Mowing is especially effective in reducing the amount of weed seed produced by established broadleaf weeds. The mower should cut as close to the ground as possible. Mowing may not completely eliminate weed seed production, since some seed could be produced by plants that regrow from tillers present on grasses below the height of cutting. Also, perennial weeds that spread by underground rootstocks, like thistle, are not effectively controlled by a single mowing.
Two popular types of weed control products are pre-emerge and post-emerge herbicides. Pre-emerge herbicide must be applied before the weed seeds germinate. An example of a pre-emerge product is Prowl H2O. This herbicide is used to control Crabgrass in Bermudagrass hayfields. Post-emerge products are used to kill weeds after they have germinated. These herbicides must be used when the plant is actively growing and not simply green.
Most herbicides have grazing and feeding restrictions stated on the label that limit the use of the crop for livestock feed. Producers should know and adhere to any grazing or haying restrictions.
These restrictions can be anywhere from seven days to one year. Different products vary in their restriction guidelines. Many 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.
When using any herbicide, it is important to be aware of the surrounding crops. Drift from many of these herbicides are lethal to other crops like vegetables, shrubs and flowers. Pesticide spray drift is the movement of pesticide dust or droplets through the air at the time of application or soon after, to any site other than the area intended. They should choose a product that will not harm surrounding crops if drift occurs. Drift will vary with boom height, nozzle type, pressure, and wind.
Another control method includes various herbicides that are available to provide broad-spectrum weed control. When making your selection try to choose a product that will control as many weeds as possible. This reduces the use of herbicides and also minimizes cost by reducing the number of passes through the field. When applying multiple products choose products that can be mixed in the same tank and applied in one pass.
Proper integration of many practices, including stocking rate, grazing rotation and duration, and the rate and timing of fertilizer and herbicide applications, are critical for holding weeds at bay. Keeping a desirable forage base that is dense and competitive helps hold out these invaders and extends weed control. Going back to a grazing system that encourages heavy patch grazing and little to no rest will result in a reinfestation within a year or less.
If possible, foliar- or basal-treat trees and brush and allow them to stand for at least 60 days during the growing season before cutting. This will give the herbicide time to move throughout all parts of the plant. For foliar treatments, make sure leaves of target brush have fully expanded to maximize exposure to the herbicide. Treating leaves that are not fully expanded often will not allow sufficient transport of herbicide to the root system and result in poor control.
“Mowing is a cheap way to control weeds,” is one often heard statement. Factoring in time, along with fuel, maintenance, depreciation, and storage of equipment, most ag economists will place a minimum cost of $15 per acre on mowing. That’s really not cheap, especially when the results may only last a few weeks.
Most producers recognize the negative impacts of weeds on forage production and seek to control these invaders. However, several of the methods used for control lack effectiveness. After years of working to solve many of the pasture weed and brush issues that producers face, my colleagues and I have noted a few questionable beliefs and practices that continue to be employed.
We also have to address the issue of why animals choose not to eat certain weeds. Not all plants in the pasture are edible, and the case for grazing them ignores the presence of poisonous plants or those that can cause serious physical damage to the animal. Carolina horsenettle, for example, can be toxic if too much is grazed. Even if grazed under that limit, the horsenettle spines irritate the mouth and esophagus, creating discomfort and reducing forage intake and performance.
It’s not that mowing can’t control weeds; it’s that the number of mowings and the timeliness of each mowing are critical for long-term control. Effective programs require mowing two to three times each season over two or more years, preventing seed production and exhausting plant energy reserves. If we use the $15 per acre minimum, we’ve spent $60 to $90 per acre for weed control.