Itchgrass (Rottboellia exaltata) Response to Control Practices in Soybean (Glycine max)

Abstract

Field studies were conducted to document the response of itchgrass [Rottboellia exaltata(L.) L.f. ♯3ROOEX] in soybean [Glycine max(L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.

Influence of Adjuvants on Itchgrass (Rottboellia cochinchinensis) Control in Corn (Zea mays) with Nicosulfuron and Primisulfuron1

“…Soil-applied herbicides metolachlor [2-chloro-N-(2-ethyl-6methylphenyl)-N-(2-methyoxy-1-methylethyl)acetamide], EPTC (S-ethyl dipropyl carbamothioate), and atrazine [6-chloro-N-ethyl-N Ј -(1-methylethyl)-1,3,5-triazine-2,4diamine] do not control itchgrass (Bridgemohan and Brathwaite 1989;Sharma and Zelaya 1986). Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] are effective soil-applied herbicides for itchgrass control in soybean (Griffin 1991;Harger et al 1982;Nester et al 1984) and sugarcane (Griffin and Lencse 1992). Pendimethalin has also been effective for controlling itchgrass in corn (Bridgemohan and Brathwaite 1989;Fisher et al 1985;Sharma and Zelaya 1986), although seed production can still occur in later-emerging plants (Bridgemohan and Brathwaite 1989).…”

Itchgrass (Rottboellia cochinchinensis) Control Options in Soybean (Glycine max)

“…With a weed such as itchgrass, which is capable of germinating season-long (2, 9) and able to persist under a shade environment (8), a season-long weed control approach would be advantageous (6). This is especially important because in this research soil-applied herbi cide treatments alone generally did not provide suffi cient season-long control.…”

“…In both years, POST herbicides were applied in 187 L ha" 1 of water at a pressure of 179 kPa. Crop oil concentrate 5 at 2.3 L ha" 1 was added to fluazifop-P, sethoxydim, halox yfop, quizalofop, and clethodim treatments, whereas 0.25% (v/v) nonionic surfactant 6 was added to the imazaquin, imazethapyr, and diclofop treatments. Vis ual itchgrass control ratings compared with an untreated check were made early-and late-season 28 and 108 DAT in 1985 and 15 and 99 DAT in 1986.…”

“…Harger et al (3) found that even though herbicides controlled itchgrass early, substantial seed production still occurred. A combination of PPI and POST herbi cides and cultivation reduced itchgrass density and standing biomass at soybean harvest (6). Itchgrass plants competing season-long in plots treated with trifluralin reduced soybean yield approximately 21 g ha" 1 per weed.…”

“…Due to the aggressiveness of itchgrass, an intense weed management program often requiring season-long weed control efforts using both PRE and POST herbi cides is essential for maximum yields (6). Information on herbicide efficacy with recently labeled PRE and POST treatments is limited.…”