Twenty herbicide treatments were evaluated on conventional-till (plow, disc, and harrow), minimum-till (disc only), and no-till planted soybeans [Glycine max(L.) Merr.] from 1976 through 1978 at the Belleville Research Center in St. Clair County, Illinois. The soil type was a Weir silt loam (Typic Ochraqualf) characterized by poor internal drainage and 1.2% organic matter. Weed population by species, weed control, and soybean population, injury, and yield were obtained. Fall panicum (Panicum dichotomiflorumMichx.) and giant foxtail (Setaria faberiHerrm.) were the dominant species in all tillage systems, exceeding 1 million plants/ha in the conventional and no-till plots. These species and ivyleaf morningglory [Ipomoea hederacea(L.) Jacq.] were the most difficult to control each year. Weed control was the poorest in the no-till plots because of the large size of the weeds at the time of herbicide application, insufficient rainfall following, and because the plots were not cultivated. The soybean population was equal in all tillage systems except in 1976 when the no-till population exceeded that in the other tillage systems. Treatments that included oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) caused 42 and 35% soybean injury in the 1976 minimum and no-till plots, respectively. Postemergence-applied naptalam (N-1-naphthylphthalamic acid) plus dinoseb (2-sec-butyl-4,6-dinitrophenol) caused leaf burn each year that ranged from 5 to 35% but all plants recovered within several weeks of application. The seedbed tillage method and herbicide treatments did not significantly affect soybean yields in 1976 when all the herbicides were effective. No-till yields in 1977 and 1978 were substantially lower than yields in conventional and minimum-till plots because of poor weed control. Soybean yields were 2506, 2466, and 1714 kg/ha in the conventional-till, minimum-till, and no-till plots, respectively, when averaged over the 3 yr and 20 herbicide treatments.

Field experiments were conducted from 1993 to 1995 to evaluate control of annual weeds with glyphosate applied at rates of 560 to 2800 g ai/ha in spray volumes of 93 and 187 L/ha. Glyphosate controlled 100% of giant foxtail, fall panicum, redroot pigweed, and velvetleaf (in 1993) regardless of rate, spray volume, or application timing. Ivyleaf morningglory, velvetleaf, and common lambsquarters control was greater with glyphosate applied early POST than late POST. Ivyleaf morningglory, velvetleaf, and common lambsquarters control increased as glyphosate rate increased with both spray volumes. Velvetleaf control with glyphosate applied late POST was greater with glyphosate in 187 L/ha water compared with 93 L/ha water.

Several field studies were conducted during 1981 and 1982 to determine whether early preplant (EPP) applications of residual herbicides would prevent the establishment of vegetation before planting no-till soybeans [Glycine max(L.) Merr. ‘Williams’]. Early preplant applications of either cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} or cyanazine plus oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were applied in the fall and 3, 2, and 1 month(s) before planting no-till soybeans. In all studies, the treatments prevented vegetation from becoming established before planting, and season-long weed control was achieved with several different treatments. Early preplant cyanazine plus oryzalin provided greater than 90% control for the entire season where grass densities were low. Where grass densities were high (greater than 90% ground cover), EPP cyanazine plus a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or a postemergence application of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} controlled 90% of the weeds, which was equal to or better than the standard preemergence treatments used (80 to 98% weed control).

Field experiments were conducted over 3 yr at three locations in Illinois to evaluate the efficacy of glyphosate in glyphosate-resistant soybean planted in rows spaced 19, 38, and 76 cm. Minimal soybean injury (less than 10%) was observed from any glyphosate treatment. Glyphosate treatments controlled 82 to 99% of giant foxtail. Common waterhemp control was increased as soybean row spacing was decreased. Applying sequential glyphosate applications or increasing the glyphosate rate from 420 g ae/ha to 840 g/ha frequently increased common waterhemp control in 76-cm rows. Velvetleaf control with glyphosate was variable, ranging from 48 to 99%. Decreasing soybean row spacing, utilizing sequential glyphosate applications, or increasing the glyphosate rate improved velvetleaf control in at least four of eight site-years. Glyphosate treatments generally resulted in weed control and soybean yield equal to or greater than the standard herbicide treatments. However, glyphosate treatments yielded less than the hand-weeded control in four of eight site-years, suggesting that weed control from glyphosate treatments was sometimes inadequate.

Field studies were conducted at Carbondale and Belleville, IL to evaluate weed control in corn with a total POST herbicide program. Nicosulfuron was applied at 24 and 35 g/ha alone and in combination with 2,4-D, dicamba, bromoxynil, bentazon, atrazine, and bentazon, bromoxynil, and dicamba plus atrazine. Nicosulfuron controlled 98 to 100% of giant foxtail both years at both locations. Control of giant foxtail was reduced when nicosulfuron at 24 g/ha was applied as a tank-mix with atrazine, and with bentazon, bromoxynil, or dicamba plus atrazine at Belleville in 1991. Also, bentazon plus atrazine with nicosulfuron at 35 g/ha reduced control of giant foxtail. Control of common lambsquarters, jimsonweed, and velvetleaf was dependent on nicosulfuron rate, companion herbicide, and growing conditions. Nicosulfuron alone or as a tank-mix with the companion herbicides controlled redroot pigweed 100% at both sites both years but control of yellow nutsedge was less than 50%. Corn yield was related to level of weed control obtained in most instances.