How to Manage Pests

UC Pest Management Guidelines

Strawberry

Root Beetles

Scientific Names:
Black vine weevil: Otiorhynchus sulcatus
Cribrate weevil: Otiorhynchus cribricollis
Fuller rose weevil: Pantomorus cervinus
Woods weevil: Nemocestes incomptus
Hoplia beetle : Hoplia dispar, H. callipyge

(Reviewed 6/08, updated 6/08)

In this Guideline:


DESCRIPTION OF THE PESTS

Root beetles are occasional problems on California strawberries primarily in nonfumigated and/or second-year plantings in the San Joaquin Valley. They feed at night and hide around the crowns of plants during the day and, with the exception of adult hoplia beetles, they cannot fly. The adults, nearly all females, emerge in late spring or summer, feed on strawberry foliage, and lay their eggs around the crowns about 1 month after emergence. After hatching, the larvae work their way into the soil and feed on strawberry roots and crowns through the fall.

Root weevil larvae have curved, white or pink bodies that are about 0.38 inch (9 mm) long when fully grown. They have distinct brown heads and no legs. In spring, they resume feeding and can cause extensive damage before they pupate. Root weevils have a single generation each year. The Fuller rose weevil can be distinguished from the other weevils by an oblique, white band on the side of each wing cover. In addition, their larvae have pale, almost white heads. The black vine weevil is the largest and has a distinct black color. The woods weevil is the smallest of the group.

Hoplia are scarab beetles that are brown and 0.40 inches (10 mm) long. They are primarily a problem in San Joaquin Valley plantations that have not been fumigated. In the San Joaquin Valley, adults emerge in mid-April and are active for about 1 month. They are attracted to strawberry flowers and fruits, where they feed on petals and young, green fruit. Eggs are laid on the soil or on strawberry crowns; the resulting larvae enter the soil to feed on roots and are found associated with the roots from fall through spring. The larvae are 0.45 inches (11 mm) long and characteristically C-shaped. They feed for 2 years before pupating.

DAMAGE

Larvae of all of these beetles feed on the roots of strawberry plants and can completely devour small rootlets and destroy the bark and cortex of larger roots. Soon after feeding begins, plants wilt because the roots can no longer provide moisture for leaves. Hoplia larvae will severely stunt and eventually kill infested plants. It is not uncommon to find beetle larvae that have penetrated into the lower portion of the plant's crown.

Adult weevils feed on foliage and remove large scallops from the leaves. Such leaf damage is a good indication that weevils are present but is not economically damaging to the plants. Adult hoplia beetles feed on flower petals, but it is not known if this injures young fruit.

MANAGEMENT

The rapid removal of plantings following harvest and preplant fumigation destroy beetle larvae and pupae in the soil. Soil solarization may be effective for hoplia beetles in the Central Valley. The use of sudangrass as a cover crop may serve to increase population levels in the field.

Biological Control
Parasitic nematodes that target immature insects in the soil are available commercially. Preliminary research in using them for control of beetle larvae infesting strawberry roots, however, has not proven successful.

Cultural Control
Annual plantings reduce the likelihood of high populations building up in fields. Rotating to a nonhost crop (such as lettuce or cole crops) will further help reduce population levels in the soil.

Organically Acceptable Methods
Cultural controls, especially the use of annual plantings, soil solarization for hoplia beetles, and crop rotation, are acceptable for use on organically certified strawberries.

Monitoring and Treatment Decisions
Even one hoplia grub in the crown or roots will cause significant damage. If plants wilt or appear stunted and/or reddish in color, larvae may be present. Examine roots to determine if root weevil larvae are present, because cold temperatures can also induce reddening. Dig several plants and look for C-shaped grubs in the crown and/or roots.

Soil fumigation for weed and disease control will destroy larvae and pupae in the soil, and root weevils and hoplia beetle do not appear to become problems in fumigated fields. In nonfumigated fields, chemigation can be effective.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
PREPLANT FUMIGATION
A. METHYL BROMIDE*/CHLOROPICRIN* 300–400 lb 48 0
  COMMENTS: Use of methyl bromide for root beetle is not on the current Critical Use List, but there is a use provision if 1,3-dichloropropene products are prohibited because local township limits have been reached. Fumigants such as methyl bromide are a source of volatile organic compounds (VOCs) but are not reactive with other air contaminants that form ozone: methyl bromide depletes ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
 
B. Sequential application of:
  (Note: Fumigants such as 1,3-dichloropropene and metam products are a source of volatile organic compounds (VOCs) but minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.)
  1,3-DICHLOROPROPENE*/CHLOROPICRIN*
  (Telone C35) 9–12 gal (shank) 5 days 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. One gallon of product weighs 11.1 lb.
  . . . or . . .
  1,3-DICHLOROPROPENE*/CHLOROPICRIN*
  (InLine) 28–33 gal (drip) 5 days 0
  COMMENTS: Effective for control of nematodes, soilborne fungal pathogens, and insects. Requires plastic mulch. Using higher rates or plastic mulch, especially virtually impermeable film (VIF), improves weed and nematode control. One gallon of product weighs 11.2 lb.
  . . . or . . .
  1,3-DICHLOROPROPENE*
  (Telone II) 9–12 gal (shank) 5 days 0
  COMMENTS: Liquid that diffuses as a gas through soil. Effective against nematodes and insects. Rates vary with soil texture and efficacy strongly affected by soil moisture and temperature. One gallon of product weighs 10.1 lb.
  . . . or . . .
  CHLOROPICRIN*
  (MetaPicrin) 15–30 gal (shank) 48 0
  (Tri-Clor) 15–21.85 gal (drip) 48 0
  COMMENTS: A liquid that diffuses as a gas through soil. Very effective for control of soilborne fungal pathogens and insects. Drip irrigation requires an emulsifier. For shank fumigation, using higher rates or plastic mulch, especially virtually impermeable film (VIF), improves weed control. For drip fumigation the use of VIF will improve both nematode and weed control. One gallon of Tri-Clor weighs 13.7 lb; one gallon of MetaPicrin weighs 13.8 lb.
 
  Followed 5-7 days later by:
  METAM SODIUM*
  (Vapam HL, Sectagon 42) 37.5–75 gal 48 0
  COMMENTS: Water-soluble liquid that decomposes to a gaseous fumigant (methyl isothiocyanate). Efficacy affected by soil texture, moisture, temperature, and percent organic matter. One gallon of product contains 4.26 lb of metam sodium.
  . . . or . . .
  METAM POTASSIUM*
  (K-Pam HL) 30–60 gal 48 0
  COMMENTS: Water-soluble liquid that decomposes to a gaseous fumigant (methyl isothiocyanate). Efficacy affected by soil texture, moisture, temperature, and percent organic matter. One gallon of product contains 5.8 lb of metam potassium.
 
CHEMIGATION
A. DIAZINON* Label rates 24 5
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Liquid diazinon applied through the drip irrigation system can be fairly effective, and a second application can give almost 100% control.
 
POSTHARVEST
A. CHLORPYRIFOS*
  (Lorsban 4E) 1 qt 24 21
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Apply as a soil drench postharvest in fall for second-year plantings if root weevils or Hoplia beetle infestations have been found. Chlorpyrifos has been found in surface waters at levels that violate federal and state water quality standards. Because runoff into waterways is a concern, apply well before winter rains begin. Do not make more than 2 applications/season.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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.
* Permit required from county agricultural commissioner for purchase or use.
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 are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468

Insects and Mites

  • F. G. Zalom, Entomology, UC Davis
  • M. P. Bolda, UC Cooperative Extension, Santa Cruz County
  • S. K. Dara, UC Cooperative Extension, Santa Barbara County
  • S. Joseph, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to the Insects and Mites:
  • P. A. Phillips, UC IPM Program and UC Cooperative Extension, Ventura County
  • N. C. Toscano, Entomology, UC Riverside

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