Herbicides
Herbicides represented 87.6% of the total lbs of pesticide A.I. applied including 29 different A.I.’s applied singularly or in combinations (Table 7). The frequency of use by respondents ranged from <1% to 89.2%. Table 7 lists 16 commonly used herbicide A.I.’s. Of the 16, six herbicides were used by approximately 40% of the turfgrass managers surveyed.
The most frequently used herbicide was 2,4-D (amine and ester forms), with 89.2% of respondents having used it. The other four frequently used herbicides were dicamba, mecoprop (MCPP or mecoprop-P), pendimethalin, clopyralid and triclopyr, used by 75.9%, 68.1%, 48.2%, 45.2%, and 39.8% of respondents, respectively.
Five of these herbicides are often used in combination for broadleaf weed control and are found in numerous manufacturers’ products. The exception is pendimethalin, which is used for crabgrass control and is not combined with other herbicides.
Quantities of each herbicide used ranged from 0.4 to 36,713 lbs (Table 7). For eight of the 16 herbicides listed in Table 7, more than 1,500 pounds of A.I. were used, including six of the eight herbicides used most frequently – 2,4-D, dicamba, mecoprop, pendimethalin, clopyralid, and triclopyr. The most commonly used herbicide was 2,4-D with 36,713 lbs of A.I. (32.6% of all herbicides and 28.5% of all pesticide A.I.’s), followed by mecoprop (21,789 lbs), pendimethalin (15,584 lbs), dicamba (5,194 lbs), triclopyr (1,540 lbs), and clopyralid (1,428 lbs).
Two additional herbicides used in large quantities were MCPA and glyphosate. MCPA was used by only 7.8% of respondents, but two respondents collectively applied 22,154 lbs of MCPA in 2001, skewing the results. This quantity represents 20% of all herbicide A.I.’s used, and 17.2% of all pesticide A.I.’s used in 2001. Glyphosate was used by 24.1% of the respondents to prepare lawns for installation and renovation, with a total of 2,090 lbs A.I. applied.
The continued use of clopyralid and 2,4-D, two of the most commonly used herbicides on residential turfgrass, may and will decline in the future due to concerns about impacts on non-target plants and animals. Their use decline will result in increased usage of other herbicide A.I.’s, which can explain the quantities of MCPA used by two of the larger turfgrass managers responding to the survey.
Clopyralid is being removed from the residential turfgrass market because of carry over of the A.I. into vegetable and flower gardens in compost mulch (http://cahenews.wsu.edu/RELEASES/2001/01035.htm) (Caldwell 2001) (http://www.dowagro.com/newsroom/news/041102.htm) (Heine 2002).
The clopyralid is placed on compost piles in grass clippings from lawns treated with herbicides containing clopyralid. The clopyralid is not completely breaking down in the compost pile and when the contaminated compost is applied to garden beds, non-target plants are being injured or killed. As a result of these problems, the registration for usage of clopyralid on residential turfgrass is being cancelled.
One of the most widely used agricultural herbicides, 2,4-D is also one of the most widely used lawn-care herbicides in the United States. It was a common A.I. in all the do-it-yourself programs reviewed for this report (Table 2), and it was also the most commonly used herbicide A.I. and the herbicide A.I. used in the greatest quantity as reported in the survey.
The popularity of the 2,4-D herbicide is due to its effectiveness and relative low cost to use. However, its popularity and frequency of use makes 2,4-D a target of concerns about over use and over exposure of the public.
Concerns about pesticide use are understandable and should be investigated. These concerns are further fueled by statements in the news media about the potential effects of pesticides on human and animal health. The continued widespread use of 2,4-D has been a subject of debate since 1991 when a controversial study was published that purportedly showed a positive association between canine malignant lymphoma and the use of 2,4-D by the dogs’ owners (Hayes et al., 1991). Anti-pesticide-use activists groups have used the results of this study as evidence to support their contention that 2,4-D use is also related to the development of non-Hodgkin’s lymphoma in humans. Numerous studies dispute these conclusions; however, the concerns over the use of 2,4-D persist among the public. In response to these concerns, at least one of the largest national lawn-care companies has replaced 2,4-D in its broadleaf management programs with the herbicide A.I. MCPA (personal communication).
Of the respondents to the survey, most are still regularly using 2,4-D. However, two respondents who manage fairly large quantities of turfgrass had also removed 2,4-D from their programs and substituted MCPA. As a result, MCPA was the second greatest quantity of herbicide A.I. used by respondents to the survey even though its frequency of use was relatively low.
Thirteen herbicides were used in total quantities of less than 40 lbs (Table 7). For this report, these herbicides are being classified as minor-use herbicides. Most of the minor-use herbicides were used by less than 1% of the respondents, and each accounted for less than 0.1% of all the pesticide A.I.’s reported. Many of these products were used for spot treatments only.
To assess how turfgrass managers are using pesticides on turfgrass, the survey asked respondents to provide examples of typical pest-control programs used in 2001, including products used and rates of application. Pesticide usage was further evaluated by associating the information provided in these examples with reported numbers of acres managed and products and quantities used (see Appendix, Survey Questions No. 2 and No. 3, respectively).
For example, the manufacturer’s recommended rates of application for pendimethalin (a pre-emergent annual grass herbicide) on northern turfgrasses are 1.5 lbs to 2.0 lbs A.I. per acre for an initial application prior to weed germination in the spring, and a possible repeat application of 1.0 lbs to 2.0 lbs A.I. per acre after a minimum of four to five weeks for extended weed control or where heavy weed infestations are expected (C&P Press 1996, 1999; C&P Press Web site 2001, 2002).
Thus, a turfgrass manager could apply anywhere from 1.5 lbs A.I. per acre or less with a single application to 3.5 lbs A.I. per acre with two applications at maximum label rates. Pendimethalin was used by 48% of respondents in 2001, with a total of 15,687 lbs of A.I. applied to 22,450 acres, or 73% of all acres reported.
Based on reported quantities used and application rates, 15,687 lbs of pendimethalin A.I. were applied to 9,183 acres, for an average of 1.7 lbs A.I. per acre. This amount is within the total annual recommended use rates for pendimethalin and is only 0.2 lbs A.I. per acre higher than the recommended single application rate.
The percentage of acres treated with pendimethalin by an individual applicator ranged from <1% to 360% (values exceed 100% when more than one application is made to the same area), with 96% of applicators falling between <1% and 150% and 71% between <1% and 100%. Three respondents treated substantially more acreage than the other 77 respondents with 213%, 344%, and 360% of their acres treated, respectively. However, the values may not be accurate. It appears errors may have been made either in reporting formulation of product used or number of acres treated.
The applicator reporting 213% of acres treated may have misreported the formulation used, as no corresponding label could be found, and other applicators used the same product and reported a different formulation. The reports of 344% and 360% of acreage treated by respondents may have resulted from misreporting the numbers of acres managed. In both cases, several products, including pendimethalin, that would normally be used as blanket treatments to all acreage, were reported in quantities great enough to treat areas two to three times larger than that reported. Thus, there were reasons to believe these data were suspect values, and they were deleted from the data set.
Applicators applied less than half the amount of pendimethalin they could have based on labeled rates, and less than five times the amount they could have if they treated all acres under their management, suggesting that this pesticide is used fairly conservatively.
Several of the respondents also included statements about their IPM practices including: