In terms of expense and labor, of all the inputs or maintenance activities required, a strong case can be made for weed control as the greatest. Soil scientists estimate that, on average, between 10,000 and 40,000 weed seeds are present in a cubic foot of soil. Also, compared to other pests, such as fungus diseases and insects, weeds tend to have a greater window for possible invasion into the landscape. While certain temperature and moisture conditions can favor the development of specific weeds, they are much less dependent on weather and other environmental factors than insects and diseases.

Weed ID

When embarking on a weed control plan, it’s important to begin with identifying the species that are most troublesome on the properties you manage. Many resources are available for assistance. Purdue University sponsors a Web site that guides turf and landscape managers through the identification of an unknown weed. If this step is skipped, or the weed in question is misidentified, lots of time and money will be spent for nothing.

Weed mapping of properties

Consider weed mapping, which is simple documentation of previous weed infestations, on the properties you manage. Weed mapping facilitates the opportunity to focus herbicide applications on “hot spots” instead of blanketing the entire turf or ornamental bed. This reduces expended money and labor for each account. In addition, it provides the possibility to offer a more sustainable approach to your clients, where only the weeds that exist, or are likely to exist, are sprayed.

Begin by obtaining a simple plat or survey plan of the property and photocopy it. Make oval, circular or rectangular shapes on the paper to indicate where troublesome weeds have grown. Use colored pencils to indicate different weed problems, such as purple for purslane in the ornamental beds or foxtail and crabgrass in the front yard turf.

PHOTOS BY ROCH E. GAUSSOIN, UNL.
Herbicides offer the flexibility and efficiency to minimize weed encroachment. The herbicide-treated plot is to the right.

Timing

Timing is crucial to effective weed control in the landscape. Each weed, or group of weeds, has an optimal timing associated with it. The key is to identify the most vulnerable stage in the life cycle of the plant and take the appropriate action. Fall is best for broadleaf perennials, and is also a good time to consider applications for annual weeds, depending on the history of the site.

Here’s why:

  1. There is less cuticle on the leaf surfaces. A thick cuticle usually lessens herbicide effectiveness, functioning to reduce foliar absorption.
  2. There is less chance of spray drift injuring vegetable plantings in nearby gardens. For the most part, the vegetable season is winding down.
  3. Perennial weeds store carbohydrates and sugars in the fall, and are likely to translocate the herbicide to the roots, crowns and stolons; for perennials, this is an important development.
  4. If the weed doesn’t die outright from the application, it will be weakened and less likely to survive the winter.

Improving effectiveness

Several strategies can be utilized to increase the effectiveness of each herbicide application:

  • Mowing before and after the application—A certain amount of surface area is required for herbicides to be absorbed by the leaves. If an application is made the day after mowing, there may not be enough leaf area to allow enough product to enter the leaves. Likewise, if an application is made the day of or day before mowing, there may not be enough time to allow for absorption before the surface area is reduced. Endeavor to time applications halfway between mowing cycles.
  • Use of surfactants—Surfactants lower the surface tension of the spray tank water, serving to create flatter herbicide droplets that cover a greater portion of the leaf than if it were not used. Greater leaf coverage can result in greater effectiveness. However, check the contents of the product; it may already have a surfactant in it.
  • Spray on low-wind days—The ideal spray application scenario is one with no wind. Monitor the ambient wind speed before each application: if it is 5 mph or less, spray conditions are good; if it is between 5 and 10 mph, proceed with caution; if above 10 mph, don’t apply a liquid herbicide.
  • Should you water-in the application? The best source for this information is the pesticide label, however, it depends. Generally, for liquid products, no; generally, for granular products, yes. Irrigation or rain events that occur after a liquid application usually dilute the effect of the herbicide and should be avoided, as the goal is to keep the product on the leaf for two or three days. Conversely, the goal is to move herbicide granules off the leaf surface and into the soil. This is most common with preemergent applications for ornamental gardens and lawns. Yet, if the product is intended to control broadleaf weeds (such as a “weed-and-feed” product), it too must stay on the leaf surface, and irrigation water would greatly reduce effectiveness.

Product update

Advances in herbicide technology have resulted in the availability of new chemistries with reduced toxicity to nontarget species and increased effectiveness, new formulations and creative new combination products for the turfgrass professional.

  • Dismiss (www.fmcprosolutions.com/LawnCare/Products/Herbicides/Dismissturfherbicide/tabid/1287/Default.aspx)—In addition to pre and post-activity on yellow nutsedge, Dismiss is effective on a multitude of broadleaf weeds and, while the testing was not done in New England, also has good activity on goosegrass. Weeds susceptible to Dismiss show injury relatively quickly, often within 12 to 24 hours.
  • SpeedZone, PowerZone, Surge and Q4 (www.pbigordon.com/professional/herbicides.php)—SpeedZone has been referred to as “Trimec with an attitude.” The “attitude” comes from the addition of carfentrazone to the industry-standard Trimec components, which results in faster activity on susceptible species. PowerZone is a non-2,4-D alternative to SpeedZone for use in areas where 2,4-D is not desired. Surge contains the components of Trimec with the addition of sulfentrazone, and is formulated to be used safely later in the season. The sulfentrazone will suppress yellow nutsedge. Q4 is the components of Surge with the addition of quinchlorac, increasing the spectrum to include many annual grassy weeds.
  • Certainty and RoundUp PROMAX (www.monsanto.com/ito/layout/turf/certainty.asp, www.rounduppromax.com/?&level1=TurfAndOrnamentalProducts&level2=TurfProductsOverview)—Certainty is safe on warm-season grasses, Kentucky bluegrass and creeping bentgrass. It is an excellent yellow nutsedge product and will selectively remove rough bluegrass, tall fescue and quackgrass from Kentucky bluegrass. For those wishing to maintain pure stands of Kentucky bluegrass, Certainty offers selectivity for difficult-to-control perennial grasses. RoundUp PROMAX offers the security and confidence of the industry-standard nonselective herbicide glyphosate in a more concentrated formulation and smaller packaging, decreasing storage and shipping requirements.
  • Onetime and Drive XL8 (www.betterturf.com/New_News/13/3008.htm, www.betterturf.com/folders.asp?uid=2908)—Onetime is a new combination product containing dicamba, MCPP and quinchlorac that offers broad-spectrum broadleaf and annual grass weed control. Tests have shown good to excellent activity on ground ivy and dandelion and, as expected, clover, crabgrass and foxtail. Drive XLR8 is an improved formulation of Drive (quinchlorac) with quicker response and rainfastness in less than one hour.
  • Tenacity (www.greencastonline.com/TenacityHerbicide/index.html)—Tenacity is a new herbicide registered in 2008 for golf courses and sod farms and federally registered for commercial applicator residential use in 2009. State registrations for residential use are pending. It is safe on cool-season grasses when used as directed, and trials have shown good to excellent control of creeping bentgrass, nimblewill and windmillgrass in Kentucky bluegrass, and good to excellent control of a laundry list of broadleaf weeds, crabgrass and foxtail. Another unique property of Tenacity is safety at seeding. We have testing applications at planting for safety on Kentucky bluegrass, perennial ryegrass and tall fescue with excellent results.
New chemistries in herbicides offer control of difficult weeds like ground ivy with reduced toxicity to nontarget species.

Note: The mention of product names does not constitute an endorsement by the authors, the University of Nebraska-Lincoln or the publication, or a non-endorsement of products not mentioned.

John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln. Roch Gaussoin is a professor of horticulture and extension turf specialist at the University of Nebraska-Lincoln.