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.

Step 1

Apply the herbicide to young, active growing weeds for best control. Younger plants are more effectively controlled than the more mature ones.

Step 2

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.

Step 3

Mix herbicide at the rate of 1 to 2 pints for every 10 to 20 gallons of water. Fill the sprayer with herbicide solution.

Step 4

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.

Step 5

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.