The weedy spurges found in the Delta region of Mississippi, U.S.A., include spotted spurge (Euphorbia maculata L. # EPHMA), nodding spurge (Euphorbia nutans Lag. # EPHNU), prostrate spurge (Euphorbia humistrata Engelm. ex Gray # EPHHT), creeping spurge (Euphorbia serpens H.B.K. # EPHSN), and hyssop spurge (Euphorbia hyssopifolia L. # EPHHS). Nodding spurge was the most common while creeping spurge was the least common. Hyssop spurge, not previously known to be in Mississippi, was found in six of the 17 counties in the Delta of Mississippi. Hyssop spurge occurs with, and had previously been confused with, nodding spurge. Diagnostic characters, special identification features, and illustrations are provided to aid in identification of these five species of weedy spurges, which occur widely in the U.S.

Comparing fitness of herbicide-resistant and herbicide-susceptible weed biotypes is important for managing herbicide resistance. Previous research suggests there is little to no fitness penalty from amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene (a mechanism of glyphosate resistance) in Palmer amaranth (Amaranthus palmeri S. Watson) in controlled studies in the greenhouse or growth chamber. A field study was conducted in North Carolina at three locations naturally infested with A. palmeri to determine vegetative, reproductive, and germination fitness of plants with and without EPSPS amplification grown season-long with cotton (Gossypium hirsutum L.). Seed number was not correlated with EPSPS copy number. However, when plants were binned into two groups, those having an EPSPS copy number ≥2 (relative to reference genes) and those having an EPSPS copy number <2, plant fresh weight and seed number were 1.4 and 1.6 times greater, respectively, for plants with fewer than 2 EPSPS copies. Amaranthus palmeri height and seed germination, and yield of cotton, did not differ when comparing the two binned groups. These data suggest that A. palmeri plants with EPSPS amplification are relatively less fit in the absence of glyphosate, but this reduced fitness does not translate into differences in interference with cotton.

The utilization of remote sensing in agriculture has great potential to change the methods of field scouting for weeds. Previous remote sensing research has been focused on the ability to detect and differentiate between species. However, these studies have not addressed weed density variability throughout a field. Furthermore, the impact of changing phenology of crops and weeds within and between growing seasons has not been investigated. To address these research gaps, field studies were conducted in 2016 and 2017 at the Horticultural Crops Research Station near Clinton, NC. Two problematic weed species, Palmer amaranth (Amaranthus palmeri S. Watson) and large crabgrass [Digitaria sanguinalis (L.) Scop.], were planted at four densities in soybean [Glycine max (L.) Merr.]. Additionally, these weed densities were grown in the presence and absence of the crop to determine the influence of crop presence on the detection and discrimination of weed species and density. Hyperspectral data were collected over various phenological time points in each year. Differentiation between plant species and weed density was not consistent across cropping systems, phenology, or season. Weed species were distinguishable across more spectra when no soybean was present. In 2016, weed species were not distinguishable, while in 2017, differentiation occurred at 4 wk after planting (WAP) and 15 WAP when weeds were present with soybean. When soybean was not present, differentiation occurred only at 5 WAP in 2016 and at 3 WAP through 15 WAP in 2017. Differentiation between weed densities did occur in both years with and without soybean present, but weed density could be differentiated across more spectra when soybean was not present. This study demonstrates that weed and crop reflectance is dynamic throughout the season and that spectral reflectance can be affected by weed species and density.

Carolina redroot [Lachnanthes caroliniana (Lam.) Dandy] is a frequent weed of New Jersey cranberry (Vaccinium macrocarpon Aiton) bogs that competes with the crop for nutritional resources. Studies were conducted in 2018 to determine the effects of planting depth, soil moisture, lighting conditions, rhizome water content, and duration of rhizome submersion under water on L. caroliniana shoot emergence, vegetative growth, and rhizome development. Only planting depth greater than 12 cm significantly reduced shoot emergence (54%), biomass shoot and root production (27% and 65%, respectively), and rhizome formation (65%) compared with a 2-cm depth. Complete inhibition of new rhizome production was observed when the rhizome water content dropped to 30%. Soil moisture ≤30% decreased shoot biomass by ≥53% compared to 60% soil moisture, but marginally affected root biomass and had no impact on rhizome formation. Rhizome submersion for at least 120 d had minor effect on shoot emergence but reduced plant biomass by ≥28% and completely inhibited the formation of rhizomes. Finally, shading did not influence emergence but had a more dramatic effect on root and shoot biomass, which were reduced by 53% and 75%, respectively, and prevented the development of new rhizomes. This study demonstrates the plasticity of L. caroliniana to drought stress or long-lasting flooding conditions, therefore preventing consideration of cranberry bed temporary flooding or limitation of irrigation volume and frequency as viable management options. Sanding would not provide a layer of material sufficiently thick for reducing L. caroliniana shoot emergence. Reducing the quantity of light reaching the soil with black tarps or promoting rapid crop canopy closure are options that can complement the use of mesotrione for controlling L. caroliniana. Future research should address the practicality of these options, especially in bogs with low L. caroliniana pressure when early-summer weed regrowth occurs following dissipation of PRE herbicide activity.

In the years that 2,4–D has been used as a selective herbicide in agricultural areas, an increasing number of reports of its injury to crops has been published. As a result of extensive investigations, lists of susceptible and resistant crops have appeared. Some of the extremely susceptible crops include cotton, sugar beets, alfalfa, tomatoes, peas, beans, cabbage, broccoli, lettuce, grapes, and many others. In response to numerous reports of 2,4–D injury to various small grains, we now consider these plants as being relatively susceptible to 2,4–D at certain stages of development also. The morphological injuries reported may be just as severe as in the case of some of the above-mentioned plants.

Herbicidal control of tall larkspur, Delphinium occidentale Wats. was investigated in the Sawtooth National Forest near Oakley, Idaho. When larkspur was in a prebud stage, 4 and 8 lb/A of the propylene glycol butyl ether esters of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) gave good control, with significant increases in yield of native grasses. At the bud and flower stages neither herbicide gave satisfactory control at 12 lb/A. Granular silvex at 400 lb/A total product (80 lb/A ae) killed all larkspur with only slight injury to rabbitbrush, sagebrush, and native grasses. A chlorate-borate (25%–75%) mixture gave a complete larkspur kill at 1740 lb/A.

A 7-foot V-plow was modified so herbicides could be sprayed beneath the soil surface in stubble mulch fallow operations. This permits the incorporation of volatile herbicides without destroying plant residues. Weed control is achieved by action of the 7-foot sweeps during the herbicide application and later by the incorporated herbicide.

The effect of herbicide and urea-ammonium nitrate (UAN) combinations on winter wheat injury in absence of noncompetitive weeds and weed control during a winter wheat-fallow and a winter wheat-sorghum-fallow rotation were investigated. Winter wheat was planted at different dates to obtain different growth stages for spraying in the spring. Winter wheat produced greater grain yields when planted Sept. 15 or Sept. 25, 1987, 1988, and 1989 vs. Sept. 1 at North Platte, NE, while at Sidney, NE, grain yield was higher in wheat planted on Sept. 10 or Sept. 20, 1988, compared to Aug. 26. Spring-applied UAN increased grain yield on wheat planted Sept. 10 compared to no UAN in 1988–89 at Sidney, but not in 1987–88, while at North Platte, grain yields were not affected by UAN. At Sidney 2,4-D ester at 0.6 kg ae ha−1, 2,4-D amine plus dicamba at 0.3 plus 0.1 kg ae ha−1, metsulfuron at 0.007 kg ai ha−1 plus 0.25% nonionic surfactant (NIS), and metsulfuron plus 2,4-D ester at 0.007 plus 0.3 kg ha−1 plus NIS decreased grain yields compared to one handweeding. At North Platte in 1988–89, when UAN was applied with 2,4-D ester, 2,4-D amine plus dicamba, or metsulfuron plus 2,4-D plus NIS grain yields were reduced compared to the handweeded check on wheat planted Sept. 15. Occasionally, metsulfuron plus 2,4-D ester plus NIS treated wheat yielded less grain than metsulfuron plus NIS treated wheat. One or more herbicide treatments reduced wheat grain yields 4 of 15 application dates. Crop injury was related to growth stage and health of winter wheat when treatments were applied. Wheat under stress was more susceptible to herbicide damage than healthy wheat. Metsulfuron and metsulfuron plus 2,4-D controlled kochia, tumble thistle, and redroot pigweed better after wheat harvest than 2,4-D or 2,4-D plus dicamba at North Platte, but allowed summer annual grass weeds to grow. Yields of grain sorghum planted after a 10-mo fallow period were higher following winter wheat treated with three of four herbicides than the handweeded treatment.

Growth chamber studies using one soil investigated the effects of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.0, 0.4, and 0.8 ppmw on the root development and the mineral status of wheat (Triticum aestivum L. ‘Neepawa’) seedlings. The 0.8-ppmw trifluralin rate increased the number of seminal roots, reduced lateral root production, decreased root extension, caused root tips to swell (club-like appearance), and reduced root dry weights. However, 0.4-ppmw trifluralin caused only slight damage to the seedlings. Towards the end of the two-week growth period, damaged seedlings showed signs of recovery, which included an increased number of seminal roots, development of normal root extensions from clubbed root tips, and development of normal lateral root patterns. Trifluralin increased percent calcium and magnesium and decreased percent nitrogen, phosphorus, and potassium in wheat plants. The nutrient concentrations were more affected in 21-day-old plants than in 35-day-old plants, indicating the wheat seedlings were able to recover from trifluralin injury.

The absorption, translocation, and metabolism of the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} by three sunflower (Helianthus annuus L.) lines was determined at 10 and 30C. Sunflower absorbed up to 27% more 14C-diclofop while growing at 30C and 90 ± 5% relative humidity (RH) than at 10C and 40 ± 10% RH. Absorption of diclofop by susceptible (170415) and tolerant (296292 and Hybrid 894) sunflower lines was similar. Translocation of 14C out of the treated sunflower leaf was greater at 30 (1.3%) than 10C (0.5%) 192 h after treatment when averaged across sunflower lines. The diclofop-susceptible line exported more of the applied diclofop from the treated leaf to the shoot portion below the treated leaf than the tolerant lines. Metabolism of diclofop was more rapid at 30 than 10C; however, the three sunflower lines metabolized diclofop similarly.

Sweet corn (Zea mays L. rugosa 'Seneca Scout’) and soybeans (Glycine max L. Merr. ‘Kanrich’) were grown in nutrient solutions containing alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl)acetanilide] at 2.36 × 10-5 M, polyethylene glycol MW 6000 (PEG6000) at −2.5 bars osmotic potential, alachlor at 2.36 × 10-5 M plus PEG6000 at −2.5 bars osmotic potential or with no additions. Sweet corn and soybean roots exposed to alachlor plus PEG6000 accumulated significantly more PEG6000 than roots exposed to PEG6000 alone; increased shoot uptake occurred only in soybean. Alachlor was also shown to significantly increase root osmotic potential and decrease root electrolyte leakage.

GAF 141 [(2-chloroethyl)phosphonic acid plus N-methylpyrrolidone] increased basipetal translocation of glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-o-anisic acid), and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxyl]-2-nitrobenzoic acid} in bean seedlings (Phaseolus vulgaris L. 'Stringless Greenpod′). The GAF 141 was applied as a foliar treatment before or at the same time as herbicide injection into the cotyledonary node. GAF 141 applied 24 h prior to glyphosate, dicamba, or acifluorfen injection enhanced basipetal translocation to the roots and inhibited acropetal translocation to the young shoots. GAF 141 applied simultaneously with the herbicide injection did not have substantial effects on translocation. Greater basipetal translocation of acifluorfen occurred at high (75 ± 5%) than at low relative humidity (35 ± 5%).

Studies were conducted to test if dicamba reduces haloxyfop herbicidal activity and to determine if this interaction by auxin-type herbicides or bentazon was caused by preventing the haloxyfop-induced inhibition of acetyl-CoA carboxylase (ACCase). Addition of dicamba at concentrations of 2.17 or 4.34 mM reduced haloxyfop activity on tall fescue shoots. Haloxyfop at 14 to 20 μM inhibited the activity of ACCase in cell-free extracts from tall fescue by nearly 50%. Dicamba did not prevent the inhibitory effect of haloxyfop on ACCase activity in these cell-free enzyme preparations. Dicamba alone at concentrations as high as 3.2 mM had no significant effect on the in vitro activity of the enzyme. Bentazon concentrations up to 10 mM did not prevent haloxyfop inhibition of ACCase activity. Bentazon alone or mixed with haloxyfop significantly inhibited ACCase activity at bentazon concentrations starting at 1 mM with near 40% inhibition at 10 mM. of the numerous possible explanations for the interference of dicamba or bentazon with haloxyfop action, interaction directly at the enzyme level appears to have been eliminated.

Tebuthiuron was applied at 1 kg ai/ha to wet and dry Hathaway gravelly, sandy loam soil in the spring and fall to determine the amount of tebuthiuron removed in runoff water and the depth to which it would move within the soil profile by simulated rainfall. When pellets containing 20% ai of tebuthiuron were broadcast onto dry soil in the spring, the first simulated rainfall event, 37 mm, removed 5% of the applied tebuthiuron in runoff water and sediment. The second and third simulated rainfall events, 22 and 21 mm, respectively, removed an additional 2%. When tebuthiuron was applied to wet soil in the spring, the initial simulated rainfall events, totaling 42 mm, removed 15% of the tebuthiuron. When tebuthiuron was applied to wet soil in the fall, the initial rainfall events, totaling 40 mm, removed a total of 48% of the tebuthiuron in runoff water and sediment. No significant differences were found in the total amount of tebuthiuron within the soil profile after application to dry and wet soils. More than half of the tebuthiuron had moved into the surface 7 cm 1 day after application. Tebuthiuron was not detected below 90 cm after 165 mm of simulated rainfall and 270 mm of natural rainfall.

Preemergence and postemergence application of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one] at 0.6 and 1.1 kg ai/ha controlled downy brome (Bromus tectorum L. ♯ BROTE) in winter wheat (Triticum aestivum L. ‘McDermid’) but caused considerable injury without the use of activated carbon over the seeded row. Activated carbon applied in 5-cm bands over the seeded row at 84, 167, and 336 kg/ha protected winter wheat at Pendleton on a silt loam soil. On a sandy loam soil, only a 336 kg/ha rate provided protection from metribuzin. Metribuzin toxicity to winter wheat was more difficult to neutralize when applied preemergence. Downy brome control was not reduced by carbon applied over the wheat row. The best treatment in this study was carbon at 336 kg/ha applied preemergence over the row followed by metribuzin at 0.6 or 1.1 kg/ha postemergence. A 10-week delay between preemergence carbon banding and postemergence metribuzin protected winter wheat from chemical injury.

The persistence of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} both applied at 2.24 and 4.48 kg/ha was studied in the field on two soils. A greenhouse bioassay using cucumber (Cucumis sativus L. ‘Wisconsin SMR-18′) showed no reduction in growth when plants were grown in soil taken from cyanazine and atrazine treatments at the end of the season. Similarly, fall-sown rye (Secale cereale L.) was not injured. The yields of transplanted tomatoes (Lycopersicum esculentum L. ‘Campbell 28′) and transplanted watermelons (Citrullus vulgaris ‘Crimson Sweet’) were not significantly reduced when grown 1 yr after the initial application of either herbicide.

The allelopathic potentials of Hope white lupine (Lupinus albus L.) herbage and herbage extracts were evaluated. The emergence and growth of cotton (Gossypium hirsutum L. ‘Deltapine 45A’), soybean [Glycine max (L.) Merr. ‘Lee 68′], and six weed species under greenhouse conditions were measured after seeding directly into a moist, silt loam soil into which dry Hope lupine herbage, collected at second bloom, had been incorporated at rates from 500 to 8000 ppm (dry herbage/dry soil, w/w). At the lower rates, incorporated Hope white lupine stimulated the emergence of large crabgrass [Digitaria sanguinalis (L.) Scop.]; at the higher rates, cotton emergence was inhibited. Cotton and soybean fresh weights were stimulated at incorporation rates up to 2000 ppm, but were inhibited at higher concentrations. The growth of johnsongrass [Sorghum halepense (L.) Pers.] and large crabgrass was stimulated at most incorporation rates. Stimulated plants were chlorotic and had longer internodes. Emergence and growth of other species tested were not significantly affected by incorporated Hope white lupine. Equivalent concentrations of Hope white lupine herbage extracts were about 17 times more inhibitory to germination of cress (Lepidium sativum L. ‘Curlycress’) seed than to growth of sorghum [Sorghum bicolor (L.) Moench ‘AKS 663′] coleoptiles or radicles. The inhibitory principle extracted from Hope white lupine herbage was non-volatile, heat insensitive, and significantly less active in soil. Fractionation of a herbage extract suggested that neither the alkaloid nor phenolic acid content could account for herbage phytotoxicity in soil.

A study of herbicides to aid in establishing an Emerald zoysia (Zoysia japonica x Zoysia tenuifolia Willd. ex Trin.) sod was initiated in the summer of 1965. Eleven herbicides were applied to Emerald zoysia sod-plugs newly planted in Emory clay loam soil. All of the herbicides provided excellent premergence control of crabgrass (Digitaria spp.) and goosegrass (Eleusine indica (L.) Gaertn.) throughout the growing season following treatments. Both 1-(2-methylcyclohexyl)-3-phenylurea (siduron) and O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramido-thioate (DMPA) caused either no observable injury or only slight injury, thus causing no apparent chemical inhibition of growth and resulting in a rapid rate of establishment of the turfgrass. But N-(2-mercaptoethyl)benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide) and 2,6-di-tert-p-tolyl-methylcarbamate (terbutol) severely injured Emerald zoysia; they seriously retarded the growth of the zoysia and greatly inhibited ground cover. Herbicides which effectively eliminated weed competition but which greatly retarded the growth of the turfgrass were more detrimental to establishment rate than the actual competition from weeds. These results indicate that selecting a herbicide safe to the turfgrass is more important than choosing a herbicide which only gives good weed control. However, indications are that some herbicides do combine the two important factors of safety and excellent weed control.

Benthiocarb S-[(4-chlorophenyl) methyl] diethylcarboamothioate which was applied postemergence, altered the growth and development of shoots of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and bearded sprangletop [Leptochloa fascicularis (Lam.) Gray] seedlings, two gramineous annual weeds commonly found in rice fields. The herbicide did not affect root development of either species. Benthiocarb retarded the growth of new leaves within the extending leaves and caused swelling of cells. The cells of the shoot apices of treated seedlings were often vacuolated. Tubular-like leaves were induced by benthiocarb, but their formation differed from that caused by phenoxy herbicides.