Five biotypes of common cocklebur that were not controlled with acetolactate synthase (ALS)-inhibiting herbicides were tested in greenhouse and laboratory studies to determine the magnitude of resistance and cross-resistance to four ALS-inhibiting herbicides. In vivo inhibition of ALS was also evaluated. Based on phytotoxicity, all five ALS-resistant biotypes of common cocklebur were > 390 times more resistant than the susceptible biotype to imazethapyr. However, only four of these biotypes were also resistant to another imidazolinone, imazaquin. Two biotypes were cross-resistant to the sulfonylurea, chlorimuron, and the triazolopyrimidine sulfonanilide, NAF-75. One biotype demonstrated intermediate susceptibility to imazaquin, chlorimuron, and NAF-75. In all cases, the resistance exhibited at the whole plant level was associated with an insensitive ALS.

Rates of 0, 1.7, and 3.4 kg/ha of 3-amino-2,5-dichlorobenzoic acid (chloramben) were incorporated to 0, 3.8, and 7.6-cm depths in 0.7 by 0.7-m microplots under low, moderate, and high rainfall conditions. Soybean [Glycine max (L.) Merr., var. Amsoy] injury increased with increasing depth of incorporation of 3.4 kg/ha chloramben. Chloramben incorporation under low rainfall conditions significantly improved control of giant foxtail (Setaria faberii Herrm.), smooth pigweed (Amaranthus hybridus L.), and velvetleaf (Abutilon theophrasti Medic.) compared to surface treatments. Jimsonweed (Datura stramonium L.) was not controlled well by chloramben regardless of rate or incorporation depth. In larger field plots over a 3-year period, 3.4 kg/ha chloramben incorporated with a disc produced slight but insignificant soybean injury. Giant foxtail, smooth pigweed, common ragweed (Ambrosia artemisiifolia L.), and velvetleaf control with incorporated chloramben was equal to or better than the control obtained with surface-applied chloramben. Regardless of method of application, control of common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed, and annual morningglory (Ipomoea spp.) was poor.

Tubers of yellow nutsedge (Cyperus esculentus L.) were buried in the field 2.5 to 30.5 cm below the surface in November 1969 and 1970 at Urbana, Illinois. In both years, shoots began to emerge the following May and continued emergence until July. Very few additional shoots emerged after July. Shoots emerged from less than 2% of the tubers buried at 2.5 cm; the maximum number of shoots emerged from tubers at the 10.2 and 20.3-cm depths. Tubers at the 2.5 and 5.1-cm depths were more susceptible to winterkill than tubers at lower levels, probably because of the differences in soil temperature at these levels during cold periods. Kinetic analysis of laboratory-determined tuber viability for periods up to 22 months revealed that the half-life was 4.4 and 5.7 months for tubers buried at 10.2 and 20.3 cm, respectively. The extrapolated minimum temperature required for initiation of tuber germination in the laboratory was 12 C. This temperature minimum could not readily be related to initial shoot emergence in the field. The temperature at which 50% of the tubers survived a cold treatment for 4 to 48 hr was −7 C.

Seeds of yellow foxtail [Setaria lutescens (Weigel) Hubb.], ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed (Datura stramonium L.), velvetleaf (Abutilon theophrasti Medic.), and giant ragweed (Ambrosia trifida L.) were buried in the soil November 20 and 21, 1966 at Urbana, Illinois for noting emergence of seedlings from April 1 through August 18, 1967. Similarly, seeds of yellow foxtail, ivyleaf morningglory, jimsonweed, velvetleaf, giant ragweed, common ragweed (Ambrosia artemisiifolia L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) were buried on October 25, 1968 for emergence observations from April 1 to August 18, 1969. Pennsylvania smartweed, giant ragweed, and common ragweed had large flushes of germination from early April through early May, with no emergence after June 1. Velvetleaf displayed similar early flushes and had additional small flushes of emergence in late May or June. Yellow foxtail seedlings also emerged in April and May in 1969 and in May and June during both years. Common cocklebur seedlings emerged abundantly in April and May but less abundantly in June. Ivyleaf morningglory and jimsonweed displayed flushes of emergence sporadically after May 1. Flushes of emergence for all species which occurred after May 1 were preceded by sufficient rainfall to bring the surface 10 cm of soil to field capacity. Cumulative heat units in the soil above 10 C were not correlated with initiation of emergence for any species. The early emergence was attributed to stimuli from general soil warming while emergence after May 1 was stimulated by favorable soil moisture from rainfall.

A system for controlling yellow nutsedge (Cyperus esculentus L.) in soybeans [Glycine max (L.) Merr.] which involved preplanting tillage, late planting, herbicides, and cultivation was evaluated in 1969 and 1970. In Illinois on a Drummer silty clay loam, S-ethyl dipropylthiocarbamate (EPTC) and S-ethyl diisobutylthiocarbamate (butylate), incorporated in the soil before planting, gave good and fair control of yellow nutsedge, respectively, but both injured soybeans initially. S-propyl dipropylthiocarbamate (vernolate), also incorporated before planting, controlled yellow nutsedge as well as EPTC did, and resulted in less injury to soybeans. Soybean yields were not reduced by any of the thiocarbamate treatments. Incorporation of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) or 2-chloro-N-isopropylacetanilide (propachlor), just before planting, controlled at least 90% of the yellow nutsedge in both years, whereas preemergence applications were only moderately successful and dependent on rainfall. In field microplots, alachlor and vernolate provided only fair control of yellow nutsedge when applied to the soil surface, but they both controlled 95% of the yellow nutsedge when incorporated 7.6 cm. In greenhouse studies on selective control of yellow nutsedge in soybeans, alachlor exhibited a wider margin of safety to soybeans than did vernolate.

Laboratory, greenhouse, and field experiments were conducted in 1972 and 1973 on the efficacy of controlling yellow nutsedge (Cyperus esculentus L.) in soybeans [Glycine max (L.) Merr.] with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide], glyphosate [N-(phosphonomethyl)glycine], and perfluidone [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide]. Young nutsedge plants (four- to six-leaf stage) were more susceptible to foliar sprays of the three herbicides than were older (six- to eight-leaf stage) plants. Foliar application of bentazon resulted in slow acropetal translocation of the herbicide, but killed the parent tubers. Good coverage of the foliage by bentazon sprays is essential, because the bentazon frequently kills only the foliage contacted by the spray. Applied as a postemergence broadcast spray, glyphosate injured soybeans severely at rates higher than 0.3 kg/ha, but did not satisfactorily control yellow nutsedge at rates less than 2.2 kg/ha. Perfluidone was active on yellow nutsedge when applied to either soil or foliage; yellow nutsedge was controlled best with preplant incorporated treatments at 4.5 kg/ha. Applications of 4.5 kg/ha perfluidone in the field significantly injured soybeans and reduced yields.

A reduction in soybean (Glycine max (L.) Merr.) yield of 25% (1968) to 30% (1969) resulted from one smooth pigweed (Amaranthus hybridus L.) per ft in 30-inch rows. A giant foxtail (Setaria faberii Herrm.) infestation of one plant per ft in 30-inch rows reduced yield 13% in 1969. Harvesting before weeds were desiccated resulted in significant threshing and separating losses as speed was increased from 1 to 2 and 3 mph. Stubble, lodging, and stalk losses were more than double in the pigweed and foxtail plots when compared to the weed-free plots after weeds were desiccated by frost.

Herbicides were mixed with Drummer silty clay loam soil in 1-inch layers in the shoot, root, shoot and root, or seed zones for giant foxtail (Setaria faberii Herrm.). After 2 weeks in the greenhouse, foxtail tops were harvested and dry weights used as the measure of herbicidal effectiveness. All of the 11 herbicides evaluated caused a reduction in dry weight when placed in the shoot zone. When placed in the root zone, only 3-amino-2,5-dichlorobenzoic acid (amiben) caused a reduction in dry weight. Most herbicides were just as effective, or more so, in the shoot zone as in the seed zone. Only amiben and N-1-naphthylphthalamic acid (NPA) were more effective in the seed zone than in the shoot zone.

Delayed planting or “stale seedbed” for weed control in close-drilled (20-cm rows) soybeans [Glycine max (L.) Merr. ‘Amsoy’] was evaluated for 3 years. The system combined final seedbed preparation 3 to 6 weeks before planting with herbicide application at planting time. The best control of six weed species and highest soybean yields were obtained by a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) application at the time of seedbed preparation followed by 3-(3,4-dichlorophenyl)-1-methylurea (linuron) application at planting and by linuron application at planting without the early trifluralin application. Applications of 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) at planting, either with or without trifluralin treatments, resulted in less weed control and lower soybean yields than comparable treatments with linuron. However, even the best treatments failed to provide the weed control necessary to prevent substantial soybean yield reduction in heavy infestations of weeds that emerge in large numbers after planting, and that resist the phytotoxic action of the herbicides.

The phytotoxicity of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) usually decreased as the stage of growth of five weed species at treatment increased. Giant foxtail (Setaria faberii Herrm.), velvetleaf (Abutilon theophrasti Medic.), and the cotyledonary stage of cocklebur (Xanthium pensylvanicum Wallr.) were most resistant to the herbicide. Ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) and jimsonweed (Datura stramonium L.) were more susceptible to chloroxuron. Soybean (Glycine max (L.) Merr.) seemed less susceptible at the cotyledonary stage than at later stages. Phytotoxicity on both weeds and soybeans was increased by increased temperature and relative humidity following chloroxuron application. The phytotoxicity of chloroxuron also was increased by simulated rainfall in greenhouse studies.

Experimental objectives were to assess metribuzin tolerance of predominately privately developed soybean cultivars and to evaluate a greenhouse screening procedure. In field results in 1982, ‘Vinton 81’, ‘Northrup King 1884’ and ‘L77-1863’ soybean cultivars were extremely sensitive to metribuzin at 0.56 kg/ha, averaging 34% injury. The other 45 cultivars showed no significant injury at the 0.56 kg/ha rate, from 9 to 46% injury at 1.4 kg/ha, and 18 to 72% injury at 2.2 kg/ha. In greenhouse hydroponic studies, these same three soybean cultivars were killed, while the other 45 cultivars were injured from 15 to 82%. A good agreement of greenhouse and field data was determined, with a correlation coefficient of r = 0.82.

The response of several hundred soybean [Glycine max (L.) Merr.] cultivars to postemergence application of four herbicides was evaluated in the field, greenhouse, and growth chamber in 1970, 1971, and 1972. Postemergence application of 3.4 kg/ha of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] did not significantly reduce yields of the seven commercially important soybean cultivars evaluated. All entries in the regional breeding trials, Uniform Test I to IV, were relatively tolerant of postemergence applications of the herbicides at rates about double those required for weed control. The observed order of phytotoxicity was 3.4 kg/ha of bentazon < 3.4 kg/ha of chloroxuron [3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea] < 0.3 kg/ha of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) = 0.4 kg/ha of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid]. Of the 338 named U.S. and Canadian cultivars in the U.S. Department of Agriculture soybean germplasm collection, all but one were tolerant to a postemergence application of 3.4 kg/ha bentazon. One U.S. cultivar, ‘Hurrelbrink,’ and ten plant introductions from Japan were highly sensitive to bentazon. These 11 cultivars were also highly sensitive to bromoxynil and 2,4-DB and somewhat sensitive to chloroxuron.

Absorption and metabolism of 14C-3-amino-2,5-dichlorobenzoic acid (amiben) by six plant species were investigated for correlation with species sensitivity. Plant sensitivity was determined from amiben concentrations required to give 50% reduction of radicle extension of germinating seedlings and shoot dry weight of 10-day-old plants (I50). The I50 values showed that soybean (Glycine max (L.) Merr., squash (Cucurbita pepo L.), and ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) were tolerant, cucumber (Cucumis sativus L.) was intermediate and giant foxtail (Setaria faberii Herrm.) and velvetleaf (Abutilon theophrasti Medic.) were susceptible. Neither the amount of amiben absorbed, the transport to shoots, the concentration of radioactivity soluble in methanol, nor the distribution of radioactivity among amiben, N-(3-carboxy-2,5-dichlorophenyl)-glucosylamine (hereinafter referred to as N-glucosyl amiben), and an unidentified amiben conjugate (amiben-X) was associated with species sensitivity in 11-day-old plants. In seedling tissues, neither the concentration of methanol-soluble nor methanol-insoluble radioactivity correlated with sensitivity. Highly significant correlations between the log percentage composition of amiben, amiben-X, and N-glucosyl amiben in the methanol-soluble fraction of seedlings and log I50 for radical elongation were obtained; the correlations were negative for amiben and amiben-X but positive for N-glucosyl amiben.

Studies of the differential responses of soybean [Glycine max (L.) Merr.] cultivars to bentazon [3-isopropyl-1H-2,1,3,-benzothiadiazin-(4)3H-one 2,2-dioxide] revealed slightly greater translocation and about a twofold greater foliar absorption in the sensitive cultivar ‘PI 229.342 (Nookishirohana),’ than in the tolerant cultivar, ‘Clark 63.’ Clark 63 metabolized bentazon faster than did PI 229.342. Bentazon was metabolized to unidentified polar metabolites I and II in Clark 63, and only to metabolite II in PI 229.342. The differential absorption and metabolism resulted in a tenfold greater concentration of bentazon in the treated leaflet of PI 229.342 than in that of Clark 63 at 8 days after foliar treatment. Leaflets contained similar amounts of 14C in petiole uptake studies, but no bentazon was detected in Clark 63 leaflets 24 hr after pulse treatment, whereas about 20% of the methanol-extractable 14C from PI 229.342 leaflets cochromatographed with bentazon. Metabolite I was labile to selected enzymes with β-glycosidic activity, whereas metabolite II was unaffected. Bentazon concentrations of 30 to 50 μM inhibited O2 evolution about 50% in isolated chloroplasts from the two cultivars. Differential bentazon metabolism appears to be the main cause of the differential responses of these soybean cultivars to bentazon.

Field experiments were conducted for 2 years at Urbana, Illinois, to evaluate the response of soybeans (Glycine max (L.) Merr., var. Harosoy 63) to soil and foliar applications of 3,6-dichloro-o-anisic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and (2,4-dichlorophenoxy)acetic acid (2,4-D). Soil incorporated applications of 2,4-D or dicamba at rates up to 8 oz/A or 4 oz/A, respectively, just before planting soybeans did not reduce soybean yields significantly. Picloram, applied under the same conditions, reduced soybean yield almost 40% at ½ oz/A. Picloram at rates from ½ to 2 oz/A caused slight to moderate leaf malformation on soybeans planted the following year but did not reduce yield. Foliar applications of 2,4-D up to 2 oz/A on soybeans had little effect on yield when applied at the prebloom stage and only slightly reduced yield when applied during flowering. Dicamba and picloram injured soybeans at the prebloom stage considerably more than did 2,4-D. Dicamba and picloram severely restricted soybean development, and reduced yield markedly when applied during flowering; ½ oz/A of dicamba or ⅛ oz/A of picloram reduced soybean yield about 50%.

Field studies were conducted over a 2-year period at Urbana, Illinois, to evaluate soybean (Glycine max (L.) Merr., var. Harosoy 63 and Wayne) and weed yields as influenced by row spacing, variety, weed control methods, and 2,3,5-triiodobenzoic acid (hereinafter referred to as TIBA). Soybean yield increased and weed yield decreased as row spacing was decreased. Compared to the yield from 40-inch rows, soybean yield increase was 10, 18, and 20% for 30, 20, and 10-inch rows, respectively. Both cultivation and applications of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) controlled annual grass weeds at all row spacings. Cultivation controlled broadleaf weeds at all row spacings. Some broadleaf weeds, unaffected by trifluralin, made sufficient growth to impair soybean yields in wide rows but not in narrow rows.

Seeds of common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed (Datura stramonium L.), ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], giant ragweed (Ambrosia trifida L.), yellow foxtail [Setaria lutescens (Weigel) Hubb.], and velvetleaf (Abutilon theophrasti Medic.) were buried in the soil at depths down to 15.2 cm in November 1966. Seeds of jimsonweed, ivyleaf morningglory, giant ragweed, yellow foxtail, velvetleaf, common ragweed (Ambrosia artemisiifolia L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) were buried 2.5 and 10.2 cm below the surface in October 1968. Seeds were exhumed for periodic laboratory analyses of dormancy changes. All species except ivyleaf morningglory and common cocklebur germinated better in light than in darkness after at least one winter of burial in the soil. Seeds decayed faster at 2.5 cm below the soil surface than at 10.2 cm, but some viable seeds of all species were recovered from both depths after 3 years. The development or maintenance of hard seeds was considered the principle mechanism for seed survival for 3 years in these species.

Competition of yellow nutsedge (Cyperus esculentus L.) with corn (Zea mays L.) was evaluated in the field at various yellow nutsedge densities over a 3-yr period. A relationship between yellow nutsedge density (shoots/m2) and percentage yield reduction revealed an 8% yield reduction for every 100 shoots/m2. Two 3-yr studies were conducted to determine the most effective combination of preplant-incorporated, postemergence, or postemergence-directed treatments for yellow nutsedge control in corn. The preplant incorporated treatments were alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], EPTC (S-ethyl dipropylthiocarbamate), or nothing; postemergence treatments were bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide], two cultivations, or nothing; and the postemergence-directed treatments were ametryn [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] or nothing. One preplant-incorporated treatment of EPTC or alachlor prevented yield reductions from yellow nutsedge competition. When no control was practiced, yields were reduced 17% in a moderate yellow nutsedge infestation (initially infested with 300 tubers/m2) and 41% in a heavy infestation (initially infested with 1200 tubers/m2). Yields were reduced 7 to 8% in the moderate infestation when no preplant-incorporated treatments were used regardless of whether postemergence or postemergence-directed treatments were also used. After 1 yr, all control measures resulted in less tuber density than no control measures, but all control treatments had essentially similar tuber densities. After the second year, several herbicide treatments were as effective as hand weeding in reducing tuber density. At least 2 yr of effective control treatments were required to reduce tubers to 20% of the original density, and 3 yr of treatment to reduce the density to 15% of the original density. No combination of treatments, including hand weeding, eliminated tubers after 3 yr.

The effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybean [Glycine max (L.) Merr. ‘Wells′] development and seed yield were investigated at Urbana, Illinois, from 1974 through 1977. Increased densities of common cocklebur reduced soybean seed yield, total dry weight, and number of pods per plant. Under full-season competition, one common cocklebur/3 m of row reduced soybean seed yield by 3 to 12%. Soybean seed yield, total dry weight, and number of pods per plant increased as the length of time from soybean emergence to common cocklebur emergence increased. Common cocklebur emerging 4 weeks after soybean emergence reduced soybean seed yield by 7%. As duration of competition with common cocklebur increased, soybean seed yield, total dry weight, and number of pods per plant decreased. The reduction in soybean seed yield was less than 10% when common cocklebur was removed 6 weeks after soybean emergence. Effects of common cocklebur competition with soybeans in Illinois were similar to those observed in the southern United States.