THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL
Is Metsulfuron an Option for Blackberry Control in Bahiagrass Pastures?
Dr. Brent Sellers
Metsulfuron is a highly effective herbicide that has been labeled for use in bermudagrass and stargrass pastures for many years. The favorable characteristics of metsulfuron (non-volatile, non-staining, low odor) and its weed control spectrum has led many manufacturers to market metsulfuron alone (MSM 60, Clean Pasture, etc.) as well as in combination with many other herbicides: Cimarron Plus and Cimarron X-tra (metsulfuron + chlorsulfuron), Chaparral (metsulfuron + aminopyralid), Pastora (metsulfuron + nicosulfuron) and others. Of particular interest is the activity of metsulfuron on blackberry. Our research has shown that blackberry control with metsulfuron is usually more consistent and effective than that observed following a triclopyr (Remedy Ultra) application (Figure 1). However, since the majority of blackberry is present in bahiagrass pastures, the use of metsulfuron for blackberry control has not been a general recommendation.
Figure 1. Influence of application timing on blackberry control with Pasturegard (4 pt/A), Remedy (2 pt/A) and metsulfuron (0.3 oz/A) two years after treatment. Error bars denote 95% confidence intervals.
Bahiagrass cultivars respond differently to metsulfuron application. For example, ‘Argentine’, ‘Paraguay’ and ‘Common’ bahiagrass cultivars are fairly tolerant to metsulfuron, while ‘Pensacola’, ‘Tifton-9’ and ‘Riata’ can be severely injured when metsulfuron is applied to actively growing plants. Considering that the majority of bahigrass grown in Florida is ‘Pensacola’, one might suggest that the use of metsulfuron for blackberry control would not be possible. However, application timing and/or the addition of a 2,4-D-containing herbicide appears to influence the level of injury metsulfuron on bahiagrass (Table 1). Note that the addition of 2,4-D amine to 2.0 oz/acre Chaparral and WeedMaster to 0.3 oz/acre of MSM 60 resulted in a dramatic decrease in bahiagrass control 60 days after treatment.
Table 1. Influence of metsulfuron-containing herbicides and tank-mixes on ‘Pensacola’ bahiagrass control (visual estimates).
In 2009, we began researching the effects of metsulfuron on bahiagrass yield. We specifically wanted to determine if we could overcome the negative effects of metsulfuron on ‘Pensacola’ bahiagrass by tank-mixing with 2,4-D amine. We applied metsulfuron at 0.3 and 0.5 oz/acre with and without 1 pt/acre 2,4-D amine during the early spring and late fall to a pure bahiagrass stand; a time when herbicide applications for blackberry control are recommended.
When 2,4-D was applied with metsulfuron reduced herbicidal activity was observed on the bahiagrass, but only when 0.5 oz/acre was applied in the spring and when 0.3 oz/acre was applied in the fall (Figure 2). Bahiagrass yield following 0.3 oz/acre metsulfuron with 2,4-D amine was not different from that in the untreated check when applied in the fall; this is the same application rate used for blackberry control shown in Figure 1. Although it appears that 2,4-D reduces the injury associated with metsulfuron in the spring, injury tends to be less severe when applied in the fall.
Figure 2. Impact of application timing on bahiagrass yield. Data from the spring application includes the cumulative yield of two harvests, while data from the fall application only includes yields from one harvest when bahiagrass was 12 inches tall in the untreated check.
The question remains, should metsulfuron be used to control blackberry in bahiagrass pastures? Let’s consider two things: 1) dense infestations of blackberry often limit the amount of grazing in infested areas; therefore the bahiagrass that is present is essentially avoided, and 2) metsulfuron rarely results in complete bahiagrass death under Florida conditions with or without 2,4-D amine. It appears that metsulfuron-containing herbicides are valid treatment options for blackberry in heavily infested pastures, but tank-mixing 2,4-D amine or a product containing 2,4-D would definitely limit the amount of bahiagrass injury associated with metsulfuron. However, this treatment should only be applied in dense blackberry stands where severe bahiagrass injury can be tolerated for 4 to 8 weeks.