General Information


638 is a special formulation containing 2,4-D acid. It is more effective than 2,4-D amines for controlling hard-to-kill weeds such as field bindweed, Russian knapweed, Canada thistle, leafy spurge, cattails, tules and nutgrass. 638 should be applied when daytime temperatures are lower than 80 to 85 degrees. Spraying when temperatures are higher may cause rapid foliar burn and decrease the product’s effectiveness. Treatment at higher temperatures also increases the possibility of crop injury. INJURY TO CROPS FROM THIS HERBICIDE MAY OCCUR. IF YOU ARE NOT PREPARED TO ACCEPT SOME DEGREE OF CROP INJURY, DO NOT USE THIS PRODUCT. Crop varieties vary in response to 2,4-D and some are easily injured. Apply 638 only to varieties known to be tolerant to 2,4-D. If you are uncertain concerning tolerant varieties or local use situations that may affect crop tolerance to 2,4-D, consult your seed company or state Agricultural Extension Service for advice.


Do not apply product through any type of irrigation system. Do not use in or near a greenhouse.

Limitations, Restrictions, and Exceptions


- Use the lower rate when weeds are small (2 to 3 inches tall) and growing actively. Use the higher rate on older and drought-stressed plants, except as directed in the SPECIAL WEED PROBLEMS section of the label.

- Beggarticks, common broomweed, knotweed, mallow (venice or little), musk thistle, prickly lettuce, Russian thistle, salsify (western or common), smartweeds (annual species), vervains, : These species may require repeat applications and/or use of higher rate recommended on this product label even under ideal conditions for application.

- Pigweeds (Amaranthus spp.): Control of pigweeds in the High Plains area of Texas and Oklahoma may not be satisfactory with this product.

Restrictions and limitations for use on cotton stubble:

- A minimum spray volume of 5 gallons per acre by air or 10-15 gallons per acre by ground is recommended.

- Do not graze dairy animals on treated areas with 7 days after application.

- Do not graze meat animals on treated areas within 3 days before slaughter.

- Do not cut treated grass for hay within 30 days of application.

Within 29 days following an application of this product, plant only those crops named as use sites on the label or other registered 2,4-D labels. Follow more specific limitations, if any, provided in the directions for individual crops. Labeled crops may be at risk for crop injury or loss when planted soon after application, especially in the first 14 days. All other crops may be planted 30 or more days following an application without concern for illegal residues in the planted crop. However, under certain conditions, there may be risk of injury to susceptible crops.

Under normal conditions, any crop may be planted without risk of injury if at least 90 days of soil temperatures above freezing have elapsed since application. When planting into treated areas, the risk of crop injury is less if lower rates of product were applied and conditions following application have included warm, moist soil conditions that favor rapid degradation of 2,4-D. Risk is greater if higher rates of product were applied and soil temperatures have been cold and/or soils have been excessively wet or dry in the days following application. Consult your local Agricultural Extension Service for information about susceptible crops and typical soil conditions in your area.

Restricted Entry Interval

48 hours