To effectively control weeds in pastures, we should examine how the weeds got there in the first place.
In a new seeding, it is extremely important to start with weed free seed and control weeds until the forages can get established. In established pastures, often weed problems are a result of overgrazing.
To combat weeds in our pastures the first place to start is taking a soil sample to determine the fertility of the field.
Some weeds, such as broomsedge or poverty grass, grow very well in acidic soils with low nutrient levels and are drought tolerant. Once pH and nutrient levels are corrected, then you can start to develop a grazing management plan and weed control options.
The second step is to determine what weeds you have. Weeds can be categorized into three types: annuals, biennials and perennials. Annuals can be further divided into summer annuals or winter annuals.
Summer annuals germinate in the spring or summer, flower, set seed and die in a single growing season. Winter annuals germinate in late summer to early spring, produce seeds in mid to late spring and then die. Winter annuals typically do not thrive in hot, dry conditions.
Annual weeds can be effectively controlled by mowing prior to flowering or with a spring herbicide treatment.
Biennials require two years to complete their life cycles and perennials generally live for more than two years. Timely mowing by itself will take several years to control many perennial weeds.
Herbicide treatments are most effective on perennials and some biennials when the plants are in the bud to bloom stage or early fall. These weeds are typically the most problematic in pastures and hay fields.
Once the weed has been identified, we can then ask ourselves if we really need to do anything. There are many reasons for controlling weeds.
For some, it might simply be for aesthetics, but for most, it is to improve forage quality and quantity. Although, some weeds do have some relatively good feed values, especially the grassy weeds during the early vegetative stage.
However, most of our problem weeds are unpalatable to livestock and are not consumed. This then leads to increased weed pressure if no control measures are taken. This is especially true for some of our poisonous weeds.
The potential for livestock poisoning depends upon how many plants are in the field, stage of growth, time of year and species of livestock. More often poisoning occurs in drought years when other forages are limited.
If you use herbicides, always read the label. For herbicide recommendations, you can consult the 2017 Weed Control Guide for Ohio, Indiana and Illinois, which is available at county extension offices and can be downloaded as a PDF online. Other states also have agronomy guides that are updated yearly.
These guides are excellent resources with herbicide response rates for each herbicide and individual weeds.
They also contain additional information on grazing or harvesting restrictions, slaughter withdrawal times, application rates, and control options for problem weeds.
Effectively controlling weeds in pastures can be accomplished with cultural or proper soil fertility, mechanical, chemical and possibly biological measures to maintain highly productive forages along with animal performance.
Good pasture management and integrating several control strategies will be more successful than relying on one single method.