Weed Control in Limpograss During Short Supplies of Dicamba

June, 2014
by Brent A. Sellers and Cody Lastinger, UF/IFAS, Range Cattle REC, Ona

Limpograss is a popular forage for hay production and grazing the south Florida.  Since its release in the late 1970s, dicamba (Banvel, others) has become the standard herbicide utilized for weed control.  However, with the recent 2,4-D and dicamba resistant crop varieties being developed, dicamba supplies have dwindled.  Some chemical sales representatives have mentioned that they cannot get any additional dicamba.  This is troubling, since growers and industry professionals rely so heavily on dicamba for weed control in limpograss. 

The effect of several herbicides on limpograss tolerance was examined during the 2013 summer growing season.  The experiment was initiated in July on an established limpograss hayfield.  The trial area was mowed to simulate haying at biweekly intervals and herbicides (Table 1) were applied to limpograss regrowth measuring 6, 12, 24, and 36 inches; herbicides were applied to all regrowth heights on the same day.   A non-ionic surfactant at 0.25% v/v was included with all herbicide treatments. Limpograss injury was evaluated visually at 30 days after treatment and biomass was collected 90 days after treatment. 

There was no influence of regrowth height on visual limpograss injury or biomass.  Therefore data were averaged over all regrowth heights (Table 1). Velpar at both rates, Pasturegard HL and WeedMaster resulted in at least 19% visual injury 30 days after treatment, which was significantly greater than the dicamba-treated check.  Chaparral resulted in the lowest amount of injury, but injury was not significantly different using WeedMaster, GrazonNext HL, or Metsulfuron.

Table 1. Effect of herbicides on limpograss injury 30 days after treatment and biomass 90 days after treatment. Numbers followed by the same letter within each column are not significantly different at P = 0.05.
Herbicide Rate (oz/acre) Injury (%) Biomass (lb/A)
Banvel (diacamba) 24 0 c 5,104 a
2,4-D amine 64 19 b 3,844 bc
WeedMaster 48 14 bc 4,795 ab
GrazonNext HL 24 16 bc 4,498 ab
Metsulfuron 0.3 11 bc 4,786 ab
Pasturegard HL 24 21 b 4,481 ab
Chaparral 3 8 c 5,280 a
Velpar 32 20 b 2,907 c
Velpar 64 55 a 1,394 d

WeedMaster resulted in a 25% reduction in biomass compared to dicamba-treated limpograss.  Velpar applied at 32 and 64 oz/A resulted in 43 and 73% less biomass , respectively, than when treated with dicamba. Although Pasturegard HL resulted in as much injury as 32 oz/A Velpar at 30 days after treatment,  biomass was not significantly different from dicamba-treated limpograss.  The yield reduction observed from Velpar in this study is particularly troublesome, since it is the only herbicide option we have for smutgrass control. 

Although there were numerical (non-significant) reductions in limpograss biomass from GrazonNext HL, Pasturegard HL, and WeedMaster, it is likely that the forage quality benefits of removing problematic weeds such as dogfennel will outweigh the yield loss caused by the herbicide.  Since dicamba supplies are limited, we may have to rely upon some herbicides that we know will cause low to moderate levels of limpograss injury if weeds have become problematic.  Keep in mind, also, that this is data only from one year of research.  This research is being repeated in 2014.  

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