Grubs May Be Causing Excess Dandelion Growth

WOOSTER, Ohio - If you see your clients' lawns turn bright yellow with dandelions, the real problem may lie below, not above the ground.

An Ohio State University study has found that root feeding by Japanese beetle larvae on turfgrasses makes it easier for dandelions to become established and multiply in the lawn. And it makes it harder for you to get rid of the weeds.

“Insect management and weed management are more closely linked than previously thought, and our research shows that connection,” says Doug Richmond, a postdoctoral researcher and applied ecologist with the Department of Entomology on the Ohio Agricultural Research and Development Center’s (OARDC) Wooster campus. “Instead of looking at insects, diseases and weeds separately, we need to look at the system as a whole. We need to understand that what we do to manage insects, for example, may have an impact on weeds.”

With OARDC colleagues Parwinder Grewal, an entomologist and turfgrass scientist, and John Cardina, a weed scientist, Richmond studied the influence of Japanese beetle larvae on performance and competition between dandelion and two species of turfgrass, perennial ryegrass and tall fescue.

The scientists found that the grubs, which feed between mid-summer and late fall and again in the spring, consistently reduced the number of tillers and above- and below-ground biomass of both grasses. And if this damage weren’t enough, grub feeding also helped dandelions produce more leaves and greater biomass.

“The grubs don’t attack the dandelions, in part because of defensive compounds these weeds have in their roots,” Richmond points out. “As a result, dandelions have a competitive advantage in their interaction with turfgrass.”

This connection between grub damage and weed growth can have important implications for lawn care.

“In this case, the weeds are only a symptom of the real problem, which is the grubs,” Richmond says. “You can apply herbicides trying to treat the weeds, but you won’t be successful until you take care of the actual cause.”

Although below-ground feeding by insects may be more damaging than above-ground feeding, few studies have taken a look at its effects on the development of grasses. And even fewer studies have detailed the influence of root-munching pests on the way grasses and weeds interact.

“It’s been an assumption that anything that affects grass, such as insects, decreases its ability to fight other competitors, such as weeds,” Richmond explains. “But there’s not a lot of data on this. Little has been done as far as taking an ecological approach to studying turfgrass systems. Lawns are ecosystems with a lot of interacting pieces, just like a forest, and should be thought of as such.”

Therefore, proper insect control should be an important part of weed management for turfgrasses, he says.

OARDC is the research arm of Ohio State’s College of Food, Agricultural, and Environmental Sciences. For more information, contact Espinoza at espinoza.15@osu.edu or 330/202-3550.