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Frank S. Rossi, PhD
Frank S. Rossi, PhD

Gazing in the Grass...

Studying mowers no open-and-shut case



Sometimes what seems like a simple question opens a can of worms. Four years ago, I wondered if greensmower designs, particularly cutting-head design (fixed, flex or floating), influenced turf performance and stress-related disease, i.e., basal rot anthracnose.

The phrase “can of worms” is believed to be a metaphor coined in the 1950s. Fishermen, after buying live bait from a bait store, learned the hard way how easy it was to open a can of worms and how difficult it was to close one. Once the worms discovered an opportunity to escape, it became nearly impossible to keep them contained.

I admit to opening a can of worms thinking it was a can of tuna – only to realize four years later that I can see the “worms” better, yet I am still formulating a containment strategy. If I’ve lost you by now, the issue is this: What started out as research into mower-head design has evolved into an exploration into some of the most fundamental aspects of reel mowing.

The can opener
Basal rot anthracnose was at epidemic levels in 2004, with little understanding of primary stress causes beyond close mowing and stress. Research at Rutgers University focused on fertility, plant growth regulators, vertical mowing, etc. The primary issue identified in that early research was nitrogen level. Raising rates from 1.5 pounds to 3 pounds per 1,000 square feet per year significantly reduced anthracnose.

It had always been assumed that the movement toward lower mowing heights also was a prominent factor. Some height research was conducted, but no one was asking the question about different mower design.
The preliminary results drew a lot of attention. It seemed that certain mowers and head designs led to more problems with anthracnose.
We simply took the mowers we were loaned from the companies and compared them at field mowing heights around one-tenth of an inch. Field mowing heights meant they were set at different bench settings. That’s all we did – rollers were different, bedknife set-up was different, frequency of clip, etc., were all unaccounted for. This was not solid research methodology, primarily because I thought it was tuna fish (easy to contain), not worms.

The preliminary results drew a lot of attention. It seemed that certain mowers and head designs led to more problems with anthracnose. We were roundly criticized for our methodology, which certainly was flawed, yet what we observed must have been related to something regarding the mowers.

Worm-watching
Once the preliminary data were circulated, all the major mower companies were interested in participating in a larger comparison of mowers. At the same time, we refined our evaluation protocol (cut quality, ball roll, etc.), assessments improved regarding mower design and adjustments (weights, clip, bedknives, rollers) andmanufacturers began developing alternative power sources (e.g., electric).

After three years of conducting the evaluation of the mowers, I know our findings are very difficult to interpret. There are so many potential factors that are different beyond head design such as weight, clip, bedknife position, etc. that I am reluctant to draw any meaningful conclusions.


Cornell University associate professor Frank Rossi, left, and research assistants Brett Welch, center, and Nick Gardner assess mower cut quality in a field study. (Photo courtesy of Mary Thurn)
Certainly some mowers resulted in a cleaner cut and sometimes that translated to ball roll. Some mowers were more likely to result in increased stress-related diseases, but often that was highly dependent on mowing frequency, i.e. number of double cuttings per weeks.

We learned some important logistical aspects of mower design. Fixed-head mowers come out of adjustment, both in height and relationship to bedknife, more than flex or floating heads. Fixed-head mowers greater than 18 inches tend to be more prone to scalping when the surface has been softened by rainfall and when surface organic matter is not properly managed. The latter point is directly correlated to stress-related disease; if you scalp, you get anthracnose.

Worm containment
I learned as a young scientist that research often raises more questions than it answers. In this case, and to their credit, each manufacturer became actively involved in assessing their own technology from an agronomic perspective. Of course, I was slightly surprised there was not a more thorough understanding of some of the agronomic issues we raised, though maybe there is and I am not privy to the information.

The precision of our research has evolved, as we are investigating the role of bedknife positioning relative to the centerline of the reel. The working hypothesis is that as bedknife position moves further back from the reel, the more aggressive the cut. We have identical mowers all set up the same except for bedknife position. The positioning is determined by bedknife length, reel roller adjustment and bedknife bar.
The precision of our research has evolved, as we are investigating the role of bedknife positioning relative to the centerline of the reel.
As we began to talk about this work with superintendents and asked them if they knew about bedknife length and position, most if not all were completely unaware of the adjustment. Most knew about bedknife thickness, but few knew anything about the role of bedknife position on cut.

With expanding electric technology, we have also developed a program assessing the effects of various frequencies of clip on putting surface performance. We are testing the “rule of thumb” that ideal cut quality is achieved when the frequency of clip (a function of reel speed, ground speed and number of blades on the reel) matches mowing height. I am not aware of any studies or greensmowers that prove this.

Now that the worms are loose, I am pleased that we have facilitated a discussion about this important topic among academics, manufacturers and superintendents. I look forward to many more experiments; as an extension scientist, I have always viewed this as part of my job. Now, instead of recapturing the worms, let’s work on learning how to use them to catch fish.


Contributing editor Frank S. Rossi, Ph.D., is associate professor of turfgrass science at Cornell University in Ithaca, N.Y. He can be reached at fsr3@cornell.edu.




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