The bane of any grower’s work outdoors, from planting to germination to growth to harvest, is weeds. They can be rather determined when it comes to competing for light, water, space and nutrients.

There are people out there who focus solely on how to manage them. Jared Hoyle, Ph.D., a turf and ornamental market development specialist with Corteva Agriscience, is one of them.

“I love killing weeds,” he admitted during his presentation at Cultivate’24. “But learning what not to do is sometimes better than not learning what to do.”

He works with Corteva’s research and development team to figure out not just how to kill weeds but to help growers better their businesses.

So why is weed control so important in landscapes? There are often diverse mixes of ornamentals (annuals and perennials, herbaceous and woody, upright and groundcovers). They are often in frequent view of property owners and in regular proximity to client’s personal space. Desired plant health is regularly observed (and sometimes even illuminated at night). And there is a broad range of weed species infesting landscapes.

“It’s important to focus on the positive instead of the negative,” Hoyle said.

Landscaped settings tend to be challenging because hand-weeding is very time-consuming, each site’s landscape is different, post-emergence herbicides can injure adjacent plant material and, along those lines, odors/stains are intrusive to clients.

In true Ph.D. fashion, Hoyle developed a function formula to find weeding productivity. It helps him to select herbicides for specific landscaping jobs. “You need to pick the right one for the right job,” he said.

First, look at your application cost (price, method, product, labor) and multiply it by the area to be covered (the area of effective weed control – the weed species) and plant tolerance.

Then divide that figure by the duration of control (the length of time of acceptable weed control).

The final number equals your agronomic and economic productivity – the value to you and your practice.

Three Options for Weed Control

Hand-weeding, pre-emergence and post-emergence herbicides are the three main options for weed control.

In regards to that onerous task, Hoyle also created a “calculator” to find the hand-weeding impact on your business. First, note the average length of time it takes to hand-weed 1,000 square feet. Then note the cost to hand-weed per hour (your labor cost). Next, note the number of acres to hand-weed. Finally, write down the number of times you need to hand-weed each year.

In a hypothetical example, he said if it takes 30 minutes to hand-weed 1,000 square feet at $20/hour – and there are five acres to weed, six times a year – the total hand-weeding cost can be more than $13,000.

“You get instant gratification with hand-weeding but it may only be instant control,” Hoyle said. “Post-emergence herbicides can lower that cost by 75%.”

Post-emergent treatments only (what Hoyle called “the Roundup approach”) can be problematic for a number of reasons. The regrowth of weeds leads to multiple applications throughout the season (which is labor intensive and therefore expensive). There are ornamental and turf safety concerns due to the applicator trust factor. Dead vegetation throughout an area can be aesthetically displeasing depending on initial weed pressure.

There’s also the public perception of this method – people seeing applicators in hazmat suits with backpacks full of chemicals.

There is also the pre-emergent herbicide option. But a survey from Specialty Consultants found that only 65% of applicators treat residential and commercial landscape beds with pre-emergents.

“Pre-emergent use in both turf and landscape beds leads to time and labor savings, can help ease public perception and free up more time for other aspects of your business,” Hoyle noted.

Pre-emergent herbicides typically work well if they are applied prior to weed seed germination; they are applied at the correct rate at the correct time; they are activated with the appropriate moisture; the chemical barrier is not disrupted; and your herbicide of choice is labeled to control the weed.

“Customers will forgive you for a few escaped weeds but not for killing one of their plants,” Hoyle said.

That’s why it’s important to learn and understand the plant lifecycles of the weeds you are seeking to control. Create a weed control program for landscape beds and turf based on your customer needs and your company strategy – there is no one-size-fits-all.

(Hoyle also recommended reading “Turfgrass Weed Control for Professionals” from Purdue Extension. Find it at edustore.purdue.edu/turf-100-w.html.)

by Courtney Llewellyn