Effects of 2,4,5-T, Triclopyr, and 3,6-Dichloropicolinic Acid on Crop Seedlings

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Abstract
Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and 3,6-dichloropicolinic acid were applied to the foliage of juvenile crop plants at 0.002, 0.009, 0.03, 0.14, and 0.56 kg/ha. Corn (Zea maysL.), oat (Avena sativaL.), wheat (Triticum aestivumL.), grain sorghum [Sorghum bicolor(L.) Moench], and kleingrass (Panicum coloratumL.) were generally more tolerant to the herbicides than were peanuts (Arachis hypogaeaL.), cotton (Gossypium hirsutumL.), cucumber (Cucumis sativusL.), and soybean (Glycine max[L.] Merr.). Triclopyr was usually more phytotoxic to corn, oat, grain sorghum, and kleingrass than either 2,4,5-T or 3,6-dichloropicolinic acid at 0.14 and 0.56 kg/ha, but few differences occurred among herbicides at lower rates. Kleingrass was not affected at any rate of 3,6-dichloropicolinic acid. Wheat tolerated most rates of all three herbicides. At 0.56 kg/ha, triclopyr and 3,6-dichloropicolinic acid caused greater injury to peanuts than did 2,4,5-T; whereas, 2,4,5-T and triclopyr were more damaging to cotton and cucumber than 3,6-dichloropicolinic acid. The three herbicides at 0.14 and 0.56 kg/ha killed soybeans. Soybean injury varied from none to severe at 0.002 to 0.03 kg/ha, depending upon species investigated, but many plants showed morphological symptoms typical of the auxin-type herbicides.