Know Your Enemy

  • By simple definition, a weed is a plant out of place. Typically, a weed finds a bare or thin area within the desirable plants and spreads by growing more aggressively than they do. The right turfgrass in the right spot will ward off many weed issues. Thick, healthy turfgrass is your best defense.
  • Weed identification is essential, whether the invader is a broadleaf, grass or grass-like plant, such as nutsedge. A weed may be an annual or perennial, and propagated by multiple means: migrating seeds; tillers and/or rhizomes; or sprigs brought in by cleats, mowers or other maintenance equipment.
  • Each weed species is genetically programmed to require a specific range of soil conditions and to respond to a combination of light, temperature and moisture factors that trigger its growth cycle. Knowing this information about a weed, you often can adjust your cultural practices to make your fields less habitable for it.
  • Turfgrass extension specialists are excellent resources for region-specific information. Most maintain data-filled websites. Some have blog posts and email messaging for pertinent updates. Check out the mobile apps available through state turfgrass extension departments and weed control product suppliers. Load one on your smartphone or tablet to access those basics in the field.

Best Management Practices (BMP)

  • BMP is like Integrated Pest Management (IPM) on steroids. It starts with all the principles of IPM: identification, tracking, establishing an action level for each pest, and ranking control options from the least to most aggressive, starting with cultural practices, moving to organic and then nonorganic applications. BPM adds the sustainability aspect, considering the current and long-term environmental impact of any action in terms of people, pets and wildlife, insects (including pollinator protection), other plants, water and soil.

Each weed species is genetically programmed to require a specific range of soil conditions and to respond to a combination of light, temperature and moisture factors that trigger its growth cycle.

Pinpoint the Location

  • If you’ve not already done so, develop an accurate map of the fields and landscape areas you manage. Then determine and plot out the precise location for each weed infestation. (You’ll use this same map to pinpoint insect and disease problems.)

Track the Weather

  • Many extension websites offer weather tracking, posting degree-day data you can use to help determine key points in a weed’s life cycle, such as the potential germination date. View your state’s data and that of the states along the path of your typical weather patterns to anticipate when control applications may be needed.
  • Moisture and temperature both impact the timing and effectiveness of herbicide applications. Put a couple weather apps on your computer and smartphone. Compare the data between those apps and the local radio and television meteorologists, tracking the forecasts for accuracy, so when weather systems move in quickly you’ll know which to monitor.

Application Options

Poa annua shows up as light colored patches in this mixed bluegrass/ryegrass field.

  • Herbicides may be nonselective, acting on every green plant they contact; or selective, only acting directly on a specific range of plants. They may be classified as preemergence products (preventing weed germination and development) or as postemergence products (acting on an existing weed). Some products combine preemergence and postemergence control. Postemergence herbicides may be contact products (acting on the plant surfaces they touch) or systemic (absorbed by the plant and moved throughout the plant structure).
  • New products are continually being introduced and existing products refined. Before making a product decision, consult with your suppliers, turfgrass extension personnel and networking contacts to determine the most effective choice for your specific situation. Abide by all restrictions on herbicide use by national, state and local governmental agencies and your facility’s ownership.
  • Determine the area to be treated based on the following: degree of weed infestation; location of the weeds; stage of weed growth; condition and growth stage of the desired turfgrass; and the timing of any anticipated reseeding or overseeding. Field use schedules must be considered along with post-application entry restrictions.
  • Proper timing is essential for preemergence applications to ensure an effective level of active ingredient is in place to block weed growth. Postemergence herbicides generally are most effective on younger weeds. But there are exceptions, such as end-of-season application on perennial broadleaf weeds in cool-season turfgrasses. BMP may dictate spot treatment or limited-area application over full-field application.
  • The product label will list the following: active ingredients; weeds it impacts; its mode of action; turfgrasses it can be used on; recommended rates of use; recommended timing and frequency of applications; any required precautions; and any potential impact on desirable plants. Always read and follow the label directions precisely.

Keep Detailed Records

  • Keep all required records on herbicide applications. Expand on that to create a more detailed tracking system for your master maintenance program. Include the following: date of the application; brand name and active ingredients of the product used; rate used and the area on which the application was made; temperature; dew point; humidity levels; wind speed and direction; percentage of cloud cover; soil moisture levels; and any pre- and post-application irrigation and/or precipitation amounts and timing.
  • Record the specifics of cultural procedures. For example, not just the date and core or spike aeration, but core aeration in two directions: north/south and east/west.
  • Add your history with each weed, for example degree-day emergence point, growth rate and stage of growth when any action was taken. When herbicide applications are made, record the plant reaction day by day and the degree of effectiveness. List any reaction to the product by the desired turfgrass within the field and surrounding landscape plantings. Note any feedback from players, coaches, facility administrative personnel, volunteers, event attendees or environmental groups.
  • At the end of the season, review the data. Determine what worked, what didn’t, and, whenever possible, why those results occurred. Review that, and previous years’ data, as part of the process in developing next year’s weed control strategy.