Bitterweed is an annual wildflower from the aster family that frequently infests pastures, sandy ground, prairies and disturbed sites. The weedy plant has a mature height of ½ to 2 ½ feet and blooms with small, five to 10 petaled yellow flowers. Bitterweed gets its name from its bitter, toxic foliage that gives cow milk a bitter taste if grazed. Greater quantities of foliage ingestion can kill domesticated farm animals and horses. You can kill bitterweed in pastures with the use of 2, 4-D herbicide, as recommended by the Mississippi State University Extension.
Apply the herbicide to young, active growing weeds for best control. Younger plants are more effectively controlled than the more mature ones.
Check that the weeds have at least two true leaves before you start treatment. If the weeds do not have true leaves, the effect of the herbicide is reduced.
Mix herbicide at the rate of 1 to 2 pints for every 10 to 20 gallons of water. Fill the sprayer with herbicide solution.
Spray all weed plants evenly at the recommended rate of 20 gallons per acre. Do not use a low spray volume, as this usually does not provide coverage adequate to kill the weed.
Do not treat pastures that are severely drought stressed. Also, do not use the herbicide on pastures of annual legumes until after the production of seed.