There appears to be some confusion when it comes to weed control in limpograss. First, there are several names used for limpograss, including Hemarthria, limpograss, Floralta, and, more recently, Gibtuck and Kenhy. While none of these is incorrect, it is a common misconception that these names refer to different forages. It is not necessary to call limpograss by a certain name; it is only important to realize that all three names refer to the same forage grass. Secondly, new herbicides have recently been introduced into the pasture market, and the safety of these herbicides on limpograss depends on both the time of year and stage of growth. This publication is intended to help UF/IFAS Extension agents and producers reduce the amount of confusion in the herbicide recommendations for weed control in limpograss pastures and hayfields.
Weed Control at Establishment
There are only three herbicides that can be used for weed control at establishment. The most troublesome weeds during the establishment period are the annual and perennial sedges (commonly called watergrass, etc.). The most effective and safe herbicide treatment for control of sedges is 1.5–2 pt/acre dicamba (Banvel, etc.) applied 7–10 days after planting. If this 7–10-day window after planting is missed, Outrider at 1–1.33 oz/acre can be applied 4 weeks after emergence. If tropical soda apple is an issue in newly planted limpograss, apply Milestone at 3 oz/acre. Applying 2,4-D, or products that contain 2,4-D, is not recommended for newly established limpograss because it may cause substantial injury and lengthen the amount of time before the pasture is fully established.
Weed Control in Established Limpograss
Dicamba has been the long-standing standard herbicide for weed control in limpograss. Because 2,4-D and other commonly used herbicides were tested at establishment, it was believed that these products would kill limpograss. However, many of the herbicides available in the pasture market can be used for weed control in limpograss, but application timing becomes a factor. In general, 2,4-D, or products containing 2,4-D, should not be applied between April and November unless injury can be tolerated. Below are the most commonly recommended herbicides for use in limpograss for weed control including information on limpograss tolerance.
Dicamba (Banvel, etc.)
This is the standard herbicide for weed control in limpograss pastures. The advantages of dicamba include good weed control and good forage safety regardless of application timing. Most weeds are controlled with 2 pt/acre, but 3 pt/acre may be needed for larger dogfennel. If dogfennel is larger than 3 feet tall, dicamba will not provide adequate control.
Milestone (aminopyralid)
Milestone can be used year-round on limpograss but is recommended only when tropical soda apple has become a problem in limpograss pastures. Use 3 oz/acre at establishment and 5 oz/acre in established limpograss. The low recommended rate for tropical soda apple control at establishment is related to the size of tropical soda apple plants; small plants require less herbicide for effective control.
2,4-D (Weedar, 2,4-D Amine, etc.)
This herbicide has received a lot of negative attention with regards to its use in limpograss. In the past, it was thought that 2,4-D would kill limpograss. The only time that 2,4-D kills limpograss is when it is applied during the establishment period. There is a time period, however, when 2,4-D can cause severe injury of established limpograss. During the summer growing season when temperatures and relative humidity are high, 2,4-D amine almost always causes severe injury. Additionally, fertilizing limpograss prior to 2,4-D application results in injury to lush, new growth. Regrowth does occur, but it takes some time. If this herbicide is applied during the cooler seasons (November through April), the amount of injury observed in limpograss is greatly reduced. Our research has shown that 4 pt/acre of 2,4-D in the early spring results in little to no limpograss injury.
GrazonNext HL (aminopyralid + 2,4-D)
Since this herbicide contains 2,4-D, some caution is required when using this product for weed control in limpograss. GrazonNext can be safely applied to limpograss from November through April. May through October applications may result in severe limpograss injury.
DuraCor (aminopyralid + florpyrauxifen)
DuraCor is one of the newest herbicides available in the pasture market with a use rate of 12 to 20 oz/acre. The label for this herbicide allows the use of methylated seed oil (MSO) or non-ionic surfactant (NIS). Our research has shown that the use of MSO in limpograss tends to result in greater injury than when using NIS. However, the injury is fairly minimal and typically isn’t long-term.
Chaparral (aminopyralid + metsulfuron)
The application rates for this herbicide range from 2.0 to 3.3 oz/acre. Good control of winter annual weeds and thistles can be achieved at a rate of 2.0 oz/acre. Bahiagrass can be suppressed with this herbicide when applied at 3.0 oz/acre during the summer rainy season. The drawback to Chaparral is that it will not provide control of dogfennel, but expect good to excellent control of tropical soda apple, pigweed, and blackberry. We have not examined the limpograss tolerances of this herbicide during the summer growing season. As a result, caution should be exercised when using this product for weed control in limpograss.
Outrider (sulfosulfuron)
Outrider can be used in established limpograss to control sedges at 1–1.33 oz/acre. Use the higher rate for more mature stands of sedge species. This herbicide can be applied at any time without concern for forage injury.
Pasturegard HL (fluroxypyr + triclopyr)
This herbicide is a common tank-mix partner with GraonNext HL to increase dogfennel control. Substantial injury can occur when applied during the summer months resulting in approximately 30% yield loss. Therefore it is best to apply Pasturegard HL with GrazonNext HL from November through April. Summer applications may be warranted when limpograss pastures are severely infested with dogfennel.
Herbicide tolerance in limpograss is tricky, but the easiest way to remember when herbicides can be safely applied in limpograss is to stop using products containing 2,4-D, triclopyr, or fluroxypyr after Tax Day (April 15). If herbicides other than Banvel, Chaparral, or Milestone are applied after Tax Day, the chance of herbicide injury in limpograss increases dramatically. Applications of herbicides containing 2,4-D can resume with reductions in limpograss injury as early as November. Table 1 illustrates when herbicides can be used for weed control in limpograss in most years; however, once limpograss enters into rapid growth, care should be exercised when choosing herbicides.
The key to determining limpograss response to herbicides is to understand the maturity and health of the stand. A newly established pasture will not have a well-established root system or the energy reserves to overcome the stress of an herbicide application. As a result, a new stand is more susceptible to herbicides than mature stands. Similarly, if an established limpograss pasture was recently grazed or cut for hay and the regrowth is lush and tender, some herbicide injury should be expected. This is because the pasture is under tremendous stress as it attempts to regrow, and the added stress of an herbicide application is simply too much to handle. As a rule of thumb, a stand that is at least 6-weeks-old (6 weeks since last graze or cutting) will show minimal injury since the plant has had sufficient time to reestablish its energy reserves.
Traditionally we have been "locked in" to using very few herbicides since it was thought that almost all pasture herbicides were too injurious to limpograss. This is simply not the case. There are many excellent herbicide choices; some simply require extra attention to the environmental conditions and health of the pasture. If the concepts discussed in this article are considered and given due attention, weed control can greatly improve along with the quality of grazed and stored limpograss with minimal injury.