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© 2010 Plant Management Network.
Accepted for publication 30 June 2010. Published 13 July 2010.

Influence of Foliar Moisture on Postemergent Granule Herbicide Control of White Clover and Dandelion in Cool-Season Turf

Daniel L. Loughner, Field Scientist, and Steven P. Nolting, Research Scientist, Crop Protection Research and Development, Dow AgroSciences, Indianapolis, IN 46268

Corresponding author: Daniel L. Loughner. dloughner@dow.com

Loughner, D. L., and Nolting, S. P. 2010. Influence of foliar moisture on postemergent granule herbicide control of white clover and dandelion in cool-season turf. Online. Applied Turfgrass Science doi:10.1094/ATS-2010-0713-01-RS.

Abstract

Field studies were conducted in 2007 and 2008 to determine the influence of foliar moisture on the performance of three postemergent granular herbicides against white clover, Trifolium repens L., and dandelion, Taraxacum officinale (Weber). The herbicides utilized were LockUp 3-Way (2,4-D/penoxsulam/dicamba), Scotts Turf Builder with Plus 2 Weed Control (2,4-D/MCPP-p) and Lebanon ProScape Fertilizer with Trimec Herbicide (2,4-D/dicamba/MCPP-p). Herbicides were applied to individual plots in the morning when dew was present and then later the same day when foliar moisture had dissipated. Weed control was assessed at intervals of approximately 2, 4 and 8 weeks after treatment. The presence of foliar moisture generally improved the performance of all herbicides evaluated. Given that commercial applications generally target a complex of weeds the results indicate that optimum performance of granular postemergent herbicides will occur when applications are made to moist foliage.

Introduction

White clover (Trifolium repens L.) and dandelion (Taraxacum officinale Weber) are weeds common to most turfgrass sites throughout the United States. Lawncare professionals and golf course superintendents identify these weeds as the most troublesome and difficult to control (2). It is believed that white clover was introduced into the United States by European settlers and was known to exist in Kentucky and Ohio by the mid-1700s (11). Dandelion was brought to the United States by Puritans in the 17th century as a source of medicine (5). Since their introduction, both weeds have spread throughout North America.

White clover and dandelion are perennial weeds with distinctly different growth and reproductive characteristics. White clover has a stoloniferous growth habit defined as low-growing branched stems that root at the nodes. Flowers are produced throughout the summer and reproduction occurs through seed dispersal and stolons (12). Dandelion produces a taproot from a basal rosette of leaves. Yellow flowers are produced on a leafless stalk with maximum flowering occurring in the spring followed by a secondary peak in the fall (4). Reproduction occurs through wind-blown seed dispersion and by new shoots that develop from broken segments of the taproot (12).

Control of white clover and dandelion is most often achieved by practitioners with preformulated herbicide mixtures. The most widely used granule mixtures throughout the United States are 2,4-D/MCPP and 2,4-D/MCPP/dicamba (7). These mixtures are often used by turf managers when applying liquid formulations is not practical or feasible and by homeowners as a matter of convenience.

The performance of current postemergent granule broadleaf herbicides is influenced by foliar moisture on target weeds at the time of application. The moisture improves the adhesion of the granule to the foliar surface (1). Turfgrass managers are not always able to make granular applications to moist foliage due to scheduling and homeowners tend to apply materials when convenient without respect to the presence of dew or foliar moisture. Previous research has demonstrated that granular herbicide combinations of clopyralid+triclopyr and 2,4-D+mecoprop+dicamba applied to moist weed foliage perform better than the same combinations applied to dry foliage (6,10). Our objective was to evaluate the effectiveness of a newly introduced postemergent granular herbicide applied to moist and dry weed foliage.

Comparing Granule Postemergent Herbicides

The performance of postemergent granule herbicides was evaluated across ten field studies conducted in mixed stands of established cool-season turf over a two year period, 2007-2008 (Table 1). Studies compared the performance of three herbicides against white clover and dandelion when applications were made to moist and dry weed foliage. Experimental design in each study was a randomized complete block having a minimum of three replications. A factorial set of treatments were constructed from the three herbicides and two application moistures; an untreated control was included for comparison. Individual plot sizes ranged from 12 to 30 ft². The treatments compared were LockUp 3-Way (Dow AgroSciences, Indianapolis, IN), Scotts Turf Builder with Plus 2 Weed Control (The Scotts Company, Marysville, OH) and Lebanon ProScape Fertilizer with Trimec Herbicide (Lebanon Seaboard Corp., Lebanon PA) (Table 2). Herbicides were applied in the spring when dandelion was beginning to flower. This generally occurred early to mid-May. Materials were applied the same day, in the morning when dew was present and again later when moisture had dissipated from the weed foliage. Individual treatments were applied using a splitter box (3) or shaker-jar, uniformly dispersing granules across the plot area.

Table 1. Location by state, of granule herbicide comparison
studies conducted in 2007 and 2008.

Table 2. Herbicides and fertilizer analysis, granule particle size, product rates and active ingredient (ai) or acid equivalent (ae) applied to study sites in 2007 and 2008.

 * SGN = Size guide number (calculated diameter of the "average particle" expressed in millimeters to the second decimal and then multiplied by 100).

Study sites were fertilized and irrigated as necessary to promote active turf and weed growth and avoid drought stress. Turf was maintained at 1.5 to 2.5 inches depending on study location. Weed control was determined at approximately 2, 4, and 8 weeks after treatment using the formula [1-(B/A)] * 100, where A is the percent weed cover in each plot at the day of application and B is the percent weed cover at a specific interval after application. Therefore, ratings range between 0 and 100 percent where 0 is no control and 100 is complete elimination of the target weed. Data were analyzed using mixed linear models appropriate for trials conducted across locations (8,9). The effects for location, rep within location, treatment by location, moisture by location, and treatment by moisture by location were treated as random factors. Differences in -2 log likelihood values between models with and without the treatment by location and moisture by location interactions were compared to a Chi-square value with 1 degree of freedom at alpha level 0.05 to determine if location interacted with treatment or moisture factors. Where significant differences were observed a Tukey, or for unbalanced data, a Tukey-Kramer test was used to separate treatment means. All evaluations and comparisons were performed using an alpha level of 5% except where noted.

Results of Trials Comparing Postemergent Granule Herbicide Performance When Applied to Moist and Dry Weed Foliage

There were no interactions observed between location and treatment or moisture indicating treatment and moisture effects responded consistently across locations for dandelion and clover at all evaluation intervals. No interaction was observed between treatment and moisture factors at any evaluation interval making it possible to independently assess treatment and moisture effects within each of the evaluation times.

White clover. The highest level of control for treatment and moisture factors occurred at the 4 WAT evaluation (Tables 3 and 4, Figs. 1 to 4). Averaged numerical levels of control observed with the herbicides were consistently ordered, LockUp>Trimec>Plus 2. LockUp treated plots had higher levels of control when compared to Plus 2 plots at all evaluation intervals and Trimec treated plots at 4 and 8 WAT. No differences in levels of control were observed between Plus 2 and Trimec. Having moist foliage at the time of application improved clover control at evaluations made 4 and 8 WAT. At the 2 week evaluation the P>F was 0.083.

Table 3. Mean white clover control across study sites at various
evaluation timings.

Means followed by the same letter within an evaluation date are
not significantly different (alpha = 0.05).

Table 4. Mean white clover control across study sites at different
application foliage moistures.

Means followed by the same letter within an evaluation date are
not significantly different (alpha = 0.05).

Fig. 1. Photo showing white clover control associated with postemergent application of LockUp made to moist foliage. Photo was taken 4 WAT at the 2008 Rugters Univeristy study location.

Fig. 2. Photo showing white clover control associated with postemergent application of Plus 2 made to moist foliage. Photo was taken 4 WAT at the 2008 Rutgers University study location.

Fig. 3. Photo showing white clover control associated with postemergent application of Trimec made to moist foliage. Photo was taken 4 WAT at the 2008 Rutgers University study location.

Fig. 4. Photo showing white clover population in untreated plot. Photo was taken 4 WAT at the 2008 Rutgers University study location.

Dandelion. The 4 WAT evaluations showed the highest level of control for both moisture and treatment factors (Tables 5 and 6, Fig. 5 to 8). No differences in herbicide performance were observed on dandelion, however, trends in ordering of herbicides based on averaged numerical levels of control were observed where levels of control for LockUp trended higher than those for Plus 2 or Trimec. Greater control was achieved on dandelion across herbicides when applications were made to moist foliage.

Table 5. Mean dandelion control across study sites at
various evaluation timings.

Means followed by the same letter within an evaluation
date are not significantly different (alpha = 0.05).

Table 6. Mean dandelion control across study sites at
different application foliage moistures.

Means followed by the same letter within an evaluation
date are not significantly different (alpha = 0.05).

Fig. 5. Photo showing dandelion control associated with postemergent application of LockUp made to moist foliage. Photo was taken 4 WAT at the 2007 Pennsylvania State University study location.

Fig. 6. Photo showing dandelion control associated with postemergent application of Plus 2 made to moist foliage. Photo was taken 4 WAT at the 2007 Pennsylvania State University study location.

Fig. 7. Photo showing dandelion control associated with postemergent application of Trimec made to moist foliage. Photo was taken 4 WAT at the 2007 Pennsylvania State University study location.

Fig. 8. Photo showing dandelion population in untreated plot. Photo was taken 4 WAT at the 2007 Pennsylvania State University study location.

Conclusions

Foliar moisture at the time of herbicide application improved control of dandelion and white clover. LockUp provided better control of clover than Plus 2 at all evaluation intervals and Trimec at later evalution intervals. Dandelion control was similar for all herbicides tested.

The results indicate that foliar moisture at the time of a postemergent granule application can influence control of the tested weeds. Since most commercial and consumer applications target a complex of weeds which generally includes dandelion and white clover, recommendations should suggest granule applications be made to moist weed foliage to optimize performance.

Acknowledgment

We wish to thank university researchers, Drs. Steve Hart, Shawn Askew, Dave Gardner, Gwen Stahnke, and Mr. Jeff Borger, for developing field data used in this publication.

Literature Cited

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3. Frelich, J. R., and Horn, D. P. 1989. Splitter box system for hand application of granule materials to turf. Abstract. Proc. Agron. Meeting. 157-158.

4. Gray, E., McGee, E. M., and Carlisle, D. F. 1973. Seasonal variation in flowering of common dandelion. Weed Sci. 21:230-232.

5. Hourdajian, D. 2006. Introduced species summary project dandelion (Taraxacum officinale). Invasive Biology Introduced Species Summary Project. Columbia Univ., New York, NY.

6. Jagschitz, J. A., Ebdon, J. S., Erlandsen, T., and Bylterud, A. 1983. Broadleaf weed control trials in turf in USA and Norway. Proc. Northeast Weed Sci. Soc. 37:65-70.

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8. Littell, R. C., Milliken, G. A., Stroup, W. W., and Wolfinger, R. D. 1996. SAS system for mixed models. SAS Institute Inc., Cary, NC.

9. SAS Institute Inc. 2009. JMP, version 8. SAS Institute Inc., Cary, NC.

10. Scott, D. T., and Neal, J. C. 1995. Postemergent broadleaf weed control with Confront granule fertilizer formulations. Proc. Northeast Weed Sci. Soc. 49:105-106.

11. Snider, J., Bloodworth, H., and Watson, V. 1994. Cover crop potential of white clover: Morphological characteristics and persistence of thirty-six varieties. Mississippi Agric. Forestry Exp. Serv. Res. Report 19:1-4.

12. Uva, R. H., Neal, J. C., and DiTomaso, J. M. 1997. Weeds of the Northeast. Cornell Univ. Press, Ithaca, NY.