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Viburnum Beetle & Global Warming

It’s almost time for attacks from Viburnum beetles; and Scientists, including from Canada, are calling for action to slow down global warming!
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

February 13, 2005

Above: two photos of the Viburnum leaf beetle, courtesy of the University of Massachusetts, photos by R. Childs; and below, two photos of windmill farms in the Palm Springs area of California. We will likely be seeing many more of these in the future. Author photos.

Late this week Sue Hopwood of Lakehill (Victoria, B.C. I think) wrote as follows: “Donna Dawson suggested I write you about my problem--so here goes. Two years ago my Viburnum (Snowball) shrub started getting chewed and the chewed leaved looked like brown lace. Last year I was ready for it and at the first sign of a hole I sprayed well with BTK. It didn't help at all. By the end of the summer the poor thing was in brown lacy tatters. It had kept pushing new growth but this was also chewed up. Also, my Viburnum bodnantense was starting to have the same problem by the end of summer.

I think I heard Ken Beatty talk about a Viburnum Weevil on his show but I'm not sure that is the right name. Have you heard of this problem and do you have any suggestions? I do have some Isotox left over from before the ban. Would it help to use this? Thanks for any help you can offer.”

Well, yes I certainly have dealt with this pest for years. It is more correctly known as the Viburnum beetle or Viburnum leaf beetle (Pyrrhalta viburni). Oddly enough, it is closely related to the Elm leaf beetle (Pyrrhalta luteola) which causes the foliage of numerous elm trees to turn brown and the entire trees to appear ugly. How-ever, it is not to be confused with the infamous Elm bark beetle (Hylurgopinus rufipes) that is the vector of the horrendous Dutch elm disease.

The Viburnum beetle actually has a double whammy effect on various Viburnum in that the larvae hatch from eggs laid (on the young twigs the previous late summer) usually in early May (possibly even earlier in mild zones in British Columbia) and begin skeletonizing the foliage. By June, they begin to fall to the ground and pupate in the soil beneath. Then in late July, the adults emerge to begin feeding on the already badly damaged foliage. In late summer, the adults lay eggs in small, young twigs. They place a couple of eggs in each hole, generally on the underside of the twigs, and usually the holes are in a straight line on the twig. The holes are ‘filled’ with a chewed wood but are reasonably obvious. That is the first line of defence! Check for the telltale signs of the lines of tiny holes on the underside of twigs in late March or early April. If you see these, cut off those twigs and burn them.

As to treatment to kill the larvae, the best time is in late May and early June, using a couple of applications. Any good insecticide will work, but the time of application is critical. Yes, your old Isotox will work, but if you have to purchase something, I would get a can of the yellow-labelled Doktor Doom Residual Insecticide Spray (check for garden centres carrying the product).

I have on several occasions seen beautiful Viburnum shrubs killed by successive (three or more) years of attack by the Viburnum beetle and its larvae.

According to a report published in the February 3/05 online edition of Nature magazine, "Major investment is needed to help people mitigate and adapt to global warming. So say the 200 top climate scientists, and a hand-ful of economists and politicians, assembled this week at Britain's Met Office. It is clear that the risks of cli-mate change are more serious than was thought a few years ago, the scientists say.

“Avoiding Dangerous Climate Change, a meeting organized by the UK government and the Exeter, England-based Met Office, attempted to assess the current and future state of climate change, and how to avert it.

“Many concluded that it is impossible to define "dangerous" climate change, as impacts vary wildly from place to place. Regardless, others hoped that one message would be clear. ‘We don't really need more detail now,’ says Michael Mastrandrea from Stanford University, California. ‘We already have enough information to make an educated guess on how we need to reduce emissions.’

“Researchers agreed that the predictions about climate change made a decade ago are coming true. ‘Thermal expansion of the oceans, acidification of water, increased air temperature leading to more storms; there is evidence for all this now,’ said Larry Hughes, an environmental researcher from Dalhousie University in Halifax.

“And it is apparent that things aren't getting better, says Robert Socolow, co-director of the Carbon Mitigation Initiative at Princeton University in New Jersey. ‘What we can tell politicians is that the list of worries is going to grow.’

“The Antarctic is one key area of concern, says Chris Rapley, director of the Cambridge, England-based British Antarctic Survey. Five years ago, he and most scientists were not concerned about Antarctica melting, he says. But recent evidence shows that the Pine Island Glacier is eroding, and might unleash a mass of ice from the western half of the continent.

“If western Antarctica melts, it will raise sea levels by about 6 metres, Chris Rapley says. ‘We don't know what will happen. But we know we should be studying it,’ he says. Others presented worries that were more familiar, but just as real: Greenland may melt; Africa may experience more drought; acidic oceans will imperil coral reefs; and ocean circulation in the Atlantic may shut down, freezing northern Europe.

“Several noted that we have the technology to prevent serious temperature rises, at the relatively moderate expense of four percent or less of the world's GDP (gross domestic product). The options include better energy efficiency, or capturing carbon dioxide as it is produced from power plants and burying it underground.

“David King, the UK government's chief scientist, said during the meeting that he had spoken to oil companies about the possibility of pumping carbon dioxide into old oil wells in the North Sea.

“Making the cut Robert Socolow summarized what could be done. For carbon emissions to remain stable over the next 50 years, he said, we would need to reduce projected emissions in 2054 by 7 billion tonnes of carbon. One billion tonnes of cuts could be achieved by doubling the fuel efficiency of two billion cars, or by building two million one-megawatt electric windmills, or even by doubling the electricity produced in nuclear power plants.

“All of these numbers carry a large amount of error. And scientists said that it was hard to work out what the atmospheric concentration of carbon dioxide would have to be to lead to a 2° C warming on pre-industrial times. This is the figure that the UK Prime Minister, Tony Blair, had asked them to provide.

"Science cannot come up with a single threshold. That's what politicians are for," says Malte Meinshausen of the Swiss Federal Institute of Technology in Zurich.”

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