Taking control: Implementing effective weed management practices

Updated Jan 17, 2020
Photo: PixabayPhoto: Pixabay

In the wintertime, weeds are probably the last thing on your mind, but soon enough spring will be here and these unwelcome lawn intruders will be rearing their ugly heads once more.

If you’ve found yourself frequently having to deal with customer callbacks to deal with weeds, now is a good time to evaluate your program and see if there are any practices that you can change to minimize infestations.

“Weeds are the result of poor turfgrass performance, not the cause of it,” says Rob Golembiewski, Ph.D., Bayer Green Solutions Team.

By keeping this in mind, examine what may be the cause of poor turfgrass performance before turning to herbicides. The causes of a struggling lawn can be natural, such as high foot traffic, diseases or insects or cultural, such as improper fertilization, excessive thatch, incorrect mowing height/frequency or inappropriate irrigation.

Golembiewski says lawn care operators should opt for an integrated weed management program to reduce outbreaks. The five elements it includes are prevention by using weed-free sod, mechanical controls by hand pulling, cultural strategies, biological control and chemical control.

“Of these five, lawn care operators should address cultural strategies first or in conjunction with an effective herbicide program,” he says.

The cultural strategies include mowing at the proper height and frequency, having adequate drainage, timely aeration, proper irrigation and proper fertilization rates and timing.

“After addressing cultural practices with the customer, choosing the correct herbicide and rate along with the correct application timing and technique are all critical for successful weed control,” Golembiewski says.

Best practices for using pre- and post-emergence herbicides

Pre-emergence herbicides are applied, like the name implies, before weeds have emerged and can provide good control if used properly.

“Pre-emergence herbicides are only effective on weeds prior to emergence so they are useful primarily on annual grasses and some annual broadleaves,” Golembiewski says.

Golembiewski says some of the best practices when it comes to using pre-emergence herbicides are to apply it at the appropriate rate prior to weed seed germination, which varies based on the targeted weed species.

Irrigation or rainfall is needed to move the herbicide down to the soil so if irrigation is not available, be sure to apply it well in advance of weed germination to allow for an activating rainfall. However, avoid applying pre-emergence herbicides when excessive rainfall is forecasted.

Golembiewski notes that loss of activity may occur for many pre-emergence products if it is not watered in within seven to 10 days. If you need a larger window of time, he says Specticle FLO needs to be watered-in within 21 to 28 days.

He also says to not mow or collect clippings before the herbicide has incorporated into the soil.

As for post-emergence herbicides, Golembiewski says it is best to apply these to younger plants, so strive to target applications early in weed development. He says sprays give better control than granules.

Avoid applying post-emergence products in extreme temperatures. Golembiewski advises applying anywhere from 40 to 80 degrees Fahrenheit.

You should not mow for 24 to 48 hours before or after an application and do not irrigate 12 to 24 hours after an application. Post-emergents need at least four hours that are rain-free.

If dealing with difficult weeds, repeat applications may be needed.

Common weed control mistakes

According to Golembiewski, three main weed control mistakes lawn care operators make are opting for inexpensive pre-emergents, not rotating herbicides and using lower than recommending herbicide rates.

“Though responsible buyers always look at price, it is critical to compare ‘apples to apples’ and compare cost/acre between products,” he says. “Cost per acre between two similar products could differ dramatically if application rate is lower for one product compared to the other.”

For example, Specticle FLO is applied at a much lower rate than products like pendimethalin or prodiamine. He also says experienced buyers will look at the price per acre per days of expected control. While one product has a longer duration of control, others may not.

“The take-home message is that spending a little more upfront may save you much more later this season in customer satisfaction and call-backs due to failing control,” Golembiewski says.

To calculate cost-in-use for pre-emergence herbicides, check out Bayer’s online tool.

Another common mistake is to fail to rotate herbicides with different sites of actions, as this minimizes the chances of herbicide resistance in weeds. However, this is a challenge with pre-emergence herbicides as there are only a few modes of action available.

“In warm-season turf, managers can rotate every 3rd or 4th year from Specticle (WSSA Group 29 mode of action) to pendimethalin, prodiamine or dithiopyr (all Group 3 modes of action),” Golembiewski says. “Using a post-emergence herbicide like Celsius or Tribute Total later in the summer can further reduce the risk of resistance because these products have distinctly different modes of action than the pre-emergence herbicides. Rotating pre-emergence herbicides on cool-season turf is impossible since only herbicides from Group 3 are labeled (pendimethalin, prodiamine or dithiopyr). Though resistance to this group of pre-emergence herbicides is not yet reported in cool-season turf, incorporating a post-emergence herbicide like Acclaim Extra later in the season can help limit the chance of resistance.”

While a lawn care operator may think they are creating savings by using less of a herbicide product than the recommended rate, it tends to lead to more issues that will cost more money in the grand scheme of things.

“This will usually result in breakthrough and/or the need for a repeat applications, not to mention customer dissatisfaction, which is far more expensive and time-consuming than using the proper product at the appropriate rate,” Golembiewski says. “It is important that all products be applied according to the label directions.”

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