Primary Root Elongation of Three Weed Species

Primary root elongation of prickly sida ( Sida spinosa L.) at pH 5.5 was similar to that at pH 6.5 while sicklepod ( Cassia obtusifolia L.) was reduced to 62% and tall morningglory [ Ipomoea purpurea (L.) Roth] to 87% of that at pH 6.5. At pH 5.1, root elongation of prickly sida was reduced to 77% of that at pH 5.5. Some elongation was observed in the pH range of 5.1 to 6.5 for all species. Maximum primary root growth of tall morningglory, sicklepod, and prickly sida occurred at approximately 32° which was similar to that for cotton ( Gossypium hirsutum L. ‘Empire’). Temperature as high as 39° did not significantly reduce root elongation of sicklepod. Tall morningglory root growth was reduced approximately 50% by 0.2 ppm of trifluralin (α,α,α-trifluro-2,6-dinitro- N,N -dipropyl- p -toluidine). In contrast, sicklepod and prickly sida root growth was reduced only slightly by 1 ppm of trifluralin.