Prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] and dinoseb (2-sec-butyl-4,6-dinitrophenol) were applied in a non-phytotoxic undiluted oil carrier to sorghum (Sorghum bicolor L. ‘RS 610’), bean (Phaseolus vulgaris L. ‘Cascade’), and cucumber (Cucumis sativas ‘Wis. SMR-18’) simultaneously or separately, where prometryn treatment was followed by dinoseb at varying intervals of time. The simultaneous application of the two herbicides resulted in an additive response on all three plants, except that a slight antagonism was observed at one rate on both bean and cucumber. A synergistic response was observed when dinoseb treatment was delayed for at least 1 day on bean and cucumber and 2 days on sorghum. 14C-prometryn (14C) movement in bean leaves was not altered by simultaneous dinoseb application.

The long-term success of weed management programs requires that all crops in a rotation receive satisfactory weed control. Band sowing with inter-band hoeing has been proposed as an innovative weed management strategy for grain crops. In the band-sowing system, crops are sown in a broadcast pattern within a band of some chosen width (here we selected 12.7 cm); weeds between bands are controlled with inter-band hoeing, with or without so-called “blind cultivation,” for example, tine harrowing. Alteration of the crop spatial arrangement from typical single-line rows to a more evenly distributed pattern aims to enhance interspecific competition while reducing intraspecific competition. Field experiments, conducted in Maine in 2016 and 2017, compared band sowing with inter-band hoeing to the region’s standard practice of planting in 16.5-cm rows and tine harrowing in four test crops: spring wheat (Triticum aestivum L. ‘Glenn’), oat (Avena sativa L. ‘Colt’), field pea (Pisum sativum L. ‘Jetset’), and flax (Linum usitatissimum L. ‘Prairie Thunder’). Band sowing improved weed control relative to the standard practice, especially in crops with greater competitive ability (wheat and oat). Despite improved weed control, in most cases, yields were unaffected by treatment. While band sowing with hoeing provided improved weed control in multiple crops, further study is warranted to optimize seeding rate, band width, and inter-band width to improve crop yields.

Sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one}, KK 80 {ethyl-4-[4-[4-(trifluoromethyl)phenoxy] phenoxy]-2-pentenoate}, and RO-13-8895 {acetone-0-2-[D-2-[δ,δ,δ-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime} did not injure plants visibly or reduce the yield of tomatoes (Lycopersicon esculentum L.). Diclofop LC [2,4-(2,4-dichlorophenoxy)phenoxy] propanoic acid] and diclofop HC in combination with oil or surfactant reduced tomato yield because tomatoes retained more of these spray solutions. No herbicide treatments injured onions (Allium cepa L.). All compounds controlled most grass weeds. Tomato plants grown at 29/18 C were injured more by some diclofop treatments than plants grown at 18/7 C. Cell membrane permeability of tomato plants treated with diclofop alone or in combination with adjuvants increased as visual injury symptoms became more severe.

Tolerance of cicer milkvetch (Astragalus cicer L.) seedlings to 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], 2,4-D [(2,4-dichlorophenoxy)acetic acid], and phenoxy-diclofop {2-[4-(2,4-dichlorophenoxy)-phenoxy] propanoic acid} mixtures was evaluated in greenhouse and field experiments. In the greenhouse, seedlings in the cotyledonary and primary-leaf stages of growth were more susceptible to 2,4-DB alone and to combinations of 2,4-DB plus diclofop than seedlings in the second- through the fifth-leaf stages. All rates of 2,4-D with or without diclofop (1.7 kg ae/ha rate) reduced seedling growth at all stages of development. In the field, 2,4-DB with or without diclofop did not reduce seedling growth. Seedling growth was suppressed by 2,4-D alone at rates of 1.02 and 1.36 kg ae/ha throughout the growing season. All combinations of 2,4-D plus diclofop suppressed seedling growth, but the suppression was particularly apparent at rates of 0.68 kg ae/ha or higher of 2,4-D.

Studies were conducted to compare physiological characteristics of linuron-susceptible and -resistant Portulaca oleracea. The susceptible biotype had heavier seed and germinated more rapidly than the resistant biotype. Eight weeks after seeding, fresh and dry weights of susceptible P. oleracea plants were significantly greater than those of resistant plants. Susceptible P. oleracea had a significantly higher CO2 assimilation rate at 30 C, but was similar to that of resistant P. oleracea at 40 C. The susceptible biotype had a significantly higher CO2 assimilation rate at CO2 concentrations ≥ 600 ppm and at incident light levels ≥ 900 µmol m−2 s−1. The susceptible biotype had higher carboxylation and photochemical efficiencies.

A single foliar application of glyphosate [N-(phosphonomethyl)glycine] at 2.2 kg/ha controlled fragrant waterlily (Nymphaea odorata Ait.). Seeds that germinated during the year of glyphosate treatment or the following spring reestablished the fragrant waterlilies. A second application of glyphosate, once the seedlings had reached the surface of the water, resulted in long-term control.

Itchgrass [Rottboellia cochinchinensis (Lour.) W.D. Clayton] is among the most troublesome weeds in subtropical climates where sugarcane (Saccharum spp. interspecific hybrids) is cultivated. Two R. cochinchinensis biotypes commonly infest sugarcane in Louisiana. The Louisiana-1 biotype is daylength neutral, but Louisiana-2 flowered when daylength decreased to 13 h. Coupled with biotype diversity, seedling emergence has been reported to occur earlier in the growing season, as sugarcane emerged from winter dormancy. Both R. cochinchinensis biotypes were established in a common garden experiment in Louisiana during periods of sugarcane development and field preparation to simulate discontinuous emergence. Plant height and raceme production were recorded weekly for each biotype and establishment timing; aboveground biomass was harvested in autumn. Louisiana’s subtropical humid climate stimulated rapid plant growth that typically began in May and persisted through September. Without sugarcane competition, maximum R. cochinchinensis heights for Louisiana-1 and Louisiana-2 were 206 and 179 cm and growing degree days to 20-cm height in 2017 ranged from 546 to 832 and 865 to 1,160, respectively. Slower initial growth reported with Louisiana-2 would allow more time for growers to treat escaped plants with POST herbicides. Total raceme production, by autumn, was zero for Louisiana-2 established in June or later, but Louisiana-1 established in June produced up to 202 racemes. The present study demonstrated the importance of managing the Louisiana-2 biotype in March and April to limit seed production, but fields infested with Louisiana-1 were at greater risk for potential crop yield loss, because plants produced high quantities of seed when established over a wide period of time.

Soybeans [Glycine max (L.) Merr.] planted conventionally or no-tillage tolerated approximately four times the recommended preemergence rates of linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] depending on the type planter used. Least injury to high rates of linuron was with a planter that placed seed slightly below the level of the surface of the field with a slightly rounded ridge of soil over the row. A planter leaving the seed under a slight furrow resulted in intermediate crop injury and a planter which deposited seed under a furrow 5 to 10 cm deep resulted in greatest crop injury. There was no consistent trend in the tolerance to linuron of soybeans planted conventionally or planted without tillage in small grain stubble with the straw removed. Row profile and its relation to seed placement was important in the tolerance of soybeans to linuron.

Witchweed, which parasitizes corn, sorghum, sugarcane, rice, and many other members of the grass and sedge family, was found in 1960 on approximately 167,000 acres of crop land in North Carolina and South Carolina. In 1957, the first year of field studies with witchweed in the United States, there was a general opinion that herbicides would never be feasible for its control. However, Figure 1 shows that witchweed-infested land will respond to methyl bromide, although the cost is prohibitive for field applications.

In contrast to the great development of chlorophenoxyacetic acids as herbicides, the fluorophenoxyacetic acids have received very little attention in weed control work, chiefly because they were difficult to synthesize. In addition until recently, they were not widely available. Thompson et al. (5) listed 2–fluorophenoxyacetic and 2–methyl–4–fluorophenoxyacetic acids as plant growth inhibitors. Crane and Blondeau (1) reported 4–fluorophenoxyacetic acid to be as effective as 4–chlorophenoxyacetic acid for inducing parthenocarpy in figs. A 100 ppm spray gave 88% fruit set with no foliar damage. Edgerton and Hoffman (2) stated that the same compound was moderately effective in delaying leaf abscission on apple trees and produced a 2,4–D-type formative effect on treated shoots. Weintraub et al. (6) showed with a bean leaf-area repression test that some of the fluorophenoxyacetic acids have a very high formative activity comparable to that of the most active chlorophenoxyacetic acids.

Several studies have been conducted concerning the action of amitrol (3–amino–1,2,4–triazole) upon certain enzyme systems. The activity of catalase from treated potato plants and barley leaves (7), leaves of potato, barley, and sunflower, and rats (2) has been reported. In all cases, amitrol depressed the activity of catalase.

It has been noted frequently that salts of 2,4–dichlorophenoxyacetic acid, such as sodium or triethanolamine salt, are effective as herbicides in regions of moderate rainfall, while in arid regions they are sometimes relatively ineffective. Usually, and particularly under arid conditions, the aliphatic esters of 2,4–D have been more effective as herbicides than the salt forms.

In using non-fortified oils for post-emergence weed control in cotton, it has been necessary to follow certain precautions because of differential plant response at different stages of cotton growth. Several workers emphasize that certain oils can be applied safely to young cotton hypocotyls three weeks after emergence, but as soon as small bark cracks begin to appear at the base of the stem, oil usually causes injury. Palmer and Ennis found that when an oil was applied to cotton stems 14 to 80 days old, it injured the stem, and reduced final yields when cotton was 27 to 59 days old at time of application. Plants less than 27 days old and more than 59 to 80 days old were not injured by the oil.

A series of three experiments was conducted from 1951 to 1963 for the control of western snowberry (Symphoricarpos occidentalis Hook.) in southern Nebraska. Western snowberry was best controlled with 2,4-dichlorophenoxyacetic acid (2,4-D) when sprayed in early full foliage. Timeliness of herbicide application was considered the most important factor in a control program. Excellent control was obtained with 1 to 2 lb/A of the isopropyl ester of 2,4-D in all studies. The triethanol amine salt of 2,4-D was less effective. A 1:1 mixture of 2,4-D + 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 1 and 2 lb/A, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) at 1 and 2 lb/A, and 3-amino-1,2,4-triazole (amitrole) at 2 and 4 lb/A were not as effective for western snowberry control as 2,4-D. Mowing was an ineffective method of control.

As reported in the previous paper, 2,4-D (2,4-dichlorophenoxyacetic acid) caused marked changes in the RNA (ribonucleic acid) content of seedling stem tissue, particularly in the microsome fraction. The ribonucleoprotein particles of the microsome fraction participate in protein synthesis and any abnormality in their metabolism could conceivably result in biochemical and physiological disorders leading to the death of the plant.

Glyphosate is a popular herbicide used to control goosegrass [Eleusine indica (L.) Gaertn.], one of the most troublesome weeds in cotton (Gossypium hirsutum L.) fields. However, high selection pressure has led to some populations being difficult to control in cotton fields in China. In this study, levels of glyphosate resistance were quantified and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) amplification was confirmed. In addition, distribution of the EPSPS gene among the chromosomes was also investigated using fluorescence in situ hybridization (FISH) methodology. One population (AHCZ) was confirmed to be glyphosate resistant with a resistance index of 3.4 and significantly reduced shikimate accumulation compared with the susceptible population. All examined AHCZ individuals exhibited no mutations in the EPSPS gene. Expression and copy numbers of EPSPS in the AHCZ population were 5.7 and 15.4 times higher, respectively, than in the susceptible population. A positive correlation was identified between signal intensities of primary anti-EPSPS antibody and copy numbers of the EPSPS protein, as indicated by immunoblot analysis. FISH results revealed that, in mitotic metaphase chromosomes, signals were observed dispersed across two sets of homologous chromosomes in a resistant individual (copy number = 31), while in susceptible individuals, signals were only partially detected in one set of homologous chromosomes. In interphase nuclei, EPSPS signals were brightest in resistant individuals compared with susceptible individuals. In conclusion, one E. indica population from a cotton field in the Anhui Province has evolved resistance to glyphosate, and EPSPS gene amplification was confirmed as the resistance mechanism.

These herbicides for vegetables in three desert areas managed under furrow irrigation exhibited extreme variability between locations in herbicide response and crop toxicity. Some treatments provided a reasonable compromise between weed control and crop injury at any one location, none met this requirement at each location. Soil-type, soil moisture at time of herbicide application, and interaction of crops and environment probably contributed to the observed variability.