published in


August 2016

Broomsedge Management in Bahiagrass Pastures An Ongoing Study

Brent Sellers, Maria Silveira, and Jay Ferrell

For questions or comments regarding this publication contact: Brent Sellers, University of Florida, IFAS

Broomsedge (Andropogon) species are native, warm-season, short-lived perennial bunchgrasses with an average life span of 3 to 5 years. While some species are desirable in many natural areas and native rangeland, they are becoming problematic in improved bahiagrass pastures throughout central and south Florida. Limited research has been conducted concerning pasture management to reduce broomsedge infestations. Many extension specialists in the southeastern US indicate that soil testing followed by the appropriate amendments to increase the competitive ability of desirable species is the only way to manage broomsedge. However, with over 18 species of broomsedge present in Florida, an across the board recommendation for all species is not likely attainable. For example, bushy bluestem appears to grow better in alkaline soils (pH >7) while purple bluestem grows in more acidic soils. Therefore, liming alone may or may not result in a decrease in broomsedge density over time. Furthermore, the pH target levels for desirable grasses may not inhibit the growth of broomsedge species. Applications of phosphorus have also been suggested to decrease broomsedge invasion, but this has not been documented in Florida where subsoils are typically rich in phosphorus. However, since no herbicides can selectively remove these species, different management programs must be evaluated for their effectiveness. Therefore, our objective is to determine what soil amendments will result in a reduction broomsedge density over a 5 year period.

This research was initiated in 2012 near Ona and Arcadia, and in 2013 near St. Cloud. Treatments included a 3-way factorial of 0 or soil test recommended lime, 0 or 500 lb/A 10-5-10 fertilizer, and 0 or 25 lb/A micronutrient mix (Frit 503G). Only the Ona location required an application of lime onto half of the plots in 2012 (2 ton/A; initial soil pH = 4.3). Soil pH at the Arcadia location tested 7.7, and elemental sulfur has been applied annually at 100 lb/A in place of lime (only half of the plots received this treatment). No lime has been added to the St. Cloud location (soil pH = 5.5).  Each location is also composed of different broomsedge species, with purple bluestem at Ona, bushy bluestem at Arcadia, and broomsedge bluestem at St. Cloud.  Broomsedge density at each location has been counted annually at four geo-referenced locations within each plot so that the same area is counted.

Treatments did not result in a reduction in broomsedge densities until after 3 years of application; no change in broomsedge density has been observed at St. Cloud.  Application of lime at the Ona location increased the soil pH from 4.3 to 5.0.  Purple bluestem densities did not change in plots that received no lime, but a 43% reduction in density was observed by the addition of lime alone.  Similarly, annual applications of N-P-K has resulted in a 38% decrease in purple bluestem density over a 3 year period, but no change in density was observed without the addition of fertilizer. Sulfur application has had no impact on soil pH in Arcadia, and only annual applications of N-P-K fertilizer has resulted in a decrease in bushy bluestem density; bushy bluestem density has decreased by 77% over a three year period. However, it is important to point out that busy bluestem density has decreased at this location by 40% without any treatment (no sulfur, lime, or micronutrients). Micronutrients have shown no effect on broomsedge density at either location.

At this point in time, we do not know whether it is the N, P, or K portion of the fertilizer that is affecting broomsedge populations.  Additionally, it is too early to suggest that annual applications of N-P-K fertilizer will have long-term impacts on broomsedge densities across the state as we have not yet observed a decline in broomsedge density at the St. Cloud location. These sites will continue to be evaluated for at least two more years. Broomsedge counts for 2016 have not been recorded at the time of this publication. 

Current options to control broomsedge in pastures include spot-treatment or a wiper application using glyphosate.  For spot-treatments, a 1-2% v/v solution is usually sufficient.  A glyphosate concentration of 10% v/v has been successful at the Range Cattle Research and Education Center.  In August, 2014 glyphosate (10% v/v) was wiped onto broomsedge in two directions. Within a 2 week period, broomsedge plants began to show signs of glyphosate activity (Figure 1). Unfortunately, these pastures were mowed at this time for a grazing trial. However, by 1 year after treatment, the broomsedge population declined by approximately 70%. This pasture was wiped a second time in the fall of 2015 to control escapes from the first application.  After investigating this pasture in June, 2016, it appears that we have controlled nearly 95% of the original population (Figure 2).

Figure 1. Broomsedge response 2 weeks after wiping with a 10% v/v glyphosate solution in August, 2014. Photograph by B. Sellers. Figure 2. Response of bahiagrass pasture following two annual fall wiper applications of 10% v/v glyphosate. Approximately 95% of the broomsedge has been removed from this pasture. Photograph by B. Sellers.

Since broomsedge species are difficult to remove without spot-treatment or by using a weed wiper, it is important to limit their spread within or across pastures. If broomsedge is beginning to invade in certain areas within a pasture or has escaped a previous wiper treatment due to coverage issues, be sure to spot-treat those areas to prevent seed production as the seeds are wind-dispersed (Figure 3). Additionally, it is important to monitor soil pH to ensure that bahiagrass is growing under optimal conditions. Bahiagrass tends to take a lot of abuse because it tolerates many conditions including overgrazing, low fertility inputs, and soil moisture extremes, but too much abuse may be the underlying cause of broomsedge infestations in many areas of the state.

Figure 3. Regrowth of broomsedge plants that are growing in the fenceline of the wiped bahiagrass pasture. These plants should be spot-treated with glyphosate to prevent further seed production. Photograph by B. Sellers.

You are invited to join us by webinar on August 25, at noon, when Dr. Sellers will be presenting the information covered in this Ona Report and he will be available to answer any questions afterwards. To participate this webinar you simply need to register online here: https://attendee.gotowebinar.com/register/166012337883974404 .

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