Pastora Herbicide: A New Tool for Grass Weed Control in Bermudagrass

by Dr. Brent Sellers, University of Florida/IFAS

published in The Florida Cattleman and Livestock Journal

A new herbicide mixture was recently labeled for use in established bermudagrass pastures and hayfields for control of weedy grasses. Pastora is a premix of nicosulfuron (56.2%) and metsulfuron (15%). Though metsulfuron has been used for many years in pastures, nicosulfuron is new to this market and provides new opportunities for weed control. The use rate for Pastora is 1.0 to 1.5 oz/acre per application, with a total maximum of 2.5 oz/acre/year. The amount of metsulfuron in 1.0 and 1.5 oz/acre of Pastora is equivalent to applying 0.24 or 0.37 oz/acre of any 60DF formulation of metsulfuron (MSM60, Accurate, Clean Pasture, etc). Though this rate of metusulfuron may not be sufficient to control blackberry or other woody perennials, it will provide superior control of many annual weeds (red sorrel, Carolina geranium, henbit, and others). There are no grazing or haying restrictions when using Pastora. 

The primary target weed for this herbicide has been sandbur, but Pastora will also control many other grass weeds including barnyardgrass, coast cockspur, johnsongrass, vaseygrass, seedling crabgrass, and several others. In addition to grass weeds, several winter and summer annual broadleaf weeds can be controlled with this herbicide. Dogfennel and tropical soda apple will not be controlled with this product. 

For optimum control of grasses, it is essential to apply Pastora when weeds are small. Sandbur should be approximately 2 inches tall for consistent and complete control. Although preliminary data suggests that1.5 oz/acre will control larger sandbur, it is likely that larger plants will be stunted and seedheads aborted, but not necessarily killed. 

Tall, dense stands of bermudagrass will intercept much of the herbicide spray. Therefore, Pastora should be applied for annual grass weed control when bermudgrass is no taller than 4 inches following initial greenup or after cutting for hay. Considering that rainfall is usually limited after initial greenup, applications may need to be delayed for optimum control until after the initial hay cutting and when rainfall is sufficient for active weed growth. 

Vasseygrass is a tall-growing weed that is common on seasonally wet pastures. This weed is very difficult to control, but Pastora holds promise to reduce the influence of this weed species. Data collected within Florida suggests that Pastora will provide between 65 and 80% control of vasseygrass. These applications were made during bermudagrass greenup when rainfall is generally limited. We anticipate slightly better control of vaseygrass after full greenup, but applications will need to be made fairly quickly or vaseygrass will become too large to adequately control. 

Some intial injury on bermudagrass should be expected, but the level of injury is much less than when Journey (imazapic + glyphosate) is utilized for sandbur or vaseygrass control. Injury will consist of some bermudagrass yellowing. More severe yellowing and some biomass reductions should be expected when using higher rates of Pastora. Applications of liquid nitrogen with Pastora are allowed, and this addition to the spray mixture has resulted in less injury than with Pastora alone in our preliminary experiments. However, it is possible that applications with nitrogen fertilizer could reduce the activity on certain grass species including bahiagrass. 


Figure 1. Vaseygrass is a common perennial grass weed in bermudagrass hayfields.
Untreated vaseygrass (A) compared with control of vaseygrass 30 days after treatment with 1.3 oz/acre of Pastora herbicide (B).