Get After the Weeds Yet This Fall

Mark Landefeld, Extension Educator, Monroe County (originally published in The Ohio Cattleman)

Left: no herbicide, Right: dicamba. Label requires livestock be removed from treated fields at least 30 days before slaughter. No waiting period between application and grazing for non-lactating animals. Don’t graze lactating dairy animals for 7 to 60 days after application, depending upon rate applied. Always read herbicide labels for restrictions.

You may not want to put the sprayer away for winter just yet. Weeds can be a problem that reduce quality, quantity and stand life of our forages. We generally think of battling weeds in the spring or early summer, as crops begin to grow, because we naturally want to reduce competition for our forage crops. However, the best time to control many winter annuals, biennials and cool season perennial weeds is mid/late-September through early November.

Highly productive pastures and hay fields do not happen just by accident. Good grazing management, weed and pest control, nutrient management and properly timed harvests all have an important role. Weeds often reduce the palatability of forages and certain weed species are potentially poisonous to grazing livestock making plant identification even more important.

The Ohio State University Extension Weed Control Guide (Bulletin 789) suggests the best way to control weeds in established stands of alfalfa is to maintain a dense healthy forage stand through proper fertilization, cutting management, and insect control. More than 95% of the weeds can be controlled through good management practices.

However, weeds can cause problems. Some alfalfa stands have been reported to lose up to 30% of the stand from infestations of common chickweed. If chickweed emerges through the fall and into spring it develops a thick lush mat that competes strongly with the alfalfa until first cutting hay is made. Purple deadnettle and henbit can cause the same problem. If these weeds persist and then die, summer annual weeds like foxtails, lambsquarter, pigweed or others often take over. Perennial weeds such as dandelion or Canada thistle can also creep into portions of the growing area to reduce yields and/or quality even further.

In many cases, herbicides can be used to eliminate weed pressure in alfalfa stands if you choose to do so, but always read the label. Kerb herbicide can be used to control certain weeds in established or new plantings after the legume has reached the trifoliate leaf stage but only in the fall before soils freeze. Products that can be applied to established, dormant alfalfa (at least one year old) include metribuzin (Sencor or Lexone), Velpar, or Sinbar.  However, before using herbicides, one should evaluate the existing stand to be sure it is worth the cost of the herbicide and the expense to apply the treatment. Renovation and reseeding may be more cost effective.

When weeds invade mixed legume/grass stands it poses a little different problem than pure stands because herbicide management strategies are limited that remove broadleaf weeds without killing your legumes. Grazing management and harvest management provide help here if you do not allow weeds to mature to the stage of viable seed production, but this is extremely hard to accomplish. So, spending money to provide good fertility may be the best and most cost effective means to reduce weed pressure in mixed grass/legume stands. Good soil fertility and maintaining soil pH of 6.5-7 helps forage plants vigorously compete against weeds. It is also critical, in fields used for hay and grazing, that livestock are not allowed to overgraze forage plants. This can cause the desirable plant’s root reserves to be used and weeds quickly take the opportunity to start growing.

Pastures also have weed problems and timely mowing can be beneficial to keep setting weeds back. Invasive plants, such as spotted knapweed or thistle, herbaceous weeds like ironweed, horsenettle and cocklebur try to take over pastures, leaving producers few alternatives but to use herbicides. Some herbicides however, work more effectively than others do on given weeds and timing of sprays can be critical. Therefore, it is necessary to identify the target weeds so proper herbicide(s) are used. Numerous products and those that contain 2,4-D in combination with herbicides such as dicamba (Brash, Latigo, Outlaw, Weedmaster),  aminopyralid (GrazonNext HL), triclopyr (Crossbow, Crossroad, Candor), or the metsulfuron products can be used to kill broadleaf weeds. If legumes such as clover are present in pastures, they can be severely injured or killed by these herbicide products, but legumes can be reintroduced after a period of time. Grazing restrictions and legume reseeding intervals vary with each product, so always read the label carefully when planning to use herbicides.

Fall can be a good time to eliminate or reduce a variety of weeds. Proper recognition and prompt action to control these invaders is important. Eliminating weeds while they are small and few in number will save you a lot of headaches later. So, be aware, monitor your fields, identify weeds in your hay and pasture fields and deal with them in a timely manner.