Weevils on my Pinky Winky hydrangea

(Question)

This is the second season for my hydrangea and my weevil problem.  My husband has been vigilant about weevil hunting at night.  Last year we were advised to wrap the lower part of the branches with double sided sticky tape….

Is there anything more that you can suggest that we can try?  We can’t seem to find a successful weevil erradicator!

(Answer)

What you most likely have is an infestation of Vine Weevil, Otiorhynchus sulcatus.

To choose control methods that are best for your garden, an understanding of the insect life cycle is important.  Weevils lay their eggs in soil in autumn, which turn into larvae and feed on plant roots during the winter.  In the spring, adults emerge and over the summer feed on plant foliage.  Therefore, the damage to a plant is two fold and can be detrimental.  This can be a problem in an open garden or container setting.

Cultural control measures include:  picking off individual insects by hand in the late evening using a dim flashlight for illumination, shaking your shrub over an upturned umbrella or plastic ground sheet in order to catch & destroy insects, placing sticky barriers around the base of the plant in order to stop adults from climbing up, or finally, encouraging natural weevil predators such as birds, frogs, hedgehogs or ground beetles into your garden.  These cultural practices address only the adult weevil.  It is also a good idea to remove all plant debris such as leaves etc… from around your plant and to monitor other plants in your garden for any weevil spread.

Biological control measures target the insect while it is in the soil at the larvae or grub stage in its life cycle.  There are two nematode genera ( Steinernematidae and Heterorhabditidae) that can be used and both are commercially available.  Of note, each has a specific application soil temperature when it is most effective.  Steinernematidae is best when soil temperature is 5-20 degrees C, and Heterorhabditidae is best when soil temperature is 12-20 degrees C.  For both, application is done in August or early September, when the soil is moist (after rain or a good sprinkling), on an overcast day and onto soil that is rich in organic matter.  Follow storage instructions (refrigeration) and application instructions on the container very carefully and use the correct amount of solution for the garden area.  More than one application may be needed to target earlier or later emerging larvae.

There are no Chemical control options available for use in an open home garden.

To combat your infestation, a combination of Biological and Cultural control practices is advised and it may take a couple of growing seasons before you feel that the problem is manageable.  Good luck.