Viburnum beetle

What is viburnum beetle?

Viburnum beetle is a defoliating pest of some Viburnum species. Most of the damage is caused by the larvae in late spring but some further feeding damage is done by the adult beetles in late summer.

Heavy attacks can result in most of the foliage being severely damaged in late spring. Damaged leaves are discoloured with brown dried up edges to the holes created by the adult beetles and larvae, especially on Viburnum tinus. This shrub often produces an unpleasant smell when the damaged foliage becomes wet.

Symptoms

An attack of viburnum beetle results in:

• Holes eaten in the leaves, with the larger leaf veins remaining, giving the foliage a lace-doily appearance
• Creamy yellow larvae, with black markings and up to 8mm long, are present on plants in April to early June
• Greyish brown adult beetles, 4.5-6mm long, feed on the leaves from late July to September

Control

Non-chemical control

Larvae are normally too numerous to hand pick so attacks may have to be tolerated.

Chemical control

Inspect susceptible viburnums during the spring for signs of feeding on the new foliage. This will indicate when the overwintered eggs are hatching. If necessary, spray the plants with deltamethrin (Bayer Sprayday Greenfly Killer), lambda-cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer) or thiacloprid (Bayer Provado Ultimate Bug Killer). Organic gardeners can use pyrethrum (eg Py Spray Garden Insect Killer, Doff All in One Bug Spray, Scotts Bug Clear Gun for Fruit & Veg). Pyrethrum should control newly hatched larvae but will be less successful against the adult beetles.

The best time to spray is when the newly hatched larvae are feeding on the new foliage in mid-April to early May. Treatment in mid-summer is really too late as the worst of the damage has already been done.

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

Viburnum beetle overwinters as eggs that are deposited in the bark of the stems in late summer. These eggs hatch in late April-early May and the larvae begin feeding on the new foliage. When fully fed in late May-June, the larvae go into the soil to pupate. Adult beetles emerge in late summer and after mating, deposit batches of overwintering eggs in the woody stems.
 

Most of the damage is caused by the larvae during late spring. Adult feeding damage on the foliage is much less extensive than that of the larvae.