Key Takeaways

• Robotic mower use is increasing on golf courses, yet many unknowns remain about how they affect things like turfgrass quality, weed or disease pressure, and the golfer experience.
  
  
• A survey conducted in Europe showed that 90% of responding golfers had positive or neutral feelings about sharing the course with robotic mowers – citing reduced noise, more-consistent turf quality, and better overall playing conditions as key benefits.
  
  
• A research study comparing robotic mowers to conventional reel and rotary mowers on cool-season fairways and rough showed that robotic mowers delivered acceptable turf quality in nearly all situations and delivered better turf quality than traditional units in certain scenarios.
  
  
• Robotic mowing was found to reduce weed and disease occurrence in many settings, most likely due to shorter periods of leaf wetness, reduced plant stress and reduction in weed flowering from more-frequent mowing.
   

One common concern among survey respondents was whether robots might interfere with the game and how to deal with these issues. Interestingly, very few golfers mentioned the same concern about greenkeepers working on the course or operating conventional mowers, which are generally bigger, louder and have more of an impact on the golf experience than small robotic mowers. This indicated the “interference or disturbance with play” response may have been due to golfer misconceptions of how robotic mowers work. 

This highlights the need for good communication with golfers when initially incorporating robotic mowers into a maintenance program so there are no surprises and golfers have an accurate picture of what to expect. It’s also a good time to dispel some myths. For example, prior to the start of the study, it was common for golfers to have concerns about robots hitting golfers or moving golf balls, but this study shows that once they are in use on the golf course, few if any of these concerns materialize. The most-common responses among the few respondents who had negative feelings toward robot mowers included:

• Robotic mowers scaring or hurting wildlife.
  
  
• Hitting the robots with their ball/or that they may be hit by the robotic mowers.
  
  
• It’s annoying when the robot is mowing the landing area.
  
  
• Why can’t the robots mow only at night?
  
  
• Need local rules for balls hitting the robotic mowers.
  
  

Although these responses were uncommon (less than 10% of respondents across three golf courses), it is important to address any concerns golfers may have. Courses can help reduce concerns about robot mowers by communicating what the Rules of Golf say about a mower impacting a golf ball, sharing the specifics of how the mowers work, demonstrating safety features that robot mowers are equipped with, and highlighting the economic and playability benefits.

Overall, 90% of golfers responded to robotic mowers with positive feelings or with similar feelings as they have toward conventional mowers. One of the top positive responses from golfers was not having to wait for greenkeepers to complete mowing with big machines and not seeing or hearing large mowers in areas where robots were being used. The most-common responses were:

• The robotic mowers make the grass more even and dense.
  
  
• The ball lays on top of the grass more.
  
  
• The fairway always looks freshly mown and without clippings.
  
  
• You don’t need to wait for the greenkeepers to finish their job.
  
  
• No noise.
  
  
• The rough feels newly mown every day.
  
  
• Less dew in the morning.
  
  
• Good for environment and economics of the golf course.
  
  
• Gives time for the greenkeepers to do other jobs besides mowing.
   

Both greenkeepers and golfers reported a higher turfgrass quality with robotic mowing due to a more uniform and consistent turf (same quality every day), dew removal and almost no clippings. Turfgrass species at the five golf courses are typical of those on cool-season golf courses in Europe and include bentgrass species, Kentucky bluegrass, red fescue and perennial ryegrass.

As far as disruption to play, robot mowers are all programmed to move around obstacles, including golf balls. During tournaments or times of heavy play, golf course superintendents will typically park the robots just as they would with conventional mowers, so they don’t disrupt play. 

Considerations for Golf Course Superintendents

Golf course superintendents’ qualitative ratings showed that they perceived overall mowing quality to be very high with robotic mowing, and that robotic mowing was superior in the rough compared to rotary mowers. The robots removed dew, produced almost no clippings and labor could be allocated to other tasks on the golf course. However, the first year with robotic mowing was a learning process and challenges included getting electricity out on the course (most eventually used solar power), adapting to a new way of maintenance, and acquiring new tools and parts for the equipment technician to service the robots. An important observation by the superintendents is that it is necessary to change the inexpensive cutting blades on the robots regularly to keep them sharp. As more robots are used on a golf course, a designated staff member may be needed to handle their maintenance and programming.

The demonstration trials conducted on the five golf courses and ratings made by the superintendents indicated there may be differences in weed and disease development in trial areas depending on whether they were mown with robotic or conventional mowers. Trial reports also suggested differences in overall quality after repeated mowing. Therefore, researchers further investigated this in a more controlled environment with an additional study at NIBIO Landvik Research Center and we cover some of the key findings from that study next. The complete results from all study components can be found at NIBIO ROBO-GOLF.

Impact of Robotic Mowers on Turf Quality, Weeds and Diseases

Experimental Design

Field trials designed to compare robotic and conventional mowing of pure stands of colonial bentgrass (Agrostis capillaris), red fescue (Festuca rubra) and Kentucky bluegrass (Poa pratensis) on fairways, and perennial ryegrass (Lolium perenne), red fescue and Kentucky bluegrass in roughs, were established at NIBIO Landvik Research Center in southeast Norway in spring 2020. Husqvarna 550 robotic mowers were used to cut fairways at a height of 0.590 inches and roughs at 1.4 inches. 

Mowing began in April and continued throughout the season. The robots mowed the plots every day for three hours on the fairway and for two hours per day in the rough. Conventional mowing (at the same height of cut as the robots) was done on the fairway turf Monday, Wednesday and Friday with a John Deere triplex mower and on Monday and Friday with a rotary mower in the rough. Knives on the robotic mowers were replaced every four weeks and the triplex mower was backlapped every two weeks. In May, a new front-mounted rotary mower on a lightweight tractor replaced the rotary mower to make the mowing in the rough control plots more comparable to average golf course mowing conditions. The first application of fertilizer was made in April on both fairway and rough plots and the total applied for the year was 1.2 pounds of nitrogen per 1,000 square feet. To simulate wear from golfers, the fairway plots were exposed to a friction wear drum once a week from June to September.

Assessments were conducted on 2-meter subplots within treatment plots, with visual assessments made weekly between noon and 2 p.m., after mowing. Measurements included turfgrass quality, color, weed or disease coverage, and soil compaction/infiltration and were recorded every four weeks from April to October.

Overall Turfgrass Quality

Fairway results

Turfgrass visual quality ratings on the fairway plots varied from 5.0 to 8.5 (1-9 scale) for all assessments, with acceptable turfgrass quality (5 or higher) at all times. In the beginning of the season, no differences between robotic and conventional mowing in the three species were found, but from the end of June and for the rest of the season, robotic mowing in Kentucky bluegrass and colonial bentgrass rated better than conventional mowing. Significant differences between robotic and manual mowing were found in Kentucky bluegrass in June, and in colonial bentgrass in July. In red fescue, robotic mowing was slightly better at some assessment dates and conventional mowing at other dates, but no trend was found. Some differences in actual height of cut were found early in the season, with conventional reel-type fairway mowers producing a slightly lower turf height in the field than robotic mowers, but no long-term trends were observed. 

Rough results

Turfgrass visual quality ratings on the rough plots varied from 4.0 to 8.0 across all assessments with an acceptable turfgrass quality in all treatments except for robotic-mown perennial ryegrass in August-October. In April-May there were no differences between robotic and conventional mowing in the three species, but after June some differences appeared. Robotic-mown perennial ryegrass had a significantly higher turfgrass visual quality in the beginning of June, but after July and for the rest of the season it was opposite and the turfgrass visual quality was significantly lower than the conventionally mown plots in August to October. In red fescue, turfgrass visual quality was higher with robotic mowing in June, but from July through September there was higher turfgrass visual quality with conventional mowing. Significant differences between robotic and conventional mowing in red fescue were found in the beginning of June, August and September – with traditional mowing performing better. The reduced quality later in the season from robotic mowers may have been caused by mowing too often when it wasn’t needed. It is also suspected that variability in weather can impact the growth and quality between species and may have impacted quality ratings independently of mowing treatments. 

Weed Coverage

To investigate the differences between robotic and conventional mowing with regard to competition between turfgrass and broadleaf weeds, three subplots were established in each treatment plot. Subplots were planted with nine plants of plantain (Plantago major), nine plants of white clover (Trifolium repens) and nine root pieces of dandelion (Taraxacum officinale). Few dandelions developed to living plants, so assessments of that weed were cancelled. 

Coverage of the transplanted weeds developed differently in the different grass species, and between robotic and conventional mowing. Coverage of plantain increased only slightly from the initial value of 0.5%-1.0% of plot area with no difference between robotic and conventional mowing. White clover covered about 1% of plot area from June to August and increased to 4.0%-5.5% in September and October, with less white clover in robotic-mown plots. On fairways, encroachment of broadleaf weeds – especially white clover – was observed in both robotic- and reel-mown plots, but the spread of white clover was lower with robotic mowing. Robotic mowing reduced the spread of clover in colonial bentgrass and Kentucky bluegrass by 30% and in red fescue by almost 60% compared to reel mowing.

Observations in 2020 showed that less Poa annua seedheads were found in robotic-mown fairway plots compared to those mown with reel-type mowers. The ability of robotic mowers to remove seedheads from both grasses and weeds on an almost daily basis is a benefit to turf managers, particularly those with mixed creeping bentgrass and Poa annua fairways. As more reel-type robot mowers are introduced and robotic mowers are able to cut at lower heights, benefits in reducing flowering and weed seed management can potentially increase. It was unclear from this research whether robotic mowing would decrease the amount of viable seeds and overall weed pressure or if the primary benefit would be better visual quality during times when weeds are flowering. 

Disease Occurrence and Severity

Up to July, no diseases were found. From the end of July to early October, 2.0%-3.5% disease-affected area was found in colonial bentgrass plots. The diseases were take-all patch (Gaeumannomyces graminis) and anthracnose (Colletotrichum graminicola). The disease incidence in colonial bentgrass was significantly higher than in red fescue and Kentucky bluegrass. In red fescue, less than 0.5% disease-affected area was found from July-September. But in October, 2.5% of the plot area was infected with red thread (Laetisaria fuciformis). A trend for lower disease incidence with robotic mowing compared to conventional mowing was found after July and for the rest of the season (Figure 1). Outbreaks of anthracnose in colonial bentgrass were lower with robotic mowing, which could be explained by the daily dew removal by the robots.

Compaction, Leaf Fineness and Fertilizer Requirements 

From 2020 to 2022, soil compaction was measured annually in August, revealing lower compaction in robotic-mown rough areas, though no differences were found in fairways. After two years, robotic mowing resulted in significantly finer leaves in Kentucky bluegrass and can likely be attributed to higher mowing frequency. Increased tiller density in fairways was found as well, aligning with golfer observations of better ball lies. Despite the hypothesis that robotic mowers would reduce fertilizer demand by returning smaller clippings daily, results showed no difference in fertilizer requirements between robotic and conventional mowing.

Considerations for Golf Course Superintendents

Depending on what grass species are being grown and the type of weed and/or disease pressure, robotic mowing can be a good strategy to reduce outbreaks of these pests on both fairways and roughs. The main benefit in managing disease likely comes through reduced plant stress and shorter periods of leaf wetness from more-frequent mowing. Continuous mowing with robotic mowers could become part of an integrated management program on fairways to reduce dollar spot or other diseases. Further studies should clarify the relationship between robotic mowing and diseases or pests on widely used grasses in the U.S. – like bermudagrass and creeping bentgrass – to better understand the potential benefits of mowing fairways and roughs with robots as well as how it compares to conventional mowers. It is important to note that the dew removal and frequent early morning mowing that led to reduced disease pressure was possible because of the smaller plots and sufficient mowers to, essentially, be continuously mowing through the night. In a practical setting, mowers may not be working through the night. To achieve this benefit across an entire golf course every morning there would need to be a sizable fleet of robots at work.

Robotic mowing on fairways is effective in limiting the negative impact of white clover and other broadleaf weeds on visual turf quality, which is an issue for European greenkeepers that often manage fairways without herbicides. During midsummer, superintendents typically lower fairway mowing heights to remove white clover leaves and flower heads, which can stress turfgrass, especially in dry periods. Robotic mowing at a constant height offers a better strategy, particularly benefiting red fescue and other slow-growing grasses in competition against white clover and other broadleaf weeds. In the U.S., reducing the development of grassy and broadleaf weed flowering and seed development could provide a benefit by reducing the negative impact on visual turf quality from weeds that escape chemical control. Consistent removal of flowers and/or seeds by robotic mowers can potentially reduce long-term weed pressure but the magnitude of this benefit remains unclear.

Final Thoughts and Future Perspectives

Since the start of the ROBO-GOLF Project, robotic mowing on golf courses has increased a lot. Today, bigger robotic mowers are increasing productivity and some robotic options now offer conventional reel-type mowing. In NIBIO’s latest robotic mower project, Fairways4Future, we are investigating combinations of mowing systems and additional turf management aspects of mowing fairways and roughs with robots.

In the meantime, superintendents should be aware that there are some differences in how golfers react to robotic mowers compared to conventional mowers, and that some aspects of turf management can be affected by switching to robotic mowers. Fortunately, the research to this point shows that switching to robotic mowers has either a neutral impact or provides benefits to golf courses.

References

Ferguson, M., Newell, A.J., Bingley, B., & St. Ives Estate, STRI. (2010). Evaluation of the Bigmow automatic mower. Belrobotics S. A Project Number TB101281.

Grossi, N., Fontanelli, M., Garramone, E., Peruzzi, A., Raffaelli, M., Pirchio, M., Martelloni, L., Frasconi, C., Caturegli, L., Gaetani, M., Magni, S., McElroy, J.S., & Volterrani, M. (2016). Autonomous mower saves energy and improves quality of tall fescue lawn. HortTechnology, 26(6), 825-830.

Pirchio, M., Fontanelli, M., Frasconi, C., Martelloni, L., Raffaelli, M., Peruzzi, A., Caturegli, L., Gaetani, M., Magni, S., Volterrani, M., & Grossi, N. (2018). Autonomous mower vs. rotary mower: Effects on turf quality and weed control in tall fescue lawn. Agronomy, 8(2), 15.