Spray volumes for pasture areas should be 20 to 30 gallons per acre with ground sprayers. Lower volumes also will work, but risk of spray drift increases. Aerial application of lower volumes also may be used.
Musk and curled thistles are major problems in western Virginia and Maryland and continue to spread eastward. These plants are considered biennials, but some plants actually may germinate in the spring and flower in the late summer. Such plants would be annuals. In the spring, susceptible crop and ornamental plants are actively growing and will be damaged if spray drift reaches them.
The 2,4-D used for thistle control has little residual activity in the soil. Weeds reinfest areas where thistles are killed in the fall. This results in plants that bloom and produce seed the next summer. Based on this, spring may be the best time to control thistles. At the same time, controlling thistles in the spring is hazardous to the growth of desirable plants.
Rates of application are stated in pounds of acid equivalent (AE) per acre. Amine, low-volatile ester (LVE), and oil-soluble amine (OSA) formulations for various weed situations are suggested. Various formulations containing from 2 to 6 pounds acid equivalent per gallon are available. Usually, higher acid equivalents per gallon are more economical. The following table will aid in converting pounds per acre to liquid volumes necessary to supply the amount of the weed killer suggested. It is important to have the correct amount of herbicide.
| Pints of given formulation necessary to supply the following rates per acre | ||||||
|---|---|---|---|---|---|---|
| AE (lb/gal on label) | 1/4 lb | 1/2 lb | 1 lb | 2 lb | 3 lb | 4 lb |
| 2 | 1 | 2 | 4 | 8 | 12 | 16 |
| 3 | 2/3 | 1 1/3 | 2 2/3 | 5 1/3 | 8 | 10 2/3 |
| 4 | 1/2 | 1 | 2 | 4 | 6 | 8 |
| 6 | 1/3 | 2/3 | 1 1/3 | 2 2/3 | 4 | 5 1/3 |
