Witchweed [Striga asiatica (L.) Kuntze] seeds conditioned for 3 weeks in either water or 0.01% (w/v) sodium hypochlorite (NaOCl) had 83 to 95% germination after being treated with dl-strigol, kinetin, zeatin, or natural stimulants from corn (Zea mays L.) root exudates. None of these compounds, however, induced germination of seeds conditioned in 0.025 or 0.050% (w/v) NaOCl. Seeds conditioned in 0.075, 0.1, or 0.15% (w/v) NaOCl had 8, 56, and 76% germination, respectively, during the first week of conditioning and 10, 100, and 100% germination after 2 weeks of conditioning. Germination in these concentrations of NaOCl was termed “atypical”.

The conditioning and germination processes of witchweed [Striga asiatica (L.) Kuntze] seeds were regulated by synthetic dl-strigol (ST) or natural stimulants (STM) present in a corn (Zea mays L.) root-exudate solution. Seeds conditioned in water for 7 and 14 days required 10−10 and 10−12M ST, respectively, to induce maximum germination (ca. 80%). Surprisingly, conditioning seeds in ST or STM had an adverse effect on the responsiveness of the seeds to the same compounds after conditioning. Compared to seeds conditioned in water, these ST- or STM-conditioned seeds required not only higher concentrations of ST or STM to induce maximum germination, but also longer immersion time to become conditioned. ST or STM inhibits conditioning and thus the regulation of germination by ST or STM depends mainly on the stage of conditioning of seeds when they are exposed to ST or STM. ST or STM stimulates germination only after a pre-germination threshold is reached during conditioning. Exposure of seeds to ST or STM before this critical level is reached apparently inhibits conditioning.

EPTC (S-ethyl dipropylthiocarbamate) was applied to seed of alfalfa (Medicago sativa L.) that was coated with a porous material consisting principally of lime or gypsum. When the treated seed was planted in the field or greenhouse, grass was controlled selectively. When seeds, each carrying 0.1 mg EPTC, were seeded 1 cm apart in rows, the rate of EPTC would have been 2 kg/ha if this quantity of EPTC had been distributed in a band 5 cm wide. Such applications controlled grass completely in bands 5 to 6 cm wide. When seeds, each carrying 0.2 mg EPTC, were evenly distributed at seeding rates of 14 or 25 kg/ha, the broadcast rates of EPTC were 1.3 and 2.2 kg/ha. Both rates controlled grass completely. Storing EPTC-treated seed for 1 yr at 5 C did not affect germination of the seed or emergence and growth of the seedlings.

Wild garlic (Allium vineale L.) plants were buried 10, 15, and 20 cm deep in soil at 2-week intervals from September 1 until November during a 4-yr period. Plants were also buried in early spring. When buried 15 to 20 cm deep after mid-October, less than 5% of the plants produced above-ground shoots during the following 2 yr. When buried 15 to 20 cm deep on April 1, no above-ground shoots were produced during the following 2 yr, but burial on April 15 was less effective. These data suggest that deep plowing at the proper date may control wild garlic if subsequent tillage is shallow enough to avoid bringing wild garlic bulbs to the surface.

Amitrole (3-amino-s-triazole), asulam (methyl sulfanilylcarbamate), glyphosate [N-(phosphonomethyl)glycine], and fosamine [ethyl hydrogen (aminocarbonyl)phosphonate] were effective in reducing the amount of shoot regrowth from field horsetail (Equisetum arvense L.) 3 months after treatment. The order of effectiveness was amitrole > glyphosate > asulam > fosamine. The advantage of adding surfactant to the spray formulation or applying herbicides to wet foliage was rate dependent for all herbicides except fosamine. Spray retention was increased by application to wet foliage and by the inclusion of surfactant in the formulation. Spray retention increased as spray volume and plant size increased and as plant growth became prostrate. A scanning electron microscope study of the shoot surfaces showed an abundance of silica-containing structures and the presence of epicuticular wax. Certain surfaces of the scale leaves did not have these characteristics, indicating that redistribution of spray to these areas may result in greater penetration with subsequent increases in herbicide performance.

Cotton [Gossypium hirsutum (L.) ‘Hancock’] lint yield or quality was not adversely affected under weed free conditions by three consecutive annual preemergence applications of up to 1.68 kg/ha fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea] alone or in combination with 0.84 kg/ha trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) preplant incorporated on silt loam soils of the Memphis catena containing less than 1% organic matter. Similar applications of fluometuron at 3.36 kg/ha delayed maturity of cotton plants and ultimately reduced lint yields. Trifluralin treatments tended to overcome the detrimental effects of high rates of fluometuron. There was no effect on fiber development and maturation because fiber length and fineness (micronaire) were virtually identical for all treatments. The effect on maturity as determined by percent first harvest was a reflection of slower plant growth and fruiting and not of the development of the fiber itself. These results indicate no detrimental effects on cotton yield, maturity, and quality from annual applications of these herbicides at rates recommended and normally used in Tennessee.

Over a 4-yr period, glyphosate [N-(phosphonomethyl)glycine] was applied over-the-top to soybeans [Glycine max (L.) Merr.] at five rates, from 0.56 to 3.36 kg/ha, at four periods of time prior to harvest, 23 to 29 days, 15 to 21 days, 7 to 12 days, and 1 to 4 days. Soybean yields were reduced when glyphosate was applied at 2.24 and 3.36 kg/ha 23 to 29 days before harvest. Soybean seed were discolored following all five rates of glyphosate applied 23 to 29 days before harvest, following glyphosate at 1.12 to 3.36 kg/ha applied 15 to 21 days before harvest, and following glyphosate at 3.36 kg/ha applied 7 to 12 days before harvest. Germination of soybean seed was reduced at 30 C only when glyphosate was applied at 2.24 and 3.36 kg/ha 23 to 29 days before harvest, or at 3.36 kg/ha applied 15 to 21 days before harvest. At alternating temperatures (10.6 C for 72 h followed by 30 C for 72 h), all treatments applied 23 to 29 days before harvest reduced soybean seed germination; glyphosate at 1.12, 1.68, and 3.36 kg/ha applied 15 to 21 days before harvest also reduced germination. Seed from plots treated with glyphosate 23 to 29 or 15 to 21 days before harvest produced atypical soybean plants. Glyphosate at 2.24 and 3.36 kg/ha applied 23 to 29 days before harvest reduced the oil content in soybean seed, but none of the treatments consistently affected the protein content.

Interference within a mixture of equal densities of common lambsquarters (Chenopodium album L.), kochia [Kochia scoparia (L.) Schrad.], and redroot pigweed (Amaranthus retroflexus L.) in sugarbeets (Beta vulgaris L. ‘Mono Hy D2’) was determined in a 3-yr field study. Yield of sugarbeet roots and sucrose per hectare decreased as intensity of competition from equal populations of these three weeds increased. At densities of 6, 12, 18, and 24 broadleaf weeds per 30 m of row, root yields were reduced 13, 24, 33, and 39%, respectively. Sucrose yields were reduced similarly. Fewer than three weeds per 30 m of row did not significantly reduce root yield. Reduction in root yield (Y) of sugarbeets caused by specific densities (X) of the three broadleaf weeds was predicted by using the linear equation Y = 1.64 + 1.88 X. The actual reductions in yield were always less than the predicted reductions when this equation was tested against 36 weed control systems because the competitive ability of broadleaf weeds that were treated with herbicides, but not killed, was suppressed during the growing season. By harvest, broadleaf weeds present in weed-control-system plots weighed an average of 75 to 85% less than broadleaf weeds present in nontreated plots.

Combinations of herbicides applied preemergence and postemergence, with and without cultivation, were evaluated for their effectiveness for controlling weeds in soybeans [Glycine max (L.) Merr. ‘Williams’]. Annual weeds were controlled best when a sequential treatment of a mixture of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] + linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] was applied preemergence, and glyphosate [N-(phosphonomethyl)glycine] was applied postemergence, followed by one cultivation. The largest soybean yields were obtained when alachlor + linuron applied preemergence was followed by a cultivation, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] applied postemergence, bentazon applied postemergence and a cultivation, or glyphosate applied postemergence and a cultivation. Regression analysis of the soybean yield vs. weed control data for all treatments indicated that soybean yields were suppressed an average of 180 kg/ha when glyphosate was applied postemergence. A cultivation in addition to the preemergence and postemergence treatments improved both weed control and soybean yield.

Over-the-top applications of metriflufen {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} at 0.6 to 2.2 kg/ha were highly toxic to johnsongrass [Sorghum halepense (L.) Pers.], but caused little visual injury to soybeans [Glycine max (L.) Merr. ‘Hill’]. Directed applications of metriflufen at 0.8 to 3.4 kg/ha provided equal and, in a few comparisons, better control of johnsongrass than did some rates of the herbicide applied over-the-top. Application of metriflufen at 0.8 and 1.7 kg/ha in directed sprays resulted in higher soybean yields than did comparable treatments applied over-the-top; yields of directed vs. over-the-top applications of metriflufen at 3.4 kg/ha resulted in statistically equal soybean yields. The research suggested that metriflufen entered johnsongrass plants through shoots and leaves and also through roots. Johnsongrass control was excellent following applications of metriflufen at 1.7 and 2.2 kg/ha without soybean injury and with greatly increased soybean yields. Results following over-the-top applications of metriflufen at 1.1 kg/ha to ‘Hill’, ‘Tracy’, ‘Lee 68’, ‘Bragg’, and ‘Forrest’ soybeans at three different stages of morphological development did not demonstrate any appreciable differences in the response of the cultivars to the herbicide.