McGill University, Faculty of Agricultural and Environmental Sciences

Bad News for Dandelions

excerpt McGill Reporter April 11, 2002 - Volume 34 Number 14
by Bronwyn Chester

Pretty as they are when they first bloom and tasty as their young leaves may be, outside of children and salad-lovers, dandelions have few defenders. Highly successful thanks to its seeds being handily transported when the wind picks up the downy tufts, Taraxacum officinale, is the scourge of lawn-growers, golf-course keepers and anyone trying to maintain a grass playing field.

No long ago, you could spray the tenacious broadleafed weed and that was that. But many municipalities, pressured by citizens concerned with the health effects of such chemicals as 2,4-D and Killex, have outlawed chemical control.

All of which makes Alan Watson's fungal inoculate for the biological control of dandelions, Sclerotinia minor, very attractive. Watson, a professor of plant science, has already made headlines with the fungal pathogen he isolated to control the insidious African witchweed, Striga hermonthica, which constrains cereal production. He may soon do the same here once Sclerotinia has been registered with Health Canada and the Environmental Protection Agency, in the United States.

Watson and his co-workers isolated the dandelion's fungal pathogen in 1988, having found that a common lettuce fungus worked just as effectively on the tenacious yellow flower, as well as on such spiny weeds as the bull thistle. Since then, he's been able to perfect the technique of production using autoclaved (sterilized) grains of barley in which the fungus takes five to seven days to colonize. Then the small grains, resembling cracked wheat, are packaged.

Only a tenth of a gram is needed to kill the dandelion and the grain may simply be dropped onto the plant. Getting it to stick there is another matter. "We may need to make the granules stickier, perhaps with a gelatin powder that would react with the moisture in the leaves," says Watson, adding that the granules work best in a cool temperature and are best applied in the early fall and spring.

The advantage of using a fungal inoculate over using a chemical is that no harm is done to the surrounding environment, including any birds who may swipe a granule of inoculated barley. In theory, other broadleafed plants, like tomatoes and lettuce, are at risk of being killed by the fungus if contaminated. The danger lies in a granule straying from the target plant and with the sclerocia, the dormant and stationary stage of the fungus, staying in the ground and becoming activated once in contact with any broadleafed plant.

"You don't want it staying long, living in the environment. We're working on fail-safe systems so it won't produce sclerocia," says Watson.

So far, the results have been good. In an "overwintering" trial, when lettuce was planted on the site where a dandelion had succumbed to the fungal product, the lettuce was unaffected.

Does this mean, then, that we'll soon see the granules for sale at the local Canadian Tire? Watson says that depends on how long it takes to get the substance registered. He is, however, setting up a spin-off company and he's optimistic for himself and the University that there will be a market.

"2,4-D is very inexpensive so it will be hard to compete, but our advantage is that this is non-chemical and there's a push from the public for non-chemical solutions to weeds," he notes.

In case the development of this dandelion inoculate for largely cosmetic reasons leaves you scratching your head, be reassured that this same Sclerotinia will also have a future in cereal crops, such as wheat, oats, barley and corn. These crops didn't used to be affected by the dandelion. But now that "no-tillage" systems -- because not tilling conserves fuel and keeps more nutrients in the soil -- are becoming more popular, new weeds are appearing.

"Dandelions are now a big problem in no-till corn," says Watson. "So there will be an application of this product in agriculture too."