Field trials were conducted in Virginia to evaluate trumpetcreeper control with glyphosate and conventional herbicide systems in double-crop glyphosate-resistant soybean. When compared with the untreated control, none of the conventional herbicide systems evaluated in these trials provided any reductions in the trumpetcreeper stem density at 1 yr after treatment (YAT). Glyphosate systems generally provided much higher levels of trumpetcreeper stem reduction than conventional herbicide systems. By 1 YAT, densities of trumpetcreeper that received conventional herbicide treatments ranged from 97 to 141% of the initial population, whereas densities of trumpetcreeper that received preemergence (PRE) followed by postemergence (POST) or POST-only applications of the isopropylamine (IPA) or diammonium (DIA) salts of glyphosate ranged from 30 to 66% of the initial population. However, PRE applications of the IPA or DIA salts of glyphosate generally provided lower levels of trumpetcreeper stem reduction than PRE followed by POST or POST-only applications. These results indicate that glyphosate applications made later in the growing season will provide greater trumpetcreeper stem reductions than those made at or close to soybean planting in double-crop soybean production systems. Glyphosate systems did not provide higher soybean yields than the untreated control that contained trumpetcreeper only when densities averaged 6 trumpetcreeper stems/m2 in 2000, but 12 of the 16 glyphosate-containing treatments provided higher soybean yields than the untreated control that contained trumpetcreeper only when densities averaged 13 stems/m2 in 2001.
Nomenclature: Glyphosate; imazamox; lactofen; paraquat; trumpetcreeper, Campsis radicans (L.) Seem. ex Bureau #3 CMIRA; soybean, Glycine max (L.) Merr. ‘Asgrow 4902 RR’, ‘Asgrow 5401 RR’.
Additional index words: Acifluorfen, cloransulam, fomesafen, formulations, herbicide application timing, no-till, perennial weed control.
Abbreviations: DIA, diammonium; IPA, isopropylamine; POST, postemergence; PRE, preemergence; YAT, years after treatment.