two species of nematodes that will attack and kill Diaprepes root weevil. They are both available commercially and 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 all 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.
  • They work best in a moist soil (not over-saturated). It is usually recommended that the area to be treated is irrigated before application of the nematodes.
  • They work best in a soil with a temperature above 60-65°F, but less than 85°F. Remember this is soil temperature, not air temperature.
• Symbion, Heterorhabditis indica. This nematode is applied at a rate of 20,000 nematodes per sq. ft. The minimum days to harvest is 0 days. This product is listed by the Organic Material Review Institute, which means that this product can be used in certified organic plantings (that is, meets all requirements of the National Organic Program). This nematode is available from Biocontrol Systems, located in southern Ohio. The label for the product can be viewed at www.nematodary.com, and the product can be purchased from the Web site or by calling 1-888-793-IBCS (toll free). The nematodes come in three package types and can treat from 300 sq. ft. to 6,000 sq. ft. The nematodes packaged in the syringe pack may not be the best choice for treatment of Diaprepes. The sponge or pouch packaging may work better for the California situation.
• BioVector, Steinernema riobrave. This nematode is applied at a rate of 20,000 to 40,000 nematodes per sq ft., depending upon soil type for citrus groves and ornamental plantings in the ground. The minimum days to harvest is 0 days. The label for this product can be found at www.beckerunderwood.com. The company that grows this nematode markets it through Western Farm Service in southern California. The contact is Tim at (714) 334-3444. If that doesn't work, the western U.S. representative for this company is Greg Wall, phone: (925) 519-2193.

Eggs

• Micromite 80 WGS (diflubenzuron*) use 6.25 oz + 0.5% oil/acre. Apply when the adults are actively depositing eggs. This insecticide will help to prevent egg hatch. 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. Registered for oranges, grapefruit, and tangerines with a section 18 for lemons pending.

Pupae: No known treatment

For more information, read UC ANR Publication 8131: Diaprepes Root Weevil.

* Restricted use material. Permit required from County Agricultural Commissioner for purchase or use.