Pasture Herbicide Update

by Dr. Brent Sellers, University of Florida/IFAS

published in The Florida Cattleman and Livestock Journal

Over the past several years, we have seen advances in the herbicide market for pasture weed control. In fact, things have changed dramatically since tropical soda apple first invaded pastures in south Florida. So, if you’re looking for the silver lining, the invasion of tropical soda apple has actually increased our herbicide options for weed control in pastures. In 2012, and even in late 2011, there are several changes that should be acknowledged.

Velpar. Hopefully, most are aware of the label change this past year. There are no grazing restrictions when applying less than 4.5 pt/A. The haying restriction for Velpar is 38 days when applying less than 4.5 pt/A. Since most of our applications for smutgrass control do not typically exceed 4 pt/A, most should be able to graze pastures immediately after grazing. Be sure that Velpar is only applied during the rainy season as root uptake is essential for smutgrass control.

GrazonNext HL. Dow AgroSciences has recently changed the formulation of GrazonNext to GrazonNext HL by adding more active ingredient per gallon of product. In this case, HL stands for “high-load” or a more concentrated product. In doing this, the rate structure per acre has changed. We have tested this formulation and it appears to provide identical levels of weed control compared to the traditional GrazonNext formulation. Table 1 outlines the new rate structures and other important information.

Be aware that aminopyralid, one active ingredient in GrazonNext and GrazonNext HL, is a potent herbicide that remains herbicidally active in manure after animals have consumed treated plants. Therefore, mulching or fertilizing with this manure can be highly injurious to sensitive plants such as tomato, pepper, and other vegetable crops. For this reason, Dow AgroSciences has instituted a number of restrictions about moving treated hay, silage, etc. off the farm or ranch. Fortunately, Florida currently possesses a supplemental label allowing the transfer of treated hay off the farm/ranch, but it is important to be aware of the possibility of injury to non-target plants. For more information on the supplemental label, consult your county extension agent.

Pasturegard HL. Pasturegard has also been reformulated to a “high-load” formulation by Dow AgroSciences. Table 2 summarizes the difference in the old formulation and the new PastureGard HL formulation. Note that the grazing and haying restrictions have remained the same.

Outrider. Monsanto has expanded, through supplemental labeling, the use of Outrider herbicide. Previously, it could only be applied in established bermudagrass and bahiagrass. As with the new labels, it can now be applied to established limpograss (Hemarthria) and stargrass. It can also be used as a rescue treatment while establishing bermudagrass, limpograss and stargrass as long as it has been planted for 30 days. The standard use rate is 1.33 oz/A.

Others. DuPont is currently in the process of registering several products containing a new active ingredient, aminocyclopyrachlor. The names and use rates of these new products are not clear at this time, but we expect to have this information sometime in late 2012. We will provide you with updates on these products as we become aware of them.