Weed control in pastures and hay fields

North Carolina State University Extension, 05/13/2013

Now that summer is upon us and some dry days have arrived, producers have started making hay.  With this increase in activity, I have received quite a few calls regarding weed control in hay fields.  First of all, a weed is defined as any plant growing where you don’t want it.  So we aren’t just talking about what we commonly think of as weeds.  We are also including grass species other than the one we are cultivating, i.e. Bahiagrass in a bermudagrass field.   Everyone recognizes the need for weed control.  Not only does it make for better quality hay but it also eliminates competition from the weeds, which allows the grass to fully utilize available moisture and nutrients and reach maximum yield potential.  Here are some things to keep in mind when trying to control weeds.

There are many products on the market that will do a fine job of controlling broadleaf weeds.  Probably the most well know product is 2,4-D.  It gives excellent control of bitter sneeze weed, plantains, buttercup, and ragweed but relatively poor control of horsenettle and most woody weeds.  One note here on 2,4-D.  When applied at lower rates, it will not harm white clover.  Cimmaron is widely used.  This product is excellent on bahiagrass, curly dock, buttercup, wild garlic, and spiny amaranth.  However, it only injures ryegrass and is poor on horsenettle.  Weedmaster provides excellent control of broadleaf weeds and is the preferred product in hay operations.  Try to choose a product that will control as many of the weeds that you have as possible.  This will keep costs down and avoid multiple trips through the field.  If more than one product must be used, try to choose products that can be mixed in the same tank and applied in one pass.  Some products, like Weedmaster, can be mixed with liquid fertilizer as the carrier.  Using this method, a producer could perform two functions with one pass.

Also note the surrounding crops.  Many of these herbicides are lethal to cotton, tobacco, and soybeans.  Producers should choose a product that won’t harm surrounding crops if exposed to drift.  If this is not possible, try to choose a formulation that is less prone to volatilization.  The more volatile a product is, the more likely you will experience product drift.   Drift will also vary with boom height, nozzle type, pressure, and wind.  Remedy, Crossbow, and Redeem R&P are all labeled for hay and pasture but must be used cautiously due to drift dangers.  Grazon P&D is probably the best and most dangerous product available.  The product has seen drift up to 2000 feet.

Producers should know and adhere to any grazing or haying restrictions.  Some products have restrictions on grazing and haying.  Others have restrictions just on haying.  These restrictions can be anywhere from seven days to one year, so make sure you know what you are dealing with. An interesting note here is that most products that have no grazing restrictions for beef cattle will have grazing restrictions for dairy cattle.  Most will also have a withdrawal period before slaughter.

Controlling grass weeds in pastures and hay fields is much more challenging.  Most products on the market give minimal control on most grasses.  Cimmaron will control bahiagrass along with certain broadleaf weeds.  The ester formulation of 2,4-D will control crabgrass in newly sprigged bermudagrass for approximately three weeks.  Roundup Ultra can be used to control crabgrass and sandbur if used immediately after the first cutting.  Gramoxone Extra can be used to kill winter annuals in dormant bermudagrass and is safer on greening-up bermudagrass than Roundup.  For control during the summer growing season, the options available are Panoramic and Pastora.

Panoramic is labeled for use in bermudagrass for the control or suppression of many grass weeds.  These weeds include crabgrass, nutsedge, sandbur, Johnsongrass, vaseygrass, barnyardgrass, and others.  It will cause stunting of the bermudagrass, especially if used at high rates.  For this reason, Panoramic should not be used until the bermudagrass has reached full green-up. No more than 6 ounces per acre of the active ingredient, imzapic, should be applied, regardless of the weed species you are trying to control.  At this rate you will see minimal and acceptable levels of suppression to the bermudagrass.  If more than 6 ounces are used, be prepared for severe, very noticeable suppression of the bermudagrass crop.  Also note that this herbicide has a lenghty restriction on overseeding rye.  This will limit the use of these two products on sprayfields that will be overseeded.  In these cases, control of problem grasses can come from the use of spot treating with Roundup, application of Roundup with a wicking device, or Pastora.

Pastora is being widely used in this area.  Patora is labeled for bermudagrass pastures and hay fields and has no grazing or haying restrictions.  Moreover, it will not cause sever stunting of bermudagrass like Journey or Panoramic except when liquid nitrogen is used as the carrier.  Pastora will control twenty-five different grass weeds and over 100 different broadleaf weeds.  In field trials, it has been excellent in controlling crabgrass, vaserygrass, and johnsongrass.  It will also control sand spurs.

One issue that should be addressed here is the use of MSMA, monosodium methanearsenate, on pastures and hay fields.  This product will give post emergent control of crabgrass, dallisgrass, goosegrass, bahiagrass, netsedge, and sandbur.  However, it is NOT labeled for use in forages.  The “A” in MSMS stands for arsenate, which is a derivative of arsenic.  The use of this product causes a buildup of arsenicals in the plants, which can lead to poisoning of livestock that graze the forage or are fed the hay from treated fields.  Horses are most sensitive followed by cattle, sheep, and goats.  There are documented cases of cattle deaths due to arsenic based herbicide applications.  This product should not be considered an option in weed control for forages.  Alternative chemicals and/or application methods should be used.

Source: Paul Gonzalez

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