Lawn Weed Management

Rob Witherspoon, Director
Guelph Turfgrass Institute

As of April 22, 2009, Ontarians will no longer have access to traditional herbicides for the control of dandelions and other broadleaf weeds in the lawn. You will need to enhance your lawn care practices and explore alternatives or alter your expectations and learn how to make dandelion wine.

In the spring, your best option is to dig out weeds by hand. You want to remove as much root as possible so hand pulling is not really an option. A number of tools are available for this job. I have experimented with a few of the available models and have yet to find one that is 100% effective at getting all of the root of persistent weeds like dandelion and preventing regrowth. My current strategy is to use a model that removes the weed, about the top 6-8 cm of root and a small cone of soil. I carry a bucket with some good topsoil mixed with grass seed and toss a handful in each of the little holes to prevent other weeds from germinating in the void.


Corn Gluten Meal

There are some options for weed control that will still be available as well as some new options on the horizon. Corn gluten meal has been around for a few years. Normally used as a pet food ingredient, it was found to also prevent seed germination. It has no impact on established weeds but some research has shown that it can prevent new weeds from germinating. Unfortunately, it will also prevent grass seed from germinating so you should avoid using it if you are overseeding your lawn to increase turf density. It is particularly effective in a program to control crabgrass, an annual grass that is a weed in lawns and is starting to germinate right now. For more information about this product, including how and when to apply, follow this link.

Sarritor

Sarritor is a new alternative for broadleaf weed control.  It is a true "biological control agent" in that it is a living organism, in this case a fungus, that selectively attacks dandelions and may also have some activity against other broadleaf weeds. Sarritor is a granular material that needs to be applied directly to the weeds and requires good moisture conditions after application for the fungus to grow and kill the weed. It will not harm grass but will damage other plants so care must be taken to insure the granules do not come into contact with other desirable broadleaf plants like lettuce or petunias. It will not spread through the lawn or garden on its own. Although there are plans to make this product available to homeowners for application on their lawns, it is currently only available from professional lawn care operators and in limited supplies. For more information about Sarritor, check out their website.

Cultural Weed Management

Once you have eradicated undesirable weeds from your lawn, or to keep the weeds you have at a tolerable level, plan a good maintenance program to keep your lawn thick and healthy. A long term demonstration project looking at lawn care alternatives conducted at the Guelph Turfgrass Institute over the last few years showed that fertility was one of the major factors in reducing weed infestation on lawns. The most important aspect from both an agronomic and an environmental perspective is to apply the correct amount of fertilizer at the appropriate time of year. You should ideally fertilize your lawn threes times per year - late spring, late summer/early fall and late fall.  The late fall application is important for winter survival and early but controlled spring green-up and growth.

It has been suggested that repeated vertical mowing can be used to help eliminate or reduce the visual impact of broadleaf weeds in lawns. As the name implies, a vertical mower has vertical blades that rip up the leaves will leaving the grass plants relatively undamaged. Care must be taken to set the mower so that it is not digging deeply into the turf and damaging the crowns of the grass plant but regular vertical mowing may help reduce the appearance and competitive ability of weeds in the lawn. Vertical mowers, sometimes called power rakes or dethatching mowers, are available through equipment rental companies. Many lawn care companies also offer vertical mowing services.

Irrigation is also an important component of managing lawn weeds. If you are in a municipality that restricts summer lawn watering, this may be a bit of a problem but the good news is that lawns will go naturally dormant during a dry summer and weeds don't do so well either. However, regular irrigation will help enhance the ability of the lawn to out compete weeds. The key is to water deep and infrequently. The worse thing you can do is water every day or every other day as the soil surface will remain damp which provides ideal conditions for weed germination. Err on the side of keeping the lawn drier as opposed to wetter to prevent weed seed germination. With proper irrigation, good mowing practices (a sharp blade, mow high and return the clippings to the lawn), periodic aerating to manage thatch and overseeding as needed to increase turf density, it is not that difficult to have a reasonable lawn in the absence of pesticides. Insect problems are going to be the greatest challenge of managing pesticide free landscapes. Keeping the lawn thick and healthy will help as will quickly overseeding any damaged areas. Hopefully the elimination of pesticide use will help stimulate investment in research to develop effective alternatives so we can still enjoy the environmental, recreational and aesthetic value of our lawns.