Retention, absorption, translocation, and metabolism of 2,4-D [(2,4-dichlorophenoxy)acetic acid] by common waterplantain (Alisma triviale Pursh. # ALSPA) at three growth stages were investigated to determine the basis for differential susceptibility of common waterplantain at different growth stages. Plants in the five-leaf and scape elongation stages retained more 2,4-D than plants in the early flowering stage. Absorption of 14C-2,4-D by the flower stalk was less than absorption by the treated leaves regardless of growth stage. The majority of the absorbed 14C translocated out of the treated plant part was recovered in the aerial portion of the plant younger than the treated leaves or in the corm, with greater movement of 14C into the corm at the older growth stages. Metabolism of 14C-2,4-D did not differ among the growth stages. The results suggest that the greater sensitivity of common waterplantain at the scape elongation stage to 2,4-D is due to greater translocation to the corm when compared to the five-leaf stage, and greater retention when compared to the early flowering stage.

Field experiments were conducted to evaluate the effect of application time on common waterplantain control in wild rice with MCPA and 2,4-D. Common waterplantain control was greatest when MCPA or 2,4-D were applied at 1.1 or 1.7 kg ai/ha at the two-aerial leaf stage. The best late-season control was MCPA applied at the scape elongation growth stage. Common waterplantain was controlled adequately when 0.6 to 0.8 kg/ha of MCPA were applied at the scape elongation or early flowering stage. However, because of common water plantain interference and sensitivity of wild rice to late herbicide applications, the best treatment stage for wild rice yield was when MCPA was applied at 0.6 kg/ha to common waterplantain at the two-aerial leaf stage. Wild rice at this time is at the more tolerant one-aerial leaf growth stage.