Manitoba Agriculture, Food and Rural Initiatives
Root Weevils II
Root weevil
damage to strawberry |
 Root weevil larvae, pupae and adults on soil surface |
 Strawberry root weevil adult |
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Host Plants and Distribution
Root weevils are found in all growing areas in the northern U.S. and Canada, feeding primarily on strawberry and raspberry, but will also attack loganberry, blueberry, grapes, azalea, hemlock, rhododendron, primrose and many other ornamentals.
Biology
Root weevils reproduce asexually and all root weevils are therefore female. These beetles are unable to fly and are active at night. Most root weevils overwinter as larvae near the roots of their host plants. In spring they pupate and adults begin to emerge in early July. Adult weevils are 5-9 mm long and vary in colour from black to light brown to gray in colour, depending upon the species. In late July, the females deposit the eggs near the crown of the host plant. The eggs hatch and the larvae burrow into the soil to feed on the roots for the remainder of the season. Larvae are legless grubs with whitish bodies and brown heads and reach a length of 6 mm. There is one generation per year.
Symptoms and Damage
Feeding damage to leaves (notching) and fruits is minor and not of economic concern but can serve as an indication of weevil presence. Root feeding by the larvae can cause plants to become stunted. Larvae will tunnel into the roots to feed. Leaves may turn red and fruit can be small and seedy. Wilting and plant death can occur during periods of drought.
Scouting Techniques
Scouting should initially be carried out at the margins of fields. As the weevils cannot fly, early infestations will occur at field edges due to adult weevils walking into the field. Infestations spread slowly. Fields should be monitored in July or August for notching in the edges of leaves, which is caused by adult feeding. If notching is observed, return at night with a flashlight to examine the foliage for adult beetles.
Economic Thresholds
Severe infestations in Manitoba are relatively uncommon; therefore, control measures are usually not necessary. No economic thresholds have been established for root weevils.
For further information, contact your GO representative.
