Managing pastures and hayfields for optimum production involves forage species selection, fertility management and weed control.

Weeds that compete in forage fields can directly decrease the quantity and quality of the forage being produced. Some weeds, such as poison hemlock, jimsonweed and horsenettle, may even be poisonous because of toxic compounds in the plant.

Fortunately, livestock often overlook these poisonous plants if other readily available forage is present. But other weeds may cause bloat or nitrate poisoning in the right environmental conditions. And some plants, such as musk thistle and teasel are considered noxious weeds. They should be eliminated from the forage fields.

Weeds left alone to grow and reproduce will eventually start taking over more areas of the pasture or hay fields. These weed problems don't develop overnight and will not go away overnight. It takes dedicated effort to work on these weed problems. If using herbicides to control weeds, it is important to remember that no herbicide is 100 percent effective. Also, because of a weed's ability to reproduce, re-spraying the following year is often needed.

To control weeds it's extremely important to identify the weed and understand its life cycle. Trying to control weeds as they complete their life cycle often will not stop them from producing viable seeds.

Generally, plants are broken down as annuals, biennials and perennials.

Annual plants live one year or less and reproduce by seeds. These plants will often be considered either winter annuals or summer annuals. Winter annuals germinate in the fall, over winter, then flower, set seed and die the following spring. Examples of these weeds include chickweed, henbit, deadnettle, sheperdspurse, etc. Controlling these weeds should be done in the fall prior to the plant's over wintering or early in the spring before the plants start to flower. Winter annuals are often not a big problem in established cool-season grass forage fields, but they may be a problem if seeding cool-season grasses in the fall.

Summer annuals germinate in the spring and complete growth by the fall. Examples of these weeds include cocklebur, ragweed species (common, lanceleaf, giant), redroot pigweed, spiny amaranth, etc. Controlling these weeds should be done in the spring or early summer when the weeds are germinating and are very small. Always try to spray before flowering. Summer annuals can be major weed problems in many established pastures and hay fields. These weeds grow very well in the summer months when cool-season grasses are basically shutting down because of the heat. It is important to remember that fields that have had past problems with summer annuals need to be targeted to bring the weeds under control. Tremendous amounts of weed seed produced in one ideal growing season can create problems for years to come.

Biennials are plants that live no more than 2 years and reproduce only by seeds. These plants often germinate in the fall and for their first year grow as a rosette close to the ground. As the rosette gets bigger in the second year of its life cycle, it undergoes rapid stem elongation, flowering and then seed set. Examples of these weeds include poison hemlock, wild carrot, wild parsnip, teasel, bull thistle, musk thistle, etc. These weeds can be major problems in forage fields. Controlling these weeds should be done when the plants are germinating or while they are still in a rosette form prior to rapid stem elongation and flowering. Fall spraying can be very effective on these weed types because new plants are emerging and the 1-year-old plants are still in the rosette stage, trying to build root reserves to survive the oncoming winter. While spraying in the early spring can help control the young plants that germinated last fall, application must occur prior to the older plants switching to reproductive phase.

Perennials are plants that may live for several years, reproducing from seed and/or through roots and rhizomes. These types of plants can germinate in the fall or spring. Examples of these weeds include dock species, chicory, goldenrod, horsenettle, ironweed, sericea lespedeza, etc. These weeds can also be major problems in forage fields. Adequately controlling these weed types is difficult. The best time to control these weeds is when bud stage is initiated and the plant starts building root reserves. Spraying herbicides that translocate to the root reserves is the best control approach. Seedling plants that are in their first year of growth can be sprayed prior to bud stage.

For more information on pasture weed control, products and rates, get a copy of the 2003 MFA Agronomy Guide from your local MFA Agri Services Center. n

Some quick points to remember for weed control in pastures and hay fields.

• Identify the weed problem.
• Select the best weed control option.
• Spray at the right time with the right herbicide, the right rate. Use a calibrated sprayer.
• Recognize that drought-stressed or mature weeds will be more difficult to control.
• Follow label directions for application and mixing of the herbicide.
• Follow haying/grazing restrictions of the herbicide.
• Follow crop rotation guidelines of the herbicide.
• Understand that additional treatments may be necessary.