HPIPM:Mint Strawberry Root Weevils

Author: Sue Blodgett & Bill Grey

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Cucujiformia
Superfamily	Curculionoidea
Family	Curculionidae
Subfamily	Entiminae
Tribe	Otiorhynchini
Genus	Otiorhynchus

Scientific Name

Otiorhynchus ovatus

Scientific Name Synonyms

Brachyrhinus ovatus

Common Name

strawberry root weevil

Identification (life cycle and seasonal history)

The strawberry root weevil (SRW) is the primary species in the root weevil complex attacking mint that includes the black vine, rough strawberry and obscure root weevil. Most root weevils overwinter as larvae in the soil, but a few adult weevils also overwinter in protected areas. Overwintering larvae mature during the end of April and early May and form earthen cells in the soil where they pupate. Adults begin emerging in early summer and are usually present in mint fields through late September. All SRW are females, capable of laying eggs without fertilization. Eggs are deposited around the bases of plants about 2 weeks after adult emergence. There is one generation each year.

Natural spread of root weevil infestations in and among fields is gradual because adults do not fly. Serious infestations can, originate when roots and rhizomes are dug from infested fields and introduced into non-infested areas.

Plant Response and Damage

The damaging larval stage begins feeding on small mint roots very soon after emerging from the eggs. Larvae feed through the summer and early fall, at which time they reduce activity until the following spring when feeding is resumed. Adult damage, which may be evident during summer months, consists of small notches on the leaf margins and stems, particularly near the soil line. Adult feeding on mint is usually inconspicuous and is not economically important. Adults are active at night resting during the day in plant debris.

Management Approaches

Degree day units (DDU) may be used to predict the occurrence of the different life stages of strawberry root weevil using a base temperature threshold of 48oF beginning January 1. Pupae are present in samples from late April to early June (350 DD) with peak pupation occurring in early summer. Peak adult emergence occurs in mid-summer (700 DD).

Larvae are best estimated by taking 1000 cm2 soil samples after harvest or the following spring. Take at least 25 soil samples from different areas of the field (one site per 2 1/2 acres), screen the soil, count the number of larvae and calculate the average number per sample. If the average number of root weevil larvae exceeds 5 – 8 larvae per square foot, suggests need for control.

Adults are sampled by taking 10 sweeps in at least 5 field locations (for a 30A field). Best times to sweep for SRW is a couple hours after sunset on a warm, still and dry evening. When 5 or more adults are collected in 10 sweep sample, treatment is warranted.

Cultural Control

Natural spread of root weevil infestations in and among fields is gradual because adults do not fly. Purchasing certified pest free rootstock can eliminate the introduction of this pest into new plantings.

Chemical Control

Spring applications to control strawberry root weevil have met with limited success largely because of low soil temperatures (< 60oF).

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.