Competition studies in field trials were conducted between common purslane (Portulaca oleracea L.) and table beets (Beta vulgaris L., var. Detroit Red) and between common purslane and snap beans (Phaseolus vulgaris L., var. Eastern Butter). Common purslane control was most critical during the first 2 weeks after beet and bean emergence. Common purslane control for longer than 2 weeks did not increase beet or bean yields. The longer common purslane was allowed to compete after beet or bean emergence, the more yields were decreased. Common purslane was a stronger competitor in beets than in beans. The faster and taller-growing bean plants provided more competition than did beets. Cultivation between rows until lay-by increased both beet and bean yields.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) killed nearly 100% of the wild garlic (Allium vineale L.) plants when applied in spring, but was less effective when applied in the fall. Treatment in the spring with paraquat consistently killed more wild garlic plants than treatments at any other date. Eradication of a wild garlic infestation was achieved after applications for three successive springs. Near eradication was achieved with two annual applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Among herbicides evaluated postemergence on wild garlic, mefluidide (N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], asulam (methyl sulfanilylcarbamate), and picloram (4-amino-3,5,6-trichloropicolinic acid) were not effective for controlling wild garlic. Glyphosate [N-(phosphonomethyl)glycine] and a mixture of cyperquat (1-methyl-4-phenylpyridinium) and 2,4-D ester reduced wild garlic populations by over 60%.

Blackgrass (Alopecurus myosuroides Huds.) and silky windgrass [Apera spica-venti (L.) P. Beauv.] are becoming a significant problem in Europe. Due to the development of herbicide-resistant biotypes and unwanted side effects of herbicides, there is a need for new integrated weed management strategies to control weeds. Therefore, reducing weed infestations by targeting seed production during crop harvest should be considered. In 2017 and 2018, we estimated the fraction of the total seed production of A. myosuroides and A. spica-venti in a field that potentially could be collected by a grain harvester during winter wheat (Triticum aestivum L.) harvest. Twenty plants of each species were surrounded by a porous net before flowering to trap shed seeds during reproductive development. Seeds were collected and counted weekly up until and immediately before wheat harvest, and the ratio of harvestable seeds to shed seeds during the growing season was determined. Alopecurus myosuroides produced on average 953 seeds plant−1 in 2017 and 3,337 seeds plant−1 in 2018. In 2017 and 2018, 29% and 37% of the total A. myosuroides seeds produced, respectively, were retained on plants at maturity. Apera spica-venti produced on average 1,192 seeds plant−1 in 2017 and 5,678 seeds plant−1 in 2018, and retained 53% and 16% of the seeds at harvest, respectively. If a grain harvester potentially collected approximately 30% of the total seed production of the two grass weeds and removed or killed them, it would reduce seed input to the soil seedbank. However, such methods cannot stand alone to reduce weed pressure.

Adsorption of l-butyl-3-(3,4-dichlorophenyl)-l-methyl-urea (neburon), determined spectrophotometrically, varied considerably among representative soils of six Hawaiian great soil groups, ranging from 29% in Lualualei soil to 94% in Honouliuli soil. The adsorption of neburon was strongly correlated with organic matter and total soil nitrogen; other soil properties were not related.

Initial and residual neburon phytotoxicity to oats in the greenhouse was dependent on total soil nitrogen, organic matter, and the degree of neburon adsorption. Based on ED50 values, neburon toxicity in soil types decreased in the following order: Lualualei, Wahiawa, Mahana, Paaloa, Waimanalo, Kapaa, and Honouliuli. Complete neburon inactivation was obtained in Honouliuli and Waimanalo soils within the 150-day duration of this experiment, and nearly complete inactivation in Mahana and Kapaa soils.

Herbicide performance was markedly altered by soil incorporation, depth of incorporation, crop seed placement, soil type, and rainfall. Of the 25 herbicides studied, 2-chloro-N,N-diallylacetamide (CDAA) and isopropyl-N-(3-chlorophenyl)carbamate (CIPC) and mixtures of them showed most promise. Herbicide-placement studies showed that the selectivity of these herbicides in cotton largely depends on herbicide placement in relation to the crop seed and on rainfall. Without rainfall, CDAA incorporated in moist soil above the cotton seed provided excellent weed control with minimal injury to cotton. CDAA was readily leached from the zone of germinating weed seed by rain or irrigation on coarse-textured soils. Without rainfall, CIPC was slightly inferior to CDAA in weed control but more stable in performance over a wider range of environmental conditions. Mixtures of CDAA and CIPC were somewhat superior to either alone. Commercial usage of these herbicides in moist soil depends on the development of suitable equipment for application.

Most of the 3-amino-2,5-dichlorobenzoic acid (amiben) absorbed by treated plants was converted to N-glucosyl amiben in the roots. Only small amounts of amiben and N-glucosyl amiben occurred in stems and leaves. The N-glucoside was not metabolized further and remained in vegetative tissue of soybeans for at least 50 days. Soybeans which were depleted of carbohydrate reserves by starvation in the dark absorbed less amiben and produced less N-glucosyl amiben than did plants treated under normal illumination. A similar trend was noted for tomato plants treated in a comparable manner.

A natural product in corn, the 2-glucoside of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, is capable of inactivating triazine herbicides. Two essentially isogenic corn lines, Mississippi selection GT112 (susceptible to atrazine and simazine) and GT112 RfRf (resistant), contained the compound in both roots and shoots. The content of the roots was about equal for the two lines and decreased with age. In shoots of GT112 seedlings 13 to 28 days old, the 2-glucoside content reduced with time to half the original value. In shoots of GT112 RfRf, the 2-glucoside content doubled from 13 to 17 days, then decreased. Shoots of GT112 RfRf contained 1.6, 3.6, and 2.4 times more 2-glucoside at 13, 17, and 28 days, respectively, than GT112. However, 13-day-old homogenized shoots of GT112 converted 1.8 times more atrazine per μM of 2-glucoside than GT112 RfRf. Susceptibility of GT112 to triazine herbicides is not due to absence of the 2-glucoside or its inability to convert atrazine.

Horsenettle (Solanum carolinense) is a drought-resistant, deep-rooted perennial plant that propagates itself from rhizomes and seed, both of which are produced in abundance. In pastures propagation from seed is probably of minor importance as compared to the steady increase in infestation occurring from rhizome growth.

Field dodder (Cuscuta campestris Yunck.) emerged as well in total darkness as in light, but seedlings did not twine about the host. Under the shade of alfalfa, dodder emerged normally, but attachment was reduced more than 90% and delayed 7 to 10 days. Attached dodder shaded by alfalfa did not develop its characteristic golden color, grew very slowly, and was delayed in maturity 3 to 4 weeks.

A weevil, (Rhinocyllus conicus Froelich) was introduced into Missouri in 1975 to aid in reducing populations of musk thistle, (Carduus nutans L.). The weevil was recovered in 1976 from as far as 3.2 km from the release site and 4.8 km in 1977. Infestation levels of flower heads at the release site ranged from 46 to 90%. Native parasites (Bracon mellitor Say) and [Aliolus curculionis (Fitch)] were reared from weevil larvae.

We sprayed yellow nutsedge (Cyperus esculentus L.) with 0.56, 1.12, and 2.24 kg/ha of (2,4-dichlorophenoxy)acetic acid (2,4-D) at the two and four-leaf stages in both field and growth chamber studies. Compared to non-treated plants, these rates significantly reduced shoot weight, rhizome weight, and rhizome number 12 days after application. There were no significant differences in these growth responses among the rates tested, when applied one, two, and three times at consecutive 12-day intervals. We pretreated two and four-leaf plants with 0.56, 1.12, and 2.24 kg/ha of 2,4-D immediately before foliar application of 14C-2,4-D. The increase in pretreatment rates decreased the percentage of the applied radioactivity which was absorbed and translocated. Of the radioactivity absorbed, a rather constant percentage translocated from the treated area in the different treatments. The radioactivity translocated from the application site for at least 288 hr after treatment. Less than 19% of the 14C-2,4-D applied was absorbed into the leaves 24 hr after application. Ninety-eight to 100% of the methanol-soluble radioactivity that translocated to developing leaves, rhizomes, and roots chromatographed identically to 14C-2,4-D.

Maximizing weed seed exposure to seed predators by delaying post-harvest tillage has been suggested as a way to increase weed seed loss to predation in arable fields. However, in some areas of northeastern Spain, fields are still tilled promptly after cereal harvest. Tillage usually places seeds in a safer environment compared to the soil surface, but it can also increase seed mortality through seed decay and fatal germination. By burying the seeds, tillage also prevents weed seed predation. Weed seed fate in a tilled vs. a no-till environment was investigated during the summer fallow months in three cereal fields in semi-arid northeastern Spain. Rigid ryegrass and catchweed bedstraw seeds were used. Predation rates were measured in a no-till area within each field in 48-h periods every 3 wk, and long-term predation rates were estimated. Fate of buried seeds was measured by burying 20 nylon bags with 30 seeds of each weed species from July to September at a depth of 6 cm in a tilled area contiguous to the no-till area. Predation rates over the entire summer were 62% and 49% for rigid ryegrass and catchweed bedstraw, respectively. High availability of crop seeds (preferred by ants) on the soil surface may have decreased predation of weed seeds early in the season. Seed loss due to burial was 54% and 33% for rigid ryegrass and catchweed bedstraw, respectively. Unusual above-average precipitation probably prompted higher than normal weed germination rates (fatal germination) in some fields, and thus led to higher seed mortality rates compared with an average year. These results suggest that leaving the fields untilled after harvest may be the optimum strategy to reduce inputs to the weed seedbank during the summer fallow period in semi-arid systems.

Phytase activity increased 2 to 3 fold in barley (Hordeum vulgare L.), 6 fold in corn (Zea mays L.), and 12 fold in squash (Cucurbita maxima Duchesne) seedlings 2 days after the initiation of germination in the dark. Most of the phytase was found in the embryo of the seed, presumably in the cotyledon(s). Gibberellic acid and benzyladenine supplied during germination exerted only limited influence on the development of phytase in these seedlings. Of the herbicides studied, only sodium arsenite exerted an influence on phytase activity per se that was of physiological significance. The presence of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-N-isopropylacetanilide (propachlor), 2,6-dichlorobenzonitrile (dichlobenil), or α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine (trifluralin) in the culture solution during germination partially inhibited the development of phytase activity. The herbicidal inhibition was enhanced if potassium phosphate at a non-inhibitory level also was present in the culture solution. The interaction of atrazine and amiben with phosphorus was not due to increased internal concentrations of inorganic phosphorus to a level inhibitory to the development of phytase activity.

Control of field bindweed (Convolvulus arvensis L.) on irrigated land was studied by application of herbicides once in the fall and then only in the spring for the next 4 yr. Control of field bindweed 8 months after a fall application of 2.2 kg/ha of dicamba (3,6-dichloro-o-anisic acid) or 3.4 kg/ha of 2,4-D [(2,4-dichlorophenoxy)acetic acid] was 90 and 83%, respectively. Spring applications of 0.28 kg/ha of dicamba, 0.56 kg of 2,4-D, or the mixture of these two herbicides suppressed the growth of field bindweed similarly each year. By the fall of the fourth year, field bindweed covered an average of 9% of the soil surface in the plots that received both fall- and spring-applied herbicide treatments, 72% in plots that received only fall-applied herbicide treatments, and 80% in the untreated plots. Yield of corn (Zea mays L. ‘Pioneer 3306’) was significantly higher in all treated plots than in the untreated check plots in 1 out of 2 yr. Yield of sorghum [Sorghum bicolor (L.) Moench ‘Pioneer 833’] was not increased significantly in any treated plots, but in 1 yr the mixture of 0.28 kg/ha of dicamba plus 0.56 kg/ha of 2,4-D reduced yield significantly when this mixture was applied twice at these same rates in the spring.

A plant response study was conducted in the greenhouse to evaluate interactions between imazamox and acifluorfen, fomesafen, or lactofen. Antagonistic interactions between imazamox and acifluorfen or fomesafen affected control of I. hederacea and A. theophrasti 21 d after treatment. Combinations of imazamox plus lactofen also antagonized control of I. hederacea. I. hederacea absorbed less 14C-imazamox when applied with nonlabeled acifluorfen, but absorption by A. theophrasti was not affected by the combination. Addition of nonlabeled lactofen did not affect absorption of imazamox in A. theophrasti or I. hederacea. Addition of acifluorfen or lactofen reduced translocation of 14C-imazamox to foliage above and below the treated leaf and the root in both A. theophrasti and I. hederacea. Antagonism of A. theophrasti control was due to reduced translocation of imazamox. Antagonism of I. hederacea control was due to reduced translocation of imazamox when applied with lactofen or reduced absorption and translocation when applied with acifluorfen.

In glasshouse experiments, Panicum repens rhizomes with more than two nodes emerged from soil depths of 1 to 20 cm. Emergence from one-node rhizomes was greatly reduced at depths more than 5 cm. In contrast, culm emergence from ginger like rhizomes decreased when burial depth (BD) was greater than 20 to 30 cm. P. repens emerged from deeper soil levels with an increasing number of nodes per cutting. Culms emerged from 36% of total underground regenerative organs. About 75 and 95% of the emerged culms were recorded 30 and 60 d after burial, respectively, and 91% emergence was recorded from 20-cm BD. In field studies, only 9% of nodes produced culms following cross-plowing. About 61 and 67% of the emerged culms were recorded 50 and 60 d after land preparation, respectively. Results indicate that mechanical and chemical control methods could be most effective for P. repens when applied approximately 50 d after land preparation. Burying deeper than 30 cm by deep plowing and reducing rhizome length by cross-plowing might effectively reduce emergence of P. repens.

The techniques of cryostat sectioning, freeze-drying, and microradioautography were adapted to study the absorption and translocation of radio-labeled 3-(3,4-dichlorophenyl)-1,1-dimethylurea (14C-diuron) in root-treated cotton (Gossypium hirsutum L., var. Coker 201) plants. Diuron appeared to move primarily in the apoplast and to be transported acropetally and laterally in the transpiration stream. Radioactivity was observed to accumulate in striking concentrations in the lysigenous, or pigment, glands and the trichomes of the cotton plant. This accumulation is postulated to be a major factor in lowering the effective concentration of the herbicide in the leaves of cotton as compared to leaves of more susceptible plants, and thus may be a significant factor in the tolerance of cotton to diuron.

Mechanical wounding broke dormancy and promoted germination of primary dormant pure-line wild oat (Avena fatua L. # AVEFA) caryopses that were in the first physiological stage of dormancy. Caryopses incubated in petri dishes responded to wounding by germinating more rapidly than wounded caryopses incubated in soil. There was no difference in germination between wounded and lanolin-covered wounded caryopses when incubated in soil. The less dormant AN265 caryopses responded to the wounding treatment more rapidly than the more dormant caryopses of M73 in both petri dish and soil incubation systems. Chlorocholine chloride (CCC), an inhibitor of gibberellic acid (GA) biosynthesis, reduced the germination rate of wounded AN265 and M73 caryopses above and at 1 mM, respectively. Application of 25 mM CCC to wounded dormant AN265 caryopses decreased the level of hexose in the embryo to 47% of the control level. There was no significant effect of CCC on the endosperm hexose, embryo and endosperm imbibed fresh weight, and sucrose and starch content. The results suggest GA or GA biosynthesis is the limiting factor to germination.

The reduction in root yield (Y) of sugarbeets (Beta vulgaris L.) caused by specific densities (X) of kochia [Kochia scoparia (L.) Schrad.] was predicted by using the linear equation Y = 4.30 + 1.81 X. This equation was most accurate when the kochia density was 20 plants or less per 30.5 m of row. In 28 of 30 weed-control systems, where kochia densities ranged from 0.2 to 16.5 plants per 30.5 m of row, the predicted yield reductions were within 5% of the actual yield reductions.

Field and laboratory studies were conducted at Stoneville, MS, from 1996 to 1998 to determine the influence of subsoiling (SS) and conventional tillage (CT) of a Sharkey clay soil on microbial characteristics and herbicide degradation. Soil samples obtained from imazaquin-treated and nontreated plots from the soybean row and interrow position were analyzed. Because only the row position is actually disturbed by SS, a comparison of row and interrow position on the parameter was conducted. Imazaquin (preemergence, 140 g ai ha−1) had no effect on microbial populations, microbial enzyme activity (fluorescein diacetate [FDA] hydrolysis and triphenyl-tetrazolium chloride [TTC] dehydrogenase), and organic carbon content. Estimates of microbial activity based on FDA hydrolysis and TTC dehydrogenase activity indicated greater activity under CT; however, microbial biomass and organic carbon were not affected by tillage or row position. A laboratory study assessed the degradation of carboxyl- and ring-labeled 2,4-D as influenced by tillage and row position. Soils from CT plots had an initially higher mineralization rate of 14C carboxyl-labeled 2,4-D compared to soils from SS plots; however, no effect of tillage or row position was observed on the cumulative amount of 14CO2 evolved 14 d after treatment (DAT) in 1996 and 18 DAT in 1998. In studies with ring-labeled 2,4-D, a higher 14CO2 evolution was detected in soils obtained from SS plots, regardless of row position, whereas a greater amount of radioactivity was observed in the unextractable fraction from CT soils. Because differences in 2,4-D mineralization between tillage regimes were minimal, adoption of SS as a tillage practice for heavy clay soils in the Mississippi Delta may have a limited effect on microbial characteristics and biodegradation of soil-applied herbicides.