Applied Research and the Bottom Line: Turf and ornamentals work at the Kao-Kniffin lab

By Michelle Sutton

Cornell University Assistant Professor of Horticulture Dr. Jenny Kao-Kniffin is “working on a bunch of integrated research projects about how to manage weeds in landscapes and turf without the need for pesticides.” Her ability to handily boil down sophisticated research into plain language is something she uses daily in her outreach and extension work as a weed ecologist of urban landscapes.

Kao-Kniffin runs a lab at Cornell with the overarching focus of studying the belowground ecology of invasive plants and weeds. Her research is mostly of the applied variety, because it seeks to solve particular problems or answer practical needs. It’s the kind of research that will directly affect a landscape and turf professional’s knowledge base and bottom line.

School Grounds, Research Grounds 

In 2010, New York State passed the Child Safe Playing Fields Law (CSPFL), which restricts the use of conventional pesticides from K-12 school grounds, playing fields, and daycare centers, both public and private. Connecticut already had a similar law in place for schools through 8th grade; Massachusetts has regulation, albeit less stringent; and many other state legislatures like those of New Jersey and Maine are considering bans.

There’s huge momentum here that can be expected to eventually extend to public lands beyond school grounds and playing fields, and it’s going to affect landscapers and their options for weed control. The good news is that Kao-Kniffin and colleagues are researching alternative means of effective weed management, and are keen to share their findings with lawn care companies and school facilities managers.

Kao-Kniffin has partnered with a pilot group of four school districts to manage their playing fields, primarily soccer fields, and to conduct original research there. “We’re starting off small this year; then, based on the results, we will expand into different areas of New York, but also Maine and Massachusetts.” She and her team are talking with school facilities managers and eventually lawn care professionals too, as many school districts are increasingly contracting out field management to commercial lawn care providers. 

The chemical breakdown

Kao-Kniffin gets frequent inquiries from companies about what pesticides are allowed to be used on school grounds. Even schools that don’t fret over aesthetics have to be able to control clover, for example, because the risk of bee stings to children poses a liability. Prior to the enactment of CSPFL in New York, schools used glyphosate-based products, but that is not permitted under the ban.

Kao-Kniffin studied the list of organic pesticides that are approved by the Organic Materials Review Institute (OMRI) to determine which of these were allowable under the CSPFL (for example, 20 percent acetic acid is OMRI-approved but is considered a risk to children by CSPFL). She had to consider both the active and inert ingredients to make sure they were EPA-classified as minimum or reduced risk. The list of organic pesticides that met all these criteria was very short.

She and fellow weed scientists from Cornell Turfgrass and the Long Island Horticultural Research & Extension Center (LIHREC) evaluated those minimum- and reduced-risk herbicides for use on turfgrass. They found that the most effective herbicide was likely to be cost prohibitive for most schools. (Read about this at [ital><ital]).

“Until more effective organic herbicides are available at an affordable

cost, school grounds management in New York State will need to adopt non-chemical weed control options,” said Kao-Kniffin.

Culture saves us 

The first study involving cultural methods for weed control uses repetitive overseeding, which is not a new concept, and is routinely used on golf courses in the South, but hasn’t been implemented as a routine strategy on school playing fields in the North.


“In overseeding, grass seed is sown in the late summer or early fall and sometimes in the spring to mimic the natural ecosystems of grasslands,” said Kao-Kniffin. “It replenishes the density of the turf, which suppresses weeds by shading out competitors, and it increases the field’s playability. When you have a dense cover of turf, weed seeds don’t have the opportunity to germinate, so it’s a natural weed-suppression strategy.”

Kao-Kniffin’s study will use perennial ryegrass — a grass species that germinates rapidly, often within three days with enough moisture.

The next study involves using fertilizer at the proper rate and calibration so that nitrogen works its magic to encourage greater turf density, which crowds out weeds.

“Some contractors go overboard with adding fertilizers,” said Kao-Kniffin. “This can result in excessive phosphorus application, whereas nitrogen should really be the focus when it comes to turf density in most sites.”

Furthermore, in New York and many other states, phosphorus bans apply because of their damaging effects on aquatic ecosystems.

A third study involves topdressing sod for school grounds and playing fields with organic amendments such as vermicompost (worm-composted farm waste) and composted yard waste. Kao-Kniffin said that several sod farms in New York have agreed to collaborate with Cornell researchers on the project if the scientists obtain research funds for the initial work. Already, a sod farm has started a trial evaluation of vermicompost, applying 20 pounds of the compost per 1,000 square feet of sod. That translates into an application rate that is economical if the grower is saving in the costs of production (mowing, irrigation, and fertilizer and pesticide applications).

This year, they dug up/sampled some of the vermicompost-enriched sod and found a significant enhancement of root growth compared to sod that was not grown with vermicompost.

“One of the sod growers said that at this rate of growth, they might be able to harvest sod earlier, which means turning over the product faster, which saves on labor costs and inputs,” said Kao-Kniffin. “This could make turf more economical to produce; compost manufacturers are very interested in the findings of this research.”  

Kao-Kniffin’s colleague at the New York State Agricultural Experiment Station in Geneva, N.Y., entomologist Karl Wickings, has submitted a proposal to the USDA seeking funding to get researchers and industry stakeholders like turf managers, compost manufacturers, and sod farmers together to talk about how to create sod that is more sustainable. They are hoping to get funded for that next year.

Kao-Kniffin also does research at the microbial level, looking for beneficial microorganisms including fungi and bacteria that could be introduced to turfgrass and work symbiotically with it. “That research is fundamental — i.e., not practical yet,” she said. “But the ideal situation is that in 10 years we might have some commercially available inoculants and/or promising genotypes of turf and ornamentals that can attract beneficial microbiota to the roots.”

Healthy turf is dense, and more resistant to pests. Kao-Kniffin said that as pesticide restrictions multiply in the U.S., there will be a demand for this kind of “superturf” — one that doesn’t require so many chemical inputs. Once her lab isolates these microbiota and exceptional genotypes, they will bring this information to the landscape industry.

As above, so below

Grant Thompson is a graduate student working on his master’s and doctoral degrees with advisor Kao-Kniffin. In his research at Cornell, Thompson has looked at urban grasslands and turfgrass systems through the lens of biodiversity and ecosystem functioning (BEF).

BEF theory has been applied to many ecosystems, such as prairies and forests. Thompson said that it has generally been found that an increase in biodiversity increases ecosystem functioning — nutrient cycling, rate of generation of biomass, pest resistance, etc.

“In our research we looked at monocultures and polycultures of commercial turfgrass species,” he said. “A monoculture would be Kentucky bluegrass exclusively, for instance, while the polycultures included mixes of tall grass fescues, fine fescues, supine bluegrass, annual bluegrass, Kentucky bluegrass, and micro-clover.”

Thompson’s research took place under controlled greenhouse conditions for five months. How did the turfgrass monocultures and polycultures compare?

“In the polycultures, we found some moderate increases in biomass and some moderate retention of nitrogen,” he said. “Interestingly, we also found that the rhizospheres (root zone) of the polycultures contained more diverse soil bacterial and fungal communities. You could say that the below-ground diversity mirrored the above-ground diversity.”

Thompson said he doesn’t yet know the full implications of that biodiversity in terms of turf performance, but he and Kao-Kniffin took away that BEF theory might also be applied to lawns and, by extrapolation, to other urban managed landscapes such as ornamental gardens. Bearing in mind that this greenhouse study would need to be replicated in field settings, Thompson said this study shows that turfgrass polycultures contribute to soil microbial diversity and they enhance grass biomass while decreasing leaching of nitrogen from soils. This is in line with the consistent findings of BEF that biodiversity supports multiple ecosystem functions.  

What are the implications of Thompson’s research for turf managers and landscapers? He said that for the high-intensity, large-area turf managers such as golf course supervisors, they have systems in place for managing monocultures. Yet in roughs and fairways, increasing turf diversity could be beneficial. For the lower-intensity, lower-input landscapes such as municipal parks and residential lawns, turf polycultures are also viable.

Said Thompson, “Landscapers and turf care companies should think about increasing diversity in their landscape at all levels — genus, species, and cultivar — and should think about their landscapes in terms of ecosystem services in addition to aesthetics.”

Michelle Sutton ( is a horticulturist, writer, and editor.

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