Spring Broadleaf Weed Control in Virginia’s Lawns
Warm spring temperatures lead to a resurgence in growth from our lawns as well as our broadleaf weeds. What steps can we take to maximize weed control while protecting our turf and our environment? This podcast details best management practices in spring broadleaf weed control.
Cool-season lawns featuring bluegrasses, fescues, and ryegrasses will soon be rapidly growing now that spring has arrived and warm-season grasses like bermudagrass, zoysiagrass, St. Augustinegrass, and centipedegrass will be aggressively emerging from their winter slumber very soon as well. It is not just our turfgrasses that are resuming a surge in growth. Most broadleaf weeds in our lawns are equally responsive to warmer temperatures and longer days too. Spring affords an opportunity to gain control of these weeds, but there are some best management practices (BMPs) and precautions that we can apply to deliver the desired result and protect our environment.
First of all—what do you consider to be a weed? A weed is simply defined as a plant out of place; any plant you deem undesirable in your lawn therefore can be classified as a weed. Weeds typically possess the capacity to grow rapidly, spread to new territory, and persist through difficult environmental periods. They have some niche which allows them to successfully compete with turf: maybe they are better adapted to poorly drained soils, compacted soil conditions, shade conditions -- do you see a pattern here? Anything that limits turf growth sets the stage for weed invasion. Virginia Tech’s Extension Turfgrass Weed Specialist, Dr. Shawn Askew, always reminds us that the absolute BEST weed control in the lawn IS the lawn. The ideal way to keep weeds at bay is to manage your lawn appropriately re: fertilization, mowing, aeration, irrigation, and so forth.
One of the biggest reasons weeds are deemed unacceptable is they disrupt lawn uniformity. Their shape, color, height, and/or growth habit causes them to stand out, and while such diversity in shape, color, etc. is often expected (sometimes demanded) in our ornamental beds, it is standard practice to try to maintain uniformity in turf. However, your expectations for what constitutes an acceptable lawn can vary a great deal from your neighbors. In the early years of managed turf, white clover was considered to be an integral component of the lawn because of its ability to fix N as a legume. To this day, there are seed mixes for lawns featuring grass and clover. There is much to be said for such "natural" lawns, but everyone has a different perspective on the value and function of a lawn. One of the biggest challenges in "natural" lawns is that there is usually very little ability to selectively manage mixed stands of grass and broadleafs. An extremely aggressive weed such as dandelion in a mixed clover/turfgrass lawn can essentially not be controlled with selective broadleaf chemistry. Perhaps you even admire the bright yellow blooms of the dandelion flower, but there is probably somebody just down the street cursing you under their breath when the seed from your dandelions become airborne in the very near future and start to drift into their lawn. These neighborhood "battles" (between the weeds AND the neighbors!) take place throughout the spring and summer. If you choose to enter the fray and combat weeds with a chemical approach, then be sure you target the weeds in a responsible manner.
Spring is a great time for broadleaf weed control as temperatures warm consistently into the 60s and 70s and the plants really begin to grow. But before you make a chemical application, do some homework to understand just what it is in your lawn that you are targeting with a chemical application. What weed(s) are present? And perhaps as much important as what they are is knowing about their life cycle: are they annual (complete their life cycle within one growing season) or perennial (persist for 2 or more years) broadleaf weeds? Winter annual broadleaf weeds (things such as henbit, deadnettle, chickweed, sibara, bittercress, and geranium) flower prolifically in the spring (I’ve even had recent requests on where one can buy seed for deadnettle because the homeowners just love those bright pink/purple flowers!), and their color is attracting a lot of attention (most of it unwanted… the homeowners above tend to be the exception!). However, is it appropriate to target these annual plants with a herbicide when they are in bloom? The answer is maybe, but if you are truly trying to take a BMP approach, the best answer would be you should have controlled them earlier in the season before they flower and set seed. Remember, they are winter annuals; they germinate in early fall and will die in mid-late spring when temperatures warm. As they flower and set seed, their life cycle is completed. They are very mature at this stage in their life and do not absorb as much herbicide as when they are young (that is, they are more difficult to control now). About the best you can do now is accelerate their inevitable death by a few weeks. Make a note to change your control strategy for future years by targeting their control when they are young and actively growing during the fall or warm winter periods.
On the other hand, if you are going after perennial broadleaf weeds (things such as dandelion, clover, and plantains) then this is an outstanding time to treat for these plants. Rapid growth rates of the weeds usually equates to better chemical absorption of the herbicide and better control. There are some precautions, however. For both cool and warm-season grasses, if you are using a weed and feed product, try to find materials that contain significant percentages of water insoluble (i.e. slow-release) Nitrogen that will slowly feed the turf. Excessive rates of N in the spring potentially lead to more summer stress from environmental and pest extremes. And likely of even more concern is the choice of herbicide, especially on transitioning warm-season turfgrasses. Make sure your product says it is specifically targeting broadleaf weeds and then check to see exactly what chemical(s) it contains. One of our major components in combination broadleaf weed control products, 2,4-D, can particularly damage warm-season grasses during spring transition from dormant to actively growing turf . It is wise to select products that specifically detail their use on warm-season grasses for many broadleaf herbicides, so take a little extra time to read the label regarding precautions and appropriate uses. Lawn care operators have access to specialty products not labeled for homeowner use, so employing their expertise is always an option in weed control that is worth exploring. (Remember—the pesticide label is the LAW—follow all directions to provide the pest control you desire AND to protect you, others, the environment!).
One of the assumptions here is that you have identified the weed species in your lawn to know whether it is an annual or perennial. You probably know dandelion, clover, and deadnettle when you see it, but there are thousands of weedy possibilities out there – where can you turn for help in ID? There are several excellent resources available through Virginia Cooperative Extension and Virginia Tech. One is the website specifically designed for Weed ID. Check it out at http://ipm.ppws.vt.edu/weedindex.htm. Another that is full of several thousand images of some of Virginia’s most prolific turfgrass weeds is Dr. Askew’s TurfWeeds website (www.TurfWeeds.net). You can also get the information and steps to follow in submitting actual weed samples to VT’s experts for weed identification services at http://www.ppws.vt.edu/~clinic/weedid.html. Many of these sites also feature links or detailed listings on other weed ID resources and books from around the country.
Please check out the other "spring specific" VCE publications that are linked through our Turf and Garden Tips website. Remember that your local Virginia Cooperative Extension office is ready to assist you with your lawn and landscape questions.