Tordon and other herbicides. Field testing for the control of deep-rooted perennial weeds in Colorado
Down Earth 20(3): 9-12
The most serious perennial weeds in Colorado are: Canada thistle (Crisium arvense) field bindweed (Convolvulus arvensis), leafy spurge (Euphorbia esula), Russian knapweed (Centaurea repens), white-top (Cardaria draba), and two povertyweeds (Franseria sp.). 2,4-D and 2,4,5-D have not been successful in their control. Results with these and a number of other herbicides have been variable, according to conditions. Of all the materials tested Tordon (4-amino-3,5,6-trichloropicolinic acid), applied at the rate of 2 lb/acre in either spring or fall, has given commercially satisfactory control for 1 year and there has been some hold-over effect the 2nd year. At 1/2-1 1/2 lb/acre in 30 gallons of water it has also given effective control of tall larkspur (Delphinium sp.) and oak brush (Quercus gambellii).