10 Serious Weeds of South Florida Golf Courses
The most serious weed of golf turf in southern Florida is goosegrass, followed in estimated rank order by torpedograss, tropical signalgrass, off-type bermudagrass, and crabgrasses.
This was the result of two surveys in 1998 (in Fort Lauderdale) and 2001 (in Naples) of groups of golf course superintendents in southern Florida, adjusted with personal judgements (actual data, Table 1-2). "Seriousness" was defined by superintendents as a combination of complaints by members and loss of use, with a smaller component of the expense of chemical control.
Other weeds that were ranked high in seriousness were sedges, particularly green kyllinga, followed by spurge (probably mostly prostrate spurge), Poa annua, and crowfootgrass. The broadleaf weeds, e.g., dollarweed, pigweeds, and Old World diamondflower, were only important as a group.
In terms of the relative importance of weed control issues, golf course superintendents emphasized clean sprig source, to avoid problems of bermudagrass off-type contamination. Next in importance, they expressed concern about high visibility areas, e.g., clubhouse and areas next to cart paths, as well as weeding and invasion from non-play areas, such as ornamental grass beds and lake margins.
Weed control issues 4 through 8 were spot treatment of goosegrass, communications to members, tracking of overseeded grasses, and interference of late summer preemergence herbicides with overseeded ryegrass. From a show of hands, about 75% of the superintendents in the Naples area did not overseed during the winter of 2000-2001, which may have been a factor in the low emphasis on weed and herbicide issues of overseeding.
Weeds are the second most reported management problem on Florida golf courses, after insects (2). Florida golf course superintendents spend nearly three times as much on herbicides as do superintendents elsewhere, $16,800 per year compared with $6300 elsewhere in the United States (1). A well targeted weed research program must prioritize problems based partly on their seriousness, as well as other factors such as the likelihood of making significant improvements, and the amount of work already being done on a particular problem. For the southern tip of peninsular Florida, we are on the same latitude as no other place in the United States, therefore there may be weed control problems that are unique to our area, and a greater need to understand those unique problems.
To better understand weed problems in southern Florida, two surveys were done. The first, 12 March 1998, involved 99 turf managers, primarily golf course superintendents, attending the 11th annual South Florida Golf Superintendents Association Turf Expo, at Fort Lauderdale Research and Education Center. (The group included 15 sports turf managers, who also maintain bermudagrass turf.) Respondents were asked to rank the relative seriousness of various weeds (Table 1) on a 1- to 3 basis, with 1=most serious. They also added any weeds missing from the list of nine choices, ranked the factors contributing to the "seriousness" of a weed problem, and ranked the effectiveness of the top three preemergence herbicides for goosegrass control in bermudagrass turf (results not presented).
The second survey, 29 January 2001, involved 56 primarily golf course superintendents, attending the Everglades Golf Course Superintendents Association meeting in Naples, Florida. Superintendents were asked to rank the relative seriousness of various weeds on a 1- to 8 basis, with 1=most serious (Table 1). They also ranked the importance of weed control issues (Table 2), and added any weeds missing from the list of 12 choices. Unfortunately, green kyllinga, which was on the first survey, was not on the second survey.
Rank scores were inverted to fractions, thus 1 was converted to 1, and 2 was converted to 0.5, and 3 was converted to 0.333. Inverted rank scores were converted to relative values, based on the sum of inverted ranks for each observer. For example, if someone only ranked two weeds, 1 and 2, then the relative rank for weed 1 would be 1/1.5 or 0.667, and the relative rank for weed 2 would be 2/1.5 or 0.333. This way, each individual's rankings had the same value, and the converted scores gave a diminishing credit to a weed, depending on how low it was on the list of people's seriousness ranking. The sum of relative inverted rank scores was found for each weed and each weed control issue, and these were converted to an overall percentage of the sum of all accumulated units scores for all weeds.
Goosegrass was the most serious weed in golf turf, and was rated #1 in both 1998 and 2001. This is consistent with the 1996 Golf Course Superintendents Report, in which goosegrass was also listed as the highest problem intensity weed in the Florida region.
Four weeds followed goosegrass in average seriousness, but none was consistently in second place. For example, off-type bermudagrass was in second place in 2001, but in only ninth place in 1998. Crabgrasses were in second place in 1998, but in fifth place overall in 2001, meanwhile the average of scores across years was tied for second place between crabgrasses and torpedograss. Considering that crabgrasses are frequently misidentified as tropical signalgrass, I have tentatively moved the crabgrasses from the second or third place to the fifth place. That allowed room for offtype bermudagrasses in fourth place, even though they were solidly in second place in 2001. I have moved tropical signalgrass up from fourth place (where it was in 2001) to third place, leaving torpedograss as the second-place weed in terms of seriousness.
Sedges were not asked about in 2001, but there were 20 write-in votes for sedges, mostly not specific, "sedge," although three respondents indicated that kyllinga was serious. The remaining "serious" weeds rounded out the list of the top nine, and they are approximately equally ranked, e.g., spurge (probably mostly prostrate spurge), Poa annua, and crowfootgrass. It was surprising that crowfootgrass exceeded Poa annua in importance, particularly for a survey taken in the coolest month of the year, when Poa annua would normally be in its most prolific condition. Nevertheless, a show of hands at the 2001 meeting revealed that approximately 75% of the superintendents had not overseeded. There were eight write-in votes for pigweeds (including five for redroot pigweed, almost certainly another misidentification), and five for doveweed, which is frequently misidentified as Old World diamondflower. Collectively, the broadleaf weeds should be on the list of ten most important weeds.
Importance and weed research priorities
Goosegrass is easily prevented on south Florida golf courses by several
preemergence herbicides. Unfortunately, the cost of season-long protection
is considered too great for some golf courses to be on a regular program,
thus they get into a pattern of spot treatment, which should be the method
of last resort. Research should focus on improving the timing of preemergence
application, and the need to investment in consistent treatments, to reduce
the goosegrass seed bank. Torpedograss is a potential problem everywhere
on the golf course, including mitigated wetlands and native grass plantings.
While Drive 75DF lessens torpedograss, it requires more than one year
of treatment to remove it entirely. A complete program of torpedograss
removal must address the problem along lake margins and wetland areas.
Tropical signalgrass can be controlled with two to four postemergence
applications of MSMA, but the problem is often allowed to get out of hand
because of misidentification, and failure to follow through with multiple
treatments. The increase reliance on preemergence herbicides for goosegrass
control has probably left the golf course vulnerable to seedling germination
of tropical signalgrass. Companion work on sod farms shows that tropical
signalgrass is difficult to prevent with existing preemergence herbicides.
The crabgrasses are closely related to tropical signalgrass, but much
easier to control. Areas with a crabgrass problem have probably not had
MSMA applied on a regular basis. Among the sedges, large areas of green
kyllinga often infest the fairways. This is primarily a problem in late
fall and early winter, as the kyllinga seems to fade out between March
and April. Only Manage, Image, and MSMA+Sencor are highly effective against
kyllinga, but Manage is the least likely to injure the bermudagrass. There
are many excellent phenoxy broadleaf mixtures, although there is some
uncertainty about which to use on difficult tap-rooted weeds. Manor herbicide
and possibly Lontrel are the best backups for very difficult broadleaf
weeds. Other mixtures for the future may include carfentrazone. Poa annua
is the main weed of perennial ryegrass overseeded into bermudagrass turf.
It is hard to control because of the risk of injurying both the perennial
ryegrass and the underlying bermudagrass turf. While this is a niche problem,
it deserves more careful research.
Table 1. Weighted importance, average importance, estimated rank, and comments on weed seriousness surveys, Fort Lauderdale (1998) and Naples (2001). Tropical signalgrass was switched with crabgrasses because of its common misidentification.
Table 2. Importance of weed control issues in January 2001, based on weighted ranks of
1. Anonymous. 1996. 1996 Golf Course Superintendents Report, Golf Course Superintendents Association of America, Lawrence, Kansas.
2. Hodges, A. W., J. J. Haydu, P. J. van Blokland, and A. P. Bell. 1994. Contribution of the turfgrass industry to Florida's economy, 1991/92: A value added approach. University of Florida IFAS Economics Report ER 94-1.
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