In a “closed system” nutrient solution experiment, shoot growth of downy brome (Bromus tectorum L.) was: (1) more rapid during early growth, (2) accelerated earlier by nitrogen, and (3) increased more by low to intermediate levels of nitrogen than that of crested wheatgrass (Agropyron desertorum Fisch. ex Link). Shoot growth of crested wheatgrass was increased more by high levels of nitrogen and at a more mature stage of growth than that of downy brome. Root growth of crested wheatgrass was greater at all nitrogen levels than that of downy brome and was increased by the high nitrogen levels. Downy brome removed more nitrogen from solution at the intermediate nitrogen level than did crested wheatgrass and more phosphorus at both the low and intermediate nitrogen levels. At the highest nitrogen level, crested wheatgrass removed more nitrogen from solution than did downy brome.

Wild oat (Avena fatua L.) seedlings from mature seeds emerged in silt loam from depths up to 17.5 cm in the greenhouse or 15 cm under field conditions. No emergence occurred from greater depths. Under field conditions, the greatest percentage of shoots emerged from seeds planted 5 cm deep. Wild oat in a space-planted nursery produced an average of 19 tillers, reached a maximum height of 79 cm, and produced an average of 1072 seeds. The number of tillers per plant, the number of seeds per panicle, and the total number of seeds per plant increased with an increase in annual precipitation. Wild oat seeds harvested as early as 3 days after anther extrusion germinated, but seeds harvested 6 or 7 days after anther extrusion germinated more rapidly.

Honey mesquite (Prosopis glandulosa Torr. # PRCJG) was treated with four herbicides at 1.1 kg ae/ha at 14 dates from April 30 through September 23 over a 2-yr period. Overall, clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide, killing 80% or more of the honey mesquite at most dates. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were less effective than clopyralid. Honey mesquite control was correlated with Julian day of year sprayed, 15 plant, 11 environmental, and 8 herbicide concentration variables. Most effective control was negatively correlated with Julian day of year sprayed and new xylem ring thickness. Control was positively correlated with total daily apparent photosynthesis, upward methylene blue dye movement in the xylem, and herbicide concentration in the xylem 3 days after spraying. The only environmental variable of 11 measured that was significantly correlated with honey mesquite control was soil water and that was only with picloram. The concentration of herbicide in the stem was highest for clopyralid, followed by picloram, and then by 2,4,5-T and triclopyr, which were about equal. Variables most useful in regression equations for predicting control with herbicides were total daily apparent photosynthesis and rate of upward movement of methylene blue dye. Variables most incorporated into regression equations relating honey mesquite control with herbicide content were herbicide concentrations in the xylem 3 or 30 days after treatment.

Studies were conducted to characterize qualitatively and quantitatively the water-soluble carbohydrates in johnsongrass [Sorghum halepense (L.) Pers.]. Glucose, fructose, and sucrose were the only sugars detected in other than trace amounts in leaves, culms, or rhizomes. Sucrose was the major storage carbohydrate, although glucose and fructose were present throughout most of the life cycle in both leaves and rhizomes. Levels of glucose, fructose, and sucrose in rhizomes were maximum when plants began flowering and minimum at 10 to 30 days after plant emergence. Glucose, fructose, and sucrose were at a maximum in leaves within 30 days after plant emergence. Glucose was present only in trace amounts in leaves for about 10 days during initial flowering; fructose was at a maximum at that time. Sucrose in leaves occurred in greatest quantities soon after plant emergence, immediately before flowering, and after flowering. Leaf blades and sheaths contained nearly equal concentrations of carbohydrates, but stems contained greater concentrations than leaves. Basal shoots and secondary culms from nodes on primary culms contained greater concentrations of carbohydrates than leaves on primary culms. Regrowth from clipped shoots had significantly higher concentrations of glucose and sucrose than did unclipped shoots. Rhizomes of clipped plants had significantly less sucrose but more glucose than rhizomes of unclipped plants.

The amount of C14-labeled triazine herbicides absorbed by the upper and lower surfaces of peanut (Arachis hypogea) leaves was found to be significant with the exception of 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone). Almost always a surface active agent increased the absorption of triazine herbicides by the leaves. The surface active agent did not play any role in diffusion of these herbicides. Among the four herbicides tested 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone) were found to move both acropetally and basipetally, whereas 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) moved only in the acropetal direction.

A high degree of control of annual weeds in cotton by the pre-emergence application of dinitro-secondary-butyl-phenol or its salts has led to appreciable commercial interest. Leonard, et al. showed that the above chemical was promising for controlling annual weeds in cotton, when applied to the soil as a pre-emergence herbicide, and there have been many reports on the method since that time. It was recognized that this treatment did not control perennial weeds such as nutgrass and Johnson grass, and that some additional treatment would be required to control these weeds. In January 1948, one of the authors had the opportunity to see sugarcane weeds in Puerto Rico controlled by the post-emergence application of fortified oil emulsions, and the procedure was included for study in the 1948 cotton tests. The primary interest of the authors was to find a spray that would control the perennial weeds and which, at the same time, would not be injurious to cotton. It was felt that the annual weeds could be controlled rather well by the pre-emergence treatment. The effect of fortified oils and oil emulsions and unfortified oils on cotton hypocotyls and on grass shoots showed that the fortifying chemicals (dinitro-secondary-butyl-phenol and pentachlorophenol) were quite injurious to cotton hypocotyls, but that some unfortified oils showed considerable promise for selectively weeding cotton.

In one study, twelve treatments consisting of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis-(ethylamino)-6-isoproplyamino-s-triazine (simazine), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) applied alternately in a program pre- and postemergence to the weeds were evaluated on ten sugar cane plantations. Averaged data indicated that combinations including atrazine outperformed simazine in every instance and diuron was better than monuron on all plantations but one. Diuron was most effective on grasses, e.g., Digitaria spp. whereas atrazine was outstanding against Commelina diffusa Burm. In a second study on the same plantations, the initial treatment of 5 lb/A of atrazine followed by 3 lb/A of diuron gave outstanding weed control on five plantations. Using 3 lb/A of each material applied simultaneously had merit at times but some plantations required only a single application of either material. Net days of weed control obtained by diuron were inversely dependent on the amount of chemical adsorbed by the soil in both studies and total days control appeared to be dependent on ample rainfall in the second.

Glanded and non-glanded isogenic lines of cotton [Gossypium hirsutum L., var. Empire 61(WR)] were treated with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to determine the significance of lysigeneous glands in the tolerance of atrazine by cotton. The presence of lysigeneous glands did not increase atrazine tolerance by cotton or decrease the inhibition of photosynthesis by the herbicide. Detoxication of atrazine by N-dealkylation occurred in both glanded and non-glanded cotton. No significant difference in atrazine metabolism was observed between the two lines. Atrazine metabolism may be a more important factor than the presence of lysigeneous glands in the intermediate tolerance of cotton to atrazine.

Herbicide-resistant Echinochloa species are among the most problematic weeds in agricultural crops globally. Recurring herbicide selection pressure in the absence of diverse management practices has resulted in greater than 20% of sampled Echinochloa populations from rice (Oryza sativa L.) fields demonstrating multiple resistance to herbicides in Arkansas, USA. We assessed the resistance profile and potential mechanisms of resistance in a multiple herbicide–resistant junglerice [Echinochloa colona (L.) Link] (ECO-R) population. Whole-plant and laboratory bioassays were conducted to identify the potential mechanisms of non–target site resistance in this population. ECO-R was highly resistant to propanil (>37,800 g ha−1) and quinclorac (>17,920 g ha−1) and had elevated tolerance to cyhalofop (R/S = 1.9) and glufosinate (R/S = 1.2) compared to the susceptible standard. The addition of glufosinate (590 g ha−1) to cyhalofop (314 g ha−1), propanil (4,500 g ha−1), or quinclorac (560 g ha−1) controlled ECO-R 100%. However, cyhalofop applied with propanil (48% control) or quinclorac (15% control) was antagonistic. The application of the known metabolic enzyme inhibitors malathion, carbaryl, and piperonyl butoxide increased control of ECO-R with propanil (>75%) but not with other herbicides. Neither absorption nor translocation of [14C]cyhalofop or propanil was different between ECO-R and ECO-S. [14C]Quinclorac absorption was also similar between ECO-R and ECO-S; however, translocation of quinclorac into tissues above the treated leaf of ECO-R was >20% higher than that in ECO-S. The abundance of metabolites was higher (∼10%) in the treated leaves of ECO-R than in ECO-S beginning 48 h after treatment. The activity of β-cyanoalanine synthase, which detoxifies hydrogen cyanide, was not different between ECO-R and ECO-S following quinclorac treatment. Resistance to propanil was due to herbicide detoxification by metabolic enzymes. Resistance to quinclorac was due to a detoxification mechanism yet to be understood. The reduction in sensitivity to cyhalofop and glufosinate might be a secondary effect of the mechanisms conferring high resistance to propanil and quinclorac.

Galston and Baker have established that riboflavin is a photoreceptor in the destruction of auxin by visible light by in vivo and in vitro experiments. Carrol showed that riboflavin also reduced the activity of 2,4–dichlorophenoxyacetic acid (2,4–D). He believed that the reduction in activity occurred only in the presence of living plant material. The present studies using corn seedlings confirm the reduction in 2,4–D toxicity by riboflavin when the seedlings and substrate were illuminated. In addition, the inactivation of 2,4–D by riboflavin by light in vitro was also shown.

Winter wheat (Triticum aestivum L., var. Gaines) plots infested with seedling blue mustard (Chorispora tenella (Willd.) DC) were hand-weeded or treated in the fall with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) at 1 lb/A and 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) at ⅜ lb/A. Additional wheat plots were established in the fall with populations of one, three, and nine blue mustard seedlings per square foot, and the next spring these were either untreated, hand-weeded, or treated with (2,4-dichlorophenoxy)acetic acid (2,4-D) at 1 lb/A. All plots were harvested in July. Maximum wheat yields were obtained from plots hand-weeded or treated in the fall. Wheat production decreased significantly as weed population increased. Grain yield reduction, resulting from weed competition during the winter months, was significant and accounted for more than 50% of the total loss.

Experiments were conducted at Crawford and Kimball, Nebraska, during 1962, 1963, 1964, and 1965 to determine the effect of 13 herbicides on plains pricklypear (Opuntia polyacantha Haw.). The best control was obtained with 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), 4-amino-3,5,6-trichloropicolinic acid (picloram), 3,6-dichloro-o-anisic acid (dicamba), and (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T). Silvex and picloram were superior to dicamba and 2,4,5-T in controlling plains pricklypear, but picloram and dicamba injured the native grasses. Rotary hoeing plains pricklypear cladodes just prior to spraying improved herbicide performance. Simulated railing was not a consistent control measure. Evaluation of plains pricklypear control was made 1 and 2 years after herbicide application.

Fluorescence spectroscopy offers several advantages over other methods of detection and quantitation of chemical compounds. This technique has been underutilized in detection and quantitation of herbicides. The fluorescence properties of 39 herbicides representing several major types of chemistry were determined. The fluorescence of analytical standards was measured in acetonitrile, acetonitrile + water, and acetonitrile + water + strong acid. Fourteen of the 39 herbicides fluoresced to some extent, and seven (bentazon, chloramben, difenzoquat, fluometuron, imazaquin, MCPA, and norflurazon) were identified as good candidates for further method development. The technical advantages and disadvantages of fluorescence spectroscopy of herbicides are discussed.

Absorption, translocation, root release, and metabolism of imazethapyr by leafy spurge were determined under growth chamber conditions. 14C-imazethapyr was applied to vegetatively propagated leafy spurge plants in a 1% solution of 28% urea ammonium nitrate containing 0.25% by vol nonionic surfactant Plants were harvested 2 and 8 d after herbicide application. Imazethapyr absorption increased from 9% at 2d to 20% at 8d. Acropetal and basipetal translocation out of the treated leaf was observed, with 3.4 to 4.2% of the applied radioactivity accumulating in the root by the end of the 8-d time course. Eight days after herbicide application, radioactivity in dormant and elongated adventitious shoot buds was twofold higher than in root tissue (compared on a dry wt basis). Two days after herbicide application, 93% of the radioactivity remained as intact imazethapyr in the treated leaf, crown, root, and shoot buds. Eight days after application, crown, roots, and adventitious shoot buds had metabolized an average of 61, 36, and 47% of the imazethapyr, respectively, while only 14% was metabolized in the treated leaf. The primary metabolite cochromatographed with 5-hydroxyethyl-imazethapyr standard.

Control of the annual weed, common groundsel, may be troublesome because of insufficient control by herbicides. Biological control based on stimulating epidemics of the rust fungus Puccinia lagenophorae on common groundsel populations may be an alternative to herbicides if the rust fungus can be integrated with the general use of herbicides against other weeds. Formulations of monolinuron, metoxuron, and pendimethalin were selected for the study. The integration of the rust fungus with each of the three herbicides was evaluated. A three-step procedure was followed to evaluate the integration of the rust fungus and these formulated herbicides. The effect of the selected herbicides on common groundsel was tested in the first step. Only formulated monolinuron completely controlled common groundsel under controlled conditions, indicating that biological control is not required in situations where monolinuron is employed for weed control. The effect of metoxuron and pendimethalin on the rust fungus was tested under controlled conditions in the second step. Formulated metoxuron was not compatible with the rust fungus, indicating that biological control cannot be employed in situations where metoxuron is applied. The effect of pendimethalin on P. lagenophorae epidemics was evaluated using an epidemiological model in the third step. Formulated pendimethalin had no detectable effects on P. lagenophorae epidemics. We concluded that use of P. lagenophorae epidemics for common groundsel control is complementary to application of formulated pendimethalin against other weeds.

Field studies were conducted from 1988 through 1990 in Fayetteville, AR, to measure competitiveness of spotted spurge in cotton. Population levels were established by transplanting seedlings from other field areas. There was a positive linear relationship between cotton boll numbers and seed cotton yield. Percent reduction in cotton height, leaf area, dry weight, boll numbers, and seed cotton yield increased as spotted spurge densities increased. Seed cotton yield reduction was 47, 57, and 85% for spotted spurge densities of 5, 10, and 50 spotted spurge plants m–1 of row.

A biotype of johnsongrass cross resistant to clethodim, sethoxydim, quizalofop-P, and fluazifop-P was identified in several fields in Washington County, MS. Absorption, translocation, and metabolism studies using 14C-clethodim and acetyl-coenzyme A carboxylase (ACCase) activity assays were conducted to determine the resistance mechanism. Absorption of 14C-clethodim was higher in the resistant than the susceptible biotype 4 hours after treatment (HAT), but at 24, 48, and 72 HAT, similar levels of radioactivity were detected in both johnsongrass biotypes. Consequently, resistant plants had more radioactivity present in the treated leaves at 4 and 24 HAT. However, there was no difference between resistant and susceptible biotypes in the translocation of 14C out of the treated leaf at 4, 8, 24, 48, and 72 HAT as a percentage of total absorbed. Metabolism of clethodim was similar in the resistant and susceptible biotypes. There was no difference in the specific activity of ACCase from the susceptible and resistant johnsongrass biotypes (means of 0.221 and 0.223 nmol mg−1 protein min−1, respectively). ACCase from the susceptible biotype was sensitive to clethodim, with an I 50 value of 0.29 μM clethodim. The ACCase enzyme from the resistant biotype was less sensitive, with an I 50 value of 1.32 μM clethodim. The resultant R/S ratio for clethodim was 4.5. These results indicate that resistance to clethodim in this johnsongrass biotype resulted from an altered ACCase enzyme that confers resistance to clethodim.

Five herbicides were applied postemergence to three Louisiana sugarcane (Saccharum officinarum L.) varieties. Nine or 12 lb/A of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) severely injured varieties C.P. 44-101 and C.P. 52-68, but variety N.Co. 310 was not affected. Conversely, N.Co. 310 was injured more by 2,2-dichloropropionic acid (dalapon) than the other varieties. Trichloroacetic acid (TCA) + 2,4-dichlorophenoxyacetic acid (2,4-D) at 10.6 plus 3 lb/A, reduced the yield of variety N.Co. 310 in one of 2 years only. This treatment had no adverse effect on yields of the other two varieties. All varieties appeared tolerant to 2,3,-6-trichlorophenylacetic acid (fenac) applied at 4 to 12 lb/A. Diuron injured a sensitive variety both when the foliage was sprayed and when only the ground at the base of the cane was sprayed. Plants treated in May were injured more than those treated 30 days earlier.

Research on the timing of herbicide application on no-till sorghum [Sorghum bicolor (L.) Moench.] planted into undisturbed winter wheat (Triticum aestivum L.) stubble was conducted at North Platte, NE, during 1980–1982. Applying some herbicides 41 and 25 days prior to planting sorghum maintained weed control, reduced sorghum injury, and increased sorghum yields when compared to application at planting. It was necessary to apply cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} at 2.7 kg ai/ha 41 days prior to planting to avoid sorghum injury. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] + 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 + 0.3 kg/ha reduced grass yields 97, 98, and 99%, while reduction with alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] + 2,4-D at 2.8 + 0.3 kg/ha was 93, 41, and 63%, respectively, when herbicides were applied 0, 25, and 41 days prior to planting.

Protoplasts were isolated from quackgrass to investigate the influence of two surfactants and ammonium sulfate on glyphosate uptake. Without adjuvants, the uptake of glyphosate was not detectable. The uptake of the reference compound 2-aminoisobutyric acid was linear with time and was inhibited 60% in the presence of 10 μM carbonyl cyanide m-chlorophenylhydrazone. Glyphosate uptake increased in the presence of both surfactants and ammonium sulfate. After 0.5 h of incubation the internal glyphosate concentration was 37% of the external concentration (100 μM) in the presence of 0.025 g L−1 Ethomeen T/25, 21% in the presence of 0.25 g L−1 Atplus 201, 13% with 5 mM ammonium sulfate, and 20% with 50 mM ammonium sulfate. The surfactant treatments did not reduce either the viability or the internal pH (= 7.1) as judged by fluorescein diacetate staining or 5,5-dimethyloxazolidine-2,4-dione distribution, respectively. The treatments with ammonium sulfate slightly increased the internal pH. The concentration of Ethomeen T/25 required to disrupt the protoplasts was 0.075 g L−1; Atplus 201 did not disrupt the protoplasts at concentrations up to 10 g L−1.