Adult vine weevils are flightless beetles with a short snout and a pair of elbowed antennae. They are dark brown or black in colour, with fine yellow speckles, making them appear dusty. These nocturnal beetles feed on the edges of leaves during April to August, causing notching in the foliage; they then hide during the day at the base of plants, under plant pots or in debris. Although they are flightless, they can walk and climb very well, which can make plants in hanging baskets and wall boxes an easy target.

All vine weevils are female, and each adult beetle is capable of laying 500-600 eggs throughout the summer. The eggs develop into extremely destructive creamy-white larvae that feed on plant roots, causing the plant to grow slowly, wilt, collapse and die. The grubs then over-winter in the soil before pupating and hatching into adult beetles in the spring.

Control

To control vine weevils, it is essential to maintain excellent greenhouse hygiene to reduce the number of hiding places for the adult beetles.

Young larvae may be controlled by using a drench of HCH or pirimiphos-methyl in mid-summer, and again one month later. Unfortunately, older larvae are tolerant of all pesticides available to the amateur gardener. They may, however, be controlled biologically by using their natural enemy, the parasitic nematode, Steinernema kraussei, applied as a drench. The nematode is best applied in the spring (March-May) and the autumn (late August-November), as this is when the highest numbers of vine weevil grubs will be present in the soil. Although this is an effective treatment for vine weevil larvae, it will have no effect on the adults or eggs.