With the incessant rain and high winds, most applications of broadleaf herbicides have been delayed. The good news is its not too late to apply. Nebraska research reported in 2002 showed 2,4-D and/or dicamba were far more effective in controlling dandelions and Canada thistle when applied 1 to 10 days after the first fall frost than when applied 5 to 11 days before the frost (See the Aug 9, 2004 Turf Tip). Earlier work by Bruce Branham at Michigan State showed that even though early September applications were effective in controlling broadleaves yet that same fall, Sept applications were less effective long-term than applications made in October and November (Figure 1). Our more recent work on ground ivy shows that herbicides like triclopyr (Turflon) that are very effective on ground ivy, retain their effectiveness when applied as late as early- to mid-November (Figure 2). However, herbicides that were less effective on ground ivy were most effective from Oct 1 through Nov 1, and efficacy decreased outside of this window. (Even though we have found 2,4-D to be effective on ground ivy, the ground ivy in this study is likely somewhat 2-4,D tolerant. Thus the Speedzone treatments with 2,4-D as the main active ingredient for ground ivy may be at a disadvantage in this research). The take home message is broadleaf applications should be effective when made into the first week or two of November, but control may not be seen until spring. However, herbicides that contain carfentrazone (FMC’s Quicksilver, PBI Gordons’ Powerzone and Speedzone) will still give a response in 7 to 10 days even when applied in late October or early November.
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| Figure 1. Effect of fall timing of broadleaf herbicides on control rated in Nov after application and again the following May. Note how Sep 24 applications were most effective when rated the following November, but later applications were more effective when rated the following spring (Michigan State 1986). |
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| Figure 2. Effect of herbicides applied fall of 2003 on ground ivy control measured in June 2004. Turflon (triclopyr) or Vista (fluroxpyr) retained effectiveness regardless of application date, whereas the efficacy of the 2,4-D based carfentrazone suffered outside of Oct- through Nov 1. This stand of ground ivy in this study was likely marginally 2,4-D tolerant. This research was done in 2003-2004 and has been repeated every year since then with similar results (Purdue 2004). |