Three percent of the course

A golf course is sprayed for two audiences, the ball and the eye. The ball cares a great deal about a small part of the ground and hardly at all about most of it, while the eye sees everything, so the natural suspicion is that much of the chemistry is for the eye. Nobody has split a course's pesticide use into what is for play and what is for looks, but the measurements that exist divide the question another way. On the putting greens, pesticides buy the game. Across the rest of a course, how much risk is applied tracks what a course is allowed to use and can afford more than the weather it faces, and trials that cut that risk by half or more, mostly by changing products, left disease control and turf quality where they were.

In Denmark every course must report the pesticides it applies and the area of each part of the course, and the environment agency's reporting system turns them into a load per hectare for greens, tees, fairways and the rest of the course.¹ In 2016 greens carried 3.13 units of load per hectare, fairways 0.41 and the rough 0.013; the agency compared the greens with winter cereals, at 2.77, and the rough with grass and clover.² Greens were 3.2% of the land.²

Dollar spot, the most common turf disease of temperate golf courses, left uncontrolled, leaves tan spots 2 to 5 centimetres across that can interrupt both playability and looks.³ On a green, where a putt rolls on the grass itself, a spot that size changes where the ball goes. When Cornell researchers managed some greens at Bethpage State Park on Long Island without chemical pesticides, those of annual bluegrass and creeping bentgrass were often of unacceptable quality and needed an emergency pesticide application in 2002 and several in 2003.⁴ Wisconsin researchers, citing a 2009 long-term evaluation of reduced-pesticide putting greens, write that without pesticide applications greens "are often not able to survive in US climates".³ Greens under integrated pest management at Bethpage received 29 to 46% fewer applications than the unrestricted greens over three years, and their quality equalled the unrestricted greens' for most of the study.⁴

Part of the green's need is made. The US Golf Association gave every member course a Stimpmeter in 1978, and in its suggested speeds a ball-roll distance of 8 feet 6 inches counts as fast for regular membership play.⁵ Turf researchers later blamed it for tighter mowing in pursuit of tournament speeds every day.⁵ By 2009 a Rutgers team gave the preferred daily speed on northeastern greens as 9.5 to 10.5 feet, commonly reached by mowing below an eighth of an inch.⁶ In their trial, mowing at 0.110 inch rather than 0.141 increased anthracnose, a disease that is worse on stressed turf, by 3% to 17% in 2004 and 13% to 21% in 2005.⁶ Mowing twice a day or rolling reached that speed at higher cuts without more disease, though the authors say such practices may reduce the fungicide needed, or space it out, rather than replace it.⁶ In an experiment published in 2001, more than 30 golfers, turf professionals with handicaps from 0 to over 30, could not tell which of two greens was faster when the difference in roll was 6 inches or less, and picked out a 12-inch difference less often on faster greens (68%) than on slower ones (81%).⁵ The faster the greens already are, the less a golfer feels the next foot of speed, and the more the grass pays for it.

Off the green, the ball sits on the grass rather than rolling through it, and a small diseased spot matters far less to the shot. Yet in a 2023 study of acute pesticide risk to mammals on 68 courses, fairways made the largest contribution to total risk in nearly every region except the southern US, where greens did.⁷ Fairways are sprayed less often than greens, but in the Wisconsin researchers' earlier figures they average 11.4 hectares against 1.3, so their applications carry more total risk.³

Two Wisconsin field trials tested how much of that risk is needed.³ In the first, on bentgrass mown as fairway and as green, reduced-risk fungicides timed by a disease forecast cut risk by about 50 to 80%, depending on the measure, with dollar spot control, turf quality and colour no worse than the conventional programmes, at 1.6 to 2 times their cost.³ In the second, from 2017 to 2020, the researchers averaged the fairway fungicide programmes of 23 Wisconsin courses by the hazard quotient, a measure of acute risk to mammals, then took the programme of the course closest to that average and built versions at 75, 50 and 25% of that average by substituting lower-risk products.³ In three of the four years, dollar spot did not differ significantly among the programmes; in the fourth, the full-risk programme had more.³ Turf colour never differed among the four, and in the years when quality did, the full-risk programme scored lowest.³ The quarter-risk programme also cost 10% less.³ The risk it removed bought neither play nor appearance, as far as disease counts, colour and quality scores can show. The plots were a few metres across, the disease was one, and the authors say cuts that large may not be possible on every course.³

The 68-course study was built to test how climate, regulation and money shape the risk, and risk was similar across US regions with varied climates, lower in the UK and lowest in Norway and Denmark; in those three countries 20 or fewer active ingredients were available to superintendents, against 200 to 250 registered for golf courses in US states.⁷ In the northern US, risk rose with maintenance and pesticide budgets.⁷ The Wisconsin authors add that American superintendents often feel pressure from golfers to keep "high quality pest-free playing surfaces".³ The weather, which should decide the need, explains less than the shelf of permitted products and the money to buy from it.

In both Wisconsin trials the fungicide with the single biggest effect on risk was chlorothalonil, which all 23 sampled courses used; the authors cite an estimate that American golf courses account for 10% of the country's chlorothalonil use.³ The European Union stopped approving it in 2019, citing groundwater contamination by its breakdown products and a high risk to amphibians and fish in all the uses it evaluated.⁸

Denmark has capped the load each course may apply since 2013, and between 2013 and 2019 the quantity used on its courses fell by about 77% and the load by about 82%.¹ The fall in load came almost entirely from insecticides, and the fall in quantity from insecticides and herbicides alike; fungicide use barely moved, which the agency puts down partly to fungal diseases that are fairly constant and significant problems.¹ In the first year of the caps, 21% of reporting courses used no pesticides at all, some of them under other restrictions.⁹ Both cut-backs, at Bethpage and in Denmark, hit the same floor, disease control, and both went a long way before reaching it. The Danish agency's evaluation after the first year set out to ask whether courses could keep good playing quality under the caps; its conclusion rests on compliance, and nothing in it measures how the golf played.⁹