Even though the drought has limited some broadleaf weed applications this month, we are now in the prime season for broadleaf weed control. Actually there is plenty of time left for good control. 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. 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 with lower activity on ground ivy were most effective from Oct 1 through Nov 1, and efficacy decreased outside of this window. 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.
