Field and greenhouse experiments were conducted to observe and measure the phytotoxicity of glyphosate [N-(phosphonomethyl)glycine] to potatoes (Solanum tuberosum L. ‘Russet Burbank’) applied at different stages of growth and to determine if glyphosate was translocated into the original mother tuber (seed piece) prior to initiation of daughter tubers. Glyphosate injury symptoms appeared 1 day after treatment and at least 50% of the foliage was necrotic within 7 days. Significant decreases in plant height, shoot and root dry matter content, and daughter tuber production were recorded at the 0.28- and 0.56-kg/ha rates. Higher rates of 1.12 and 2.24 kg/ha did not give further significant reductions. Maximum levels of 14C activity accumulated in all plant parts 4 days after application of the 14 C-glyphosate. The 14 C-glyphosate accumulated primarily in the apical meristem and roots. Extremely low levels of 14 C activity were detected in the mother tuber regardless of plant age when treated. Phytotoxic effects on the eyes of the mother tuber increased in severity with increasing rates of glyphosate as evidenced by abnormal sprouting.

Absorption experiments were conducted with tomato (Lycopersicon esculentum Mill. ‘VF-315’) seedlings using salts at the approximate ratio found in saline irrigation water (NaCl 41.9 mM, CaCl2 20.9 mM, and MgCl2 · 6H2O 10.5 mM) in combination with two herbicides. The osmotic pressure of this salt solution is 0.40 MPa (mega Pascal), which is equivalent to 4.0 bar or about 4.0 atm. EPTC (S-ethyl dipropylthiocarbamate) at 0.25 mM reduced the residual Na+, Ca2+, and Mg2+ content relative to the treatment with salts alone. CDEC (2-chloroallyl diethyldithiocarbamate) at 0.1 mM produced similar effects for Na+ and Ca2+. The addition of salts to either EPTC or CDEC induced significantly higher concentrations of total and residual herbicide in the tomato seedlings. The data suggest that salts reduce the tolerance of tomato to EPTC and CDEC by increasing absorption of the herbicides. The residual EPTC or CDEC in the tomato seedlings increased as the CaCl2 concentrations increased in the incubation medium. A strong linear relationship was found between the calcium content and EPTC or CDEC content in the tomato seedling tissue.

Visible wheat (Triticum aestivum L.) injury, delay in bloom date, and yield reduction were observed following herbicide treatments in growing wheat. Protein content and volume weight of winter wheat were not significantly affected by any herbicide treatment. Some treatments reduced annual grass and broadleaf population by 90% or more 6 weeks after spraying and maintained weed control 8 weeks in untilled winter wheat stubble. Effective herbicide treatments that caused the least winter wheat injury in 1977 and 1978 included metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] + alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 0.3 + 2.8 kg/ha, metribuzin + oryzalin (3,5-dinitro-N4,N4-dipropylsufanilamide) at 0.3 + 1.8 kg/ha, metribuzin + pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at 0.3 + 2.2 kg/ha, metribuzin + SN-533 [N-ethyl-N-propyl-3-(propylsulfonyl)-1H-1,2,4-triazole-1-carboxamide] at 0.3 + 0.8 kg/ha, and R-40244 [1-m-trifluoromethylphenyl)-3-chloro-4-chloromethyl-2-pyrrolidone] at 1.1 kg/ha. Herbicide treatments that showed the most potential to control annual grass and broadleaf weeds selectively in tillered winter wheat and stubble in 1978 include metribuzin + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 0.3 + 2 kg/ha, metribuzin + oryzalin at 0.3 + 1.4 kg/ha, and metribuzin + pendimethalin at 0.3 + 2 kg/ha.

Tomatoes (Lycopersicon esculentum ‘Roma VF’) and weeds were seeded at two locations in 1973 and 1974. In separate plots, jimsonweed (Datura stramonium L.), tall morningglory [Ipomoea purpurea (L.) Roth.], and common cocklebur (Xanthium pensylvanicum Wallr.) seedlings were thinned to densities ranging from 2.7 to 86 plants/m2. Densities of large crabgrass [Digitaria sanguinalis (L.) Scop.] ranged from 11 to 430 plants/m2. There were a few instances of difference in nutrient concentrations in tomato and weed leaf tissue, but no clear relationship was evident between concentration of N, P, K, Ca, Mg, and S and weed density. Considerably more fruit weight was produced per kilogram of total assimilated N, P, and K in the weed-free than in the weed-infested tomato plots.

The short-run economic consequences of bans on herbicides commonly applied to corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] on a typical Indiana farm were analyzed. A dinitroaniline ban reduced soybean yields and net farm income 17 and 32%, respectively. A triazine ban reduced corn and soybean yields 3 and 20%, respectively, and net farm income by 38%. A simultaneous ban on all dinitroaniline, triazine, and amide herbicides reduced corn and soybean yields 14 and 17%, respectively, and net farm income by 65%. Harvest delays attributable to less effective weed control resulted in a loss in efficiency, yields, and profits, and increased machinery and labor requirements. Hence, herbicide bans under typical Indiana conditions would inflict substantial, short-run economic losses on individual farmers. This study did not measure any potential public benefits or costs of herbicide bans, however.

A simple and quick method is described for identifying biotypes of common groundsel (Senecio vulgaris L.), common lambsquarters (Chenopodium album L.), and smooth pigweed (Amaranthus hybridus L.) that are resistant or susceptible to triazine herbicides. Leaf discs (3 mm diam) from the tested plants were vacuum infiltrated with a phosphate medium and exposed to a 3-klux light source. When 1.0 × 10−5M and higher levels of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) were present, the leaf discs from susceptible biotypes failed to float to the surface, whereas the leaf discs from resistant biotypes floated within 1 h. The urea herbicide, fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] inhibited the floating of leaf discs from both the triazine-susceptible and triazine-resistant biotypes. This method can be used to evaluate large numbers of plants to determine if they are resistant or susceptible to triazines without destroying the plants or preventing seed production.

In greenhouse studies, the American strain of Striga gesnerioides (Willd.) Vatke, indigo witchweed, was potted with a wide range of potential hosts, including some known to be parasitized by this species elsewhere, and with agricultural and ornamental crops of importance in the southern United States. The host range of the indigo witchweed was very limited and no major crop species were seriously affected. Based on these host studies, it appears that indigo witchweed poses little danger to American agriculture. Other strains of the parasite were likewise shown to be host specific.

The distribution patterns of several herbicide formulations sprayed on adaxial leaf surfaces were determined using scanning electron microscopy coupled with cathodoluminescence and x-ray microanalysis. The sodium and amine salts of MCPA {[(4-chloro-o-tolyl) oxy] acetic acid} sprayed on sugar beet (Beta vulgaris L.) leaves appeared as discrete deposits above the anticlinal cell walls that represented the location of spray drops that adhered to the leaf. When the sodium salt was applied to bermudagrass [Cynodon dactylon (L.) Pers.], the pattern of distribution was the same; however, each deposit was significantly smaller. The iso-octyl ester of MCPA coalesced into numerous, small, thick deposits on the cuticle of sugar beet leaves. The distribution of a wettable powder formulation of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino-s-triazine] appeared as uniform deposits over the anticlinal and periclinal cell walls that represented the location of aqueous spray drops after application. When a flowable formulation of atrazine was applied, there was a significant preferential accumulation of the herbicide at the edges of the separate deposits. One commercial formulation of propanil (3′,4′-dichloropropionanilide) yielded deposits that were crystalline, one that was partially crystalline, and one that was noncrystalline.

Napropamide [2-(α-napthoxy)-N,N-diethylpropionamide] inhibited root and shoot growth in corn (Zea mays L. ‘NC+ 59’) and tomato (Lycopersicon esculentum Mill. ‘Niagara VF315’) seedlings. Shoot growth was reduced less than root growth in both species. Corn roots were approximately 10 times more sensitive to napropamide than were tomato roots. Translocation of napropamide from the roots to the shoot of tomato occurred within 0.5 h and followed an apoplastic pattern. Little movement of napropamide from the roots to the shoots occurred in corn. Metabolism of napropamide was not evident in either species during an 8-h exposure. Absorption studies showed that total napropamide levels were 60% higher in corn root tissue than in tomato root tissue. The greater napropamide content in the corn roots was associated with a tightly bound fraction of the total napropamide influx.

Effects of 16 herbicides representing 14 herbicide classes on growth and extractable phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) were examined in light- and dark-grown soybean [Glycine max (L.) Merr. ‘Hill’] seedlings. High purity (96 to 100%) herbicides were supplied via aqueous culture at various concentrations: 0.5 mM amitrole (3-amino-s-triazole), 0.1 mM atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], 0.07 mM diclofop-methyl {methyl ester of 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoicacid}, 0.5 mM DSMA (disodium methanearsonate), 0.2 mM fenuron (1,1-dimethyl-3-phenylurea), 0.05 mM fluridone {1-methyl-3-phenyl-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, 0.5 mM MH (1,2-dihydro-3,6-pyridazinedione), 0.5 mM metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], 1.8 μM nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], 0.5 mM norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], 0.05 mM paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), 0.15 mM perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide}, 0.2 mM propanil (3′,4′-dichloropropionanilide), 0.1 mM propham (isopropyl carbanilate), 0.5 mM TCA (trichloroacetic acid), and 0.05 mM 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Dark-grown soybean seedlings (3-day-old) were transferred to control solutions (2 mM CaSO4) or to herbicide solutions (in 2 mM CaSO4) and grown at 25 C in continuous white light (200 μE•m-2•s-1) or continuous darkness until harvested 24 or 48 h after transfer. After 48 h, growth (fresh weight, dry weight, elongation) was inhibited by most of the chemicals. Other signs of toxicity (necrosis, secondary root stunting, and root tip swelling) were noted for some treatments. Roots were most affected, although hypocotyls were generally not changed. Hypocotyl elongation was stimulated by atrazine, fluridone, and norflurazon after 48 h light. Extractable PAL activity from soybean axes was decreased by atrazine, fenuron, metribuzin, norflurazon, propanil, propham, and 2,4-D. Amitrole and paraquat were the only herbicides that increased extractable PAL activity. Other compounds tested had no effect on the enzyme. None of the herbicides significantly affected in vitro PAL activity.

Several herbicides were sprayed on emerged London rocket (Sisymbrium irio L.), common sunflower (Helianthus annuus L.), ragweed parthenium (Parthenium hysterophorus L.), annual sowthistle (Sonchus oleraceus L.), and onion (Allium cepa L. ‘yellow granex PRR’), to determine selectivity. Onion yields were reduced with common sunflower and London rocket interference within 7 weeks after emergence. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] at 2.2 kg/ha controlled all but common sunflower under most field conditions and reduced the yield of onion in one experiment out of six. Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) reduced the yields of onion in two of four experiments and three of six experiments, respectively. Both herbicides controlled most weed species, but only bromoxynil controlled annual sunflower adequately. Onion was injured when low temperature, low light intensity, and high relative humidity occurred within 3 days of the application of herbicides. Bioassays showed that oxadiazon persisted 5 months in soil in three of five experiments. Seeded London rocket populations reduced the growth of onion 20% within the first 4 weeks and 65% within 12 weeks after planting.

The uptake and translocation of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} were examined in sago pondweed (Potamogeton pectinatus L.) and Richardson pondweed [Potamogeton richardsonii (Ar. Benn.) Rydb.]. Root and shoot tissues of both species were isolated from each other with wax barriers and treated individually with 1.0 ppm 14C-fluridone. Both tissues bioconcentrated fluridone, but the amount absorbed represented 1% or less of the total herbicide available. Limited root-to-shoot translocation occurred, but shoot-to-root transport was negligible. In contrast to fluridone, highly mobile glyphosate [N-(phosphonomethyl) glycine] translocated from the shoots to the roots in sago pondweed. No metabolism of fluridone was detected in sago pondweed.

Experiments were conducted using the Avena coleoptile straight-growth test to determine the influence of diclofop {2-[4-(2,4-diclorophenoxy)phenoxy] propanoic acid}, as the acid or methyl ester, and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} on coleoptile growth of several species. Diclofop ester was a three-fold stronger inhibitor of oat (Avena sativa L. ‘Terra’) coleoptile growth than the free acid. The concentration of diclofop ester needed to inhibit 50% of the oat coleoptile growth was not influenced by IAA (indole-3-acetic acid) concentration. Oat coleoptile growth in the presence of 5 μM IAA plus 5 μM diclofop ester increased for 2 h after treatment and then decreased, so that the coleoptile length was less at the end of the 24-h assay period than at the beginning of the diclofop-ester treatment. Diclofop ester inhibited the coleoptile growth of wild oat (Avena fatua L.) > oat > wheat (Triticum aestivum L. ‘Era’) > corn (Zea mays L. inbred ‘A-239’) > corn inbred ‘CI-66’. MCPA added to the treatment solution did not overcome oat coleoptile growth inhibition from diclofop ester or acid.

Different Saskatchewan soils were studied to determine their populations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] degraders and gross aerobic bacteria. Soil from Indian Head field plots receiving relatively high field rates (1.12 or 1.68 kg/ha) of 2,4-D amine or ester applied annually over the previous 32 yr contained the highest population of degraders, ranging from 103 to 104 degraders/g soil. Control plots recorded lower populations of degraders (2.5 ± 0.5 × 103 degraders/g soil). Five soils from around the province were also studied, and a relationship was found between the rate of breakdown of 14C-2,4-D in the soil and the number of degraders. Another soil from a different site at Indian Head, but of a similar type to that in the field plots, displayed a much slower rate of 2,4-D degradation and also a much lower degrader population (7 ± 2 degraders/g soil) when compared to the other four soils (4 × 102 to 9 × 102 degraders/g soil). The ratio of degraders to the total bacterial flora varied in all studies between 1:6.5 × 102 and 1:3 × 105. When 1030 soil isolates were screened for their ability to degrade 2,4-D using an agar-block extraction technique, none possessed this feature. This would support the hypothesis that the ratio of 2,4-D degraders to the total microbial flora was indeed large (at least 1:103).

The application of 2,4-D [(2,4-dichlorophenoxy) acetic acid], at 1.1 kg/ha to common dandelion (Taraxacum officinale Weber) resulted in 40% or less survival in lawn and hayfield habitats, in both spring and fall treatments. A significantly lower incidence of regeneration (12 to 20%) was attained independent of the season by shoot removal (spudding) combined with 2,4-D in the lawn, but not in the hayfield habitat. No measure of control was obtained by spudding alone, confirming the high capacity of common dandelion for root regeneration. Removal of leaves 2 weeks after application of 2,4-D diminished the effectiveness of control in both lawn and hayfield habitats, with 49 to 50% and 60 to 70% regeneration, respectively. Apparently, there is incomplete translocation of the herbicide within this interval. Significant mortality from spudding alone was observed only in plants less than 4 months old (64% survival). One-year-old plants responded to all treatments in the same manner as common dandelion populations as a whole. Optimum control of common dandelion in lawns was obtained by 2,4-D application in combination with spudding, during the spring.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] applied with simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] reduced by 47 to 82% the severity of simazine symptoms on California privet (Ligustrum ovalifolium Hassk.), staghorn sumac (Rhus typhina L.), and ‘Moonlight’ broom (Cytisus X praecox Bean). Oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) had a similar but smaller effect (40% reduction) when applied with simazine on broom in a field experiment and an effect equal to napropamide with simazine on privet in a greenhouse experiment. Both napropamide and oryzalin prevented some of the growth reduction from simazine on privet, broom, and ‘Baltic’ ivy (Hedera helix L. ‘Baltica’) in field experiments. In the greenhouse study with privet, napropamide prevented much of the growth-reducing effects of simazine on both shoots and roots of privet. Oryzalin appeared to have a similar effect.

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] applied postemergence in November at rates from 1.4 to 4.5 kg/ha eliminated all annual bluegrass (Poa annua L.) that had survived application of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in fall carbon-planted perennial ryegrass (Lolium perenne L.) seed fields. Ethofumesate also eliminated all annual bluegrass in established perennial ryegrass seed fields when applied in late October at rates from 1.1 to 3.4 kg/ha or when applied as sequential treatments with atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 1.4 kg/ha or with simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 2.2 kg/ha. In most experiments, perennial ryegrass seed yields were not adversely affected by applications of ethofumesate alone or by sequential treatments with diuron, atrazine, or simazine.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] has considerable potential for yellow nutsedge (Cyperus esculentus L.) control in crops commonly produced in the Texas High Plains. Little information is available, however, concerning adsorption characteristics of metolachlor in soils of this region. Adsorption and movement of metolachlor were determined in three commonly occurring soils of the Texas High Plains. Organic carbon contents of the soils by weight varied from 0.3 to 0.5%, and the clay fraction ranged from 16 to 33%. Freundlich adsorption isotherms exhibited two linear regions for each soil, suggesting the possibility of multilayer adsorption. K′oc values and coefficients of determination for organic carbon and clay content vs. Freundlich K values indicated that organic matter was the predominant adsorbent for metolachlor in the soils studied. Desorption, soil column leaching, and thin-layer plate studies demonstrated metolachlor to be sufficiently mobile in scils low in organic matter to cause possible crop injury or loss of efficacy.

Glyphosate [N-(phosphonomethyl)glycine] toxicity to bermudagrass [Cynodon dactylon (L.) Pers.] increased as 0.84 kg/ha of the herbicide was applied in decreasing volumes of diluent from 374 to 47 L/ha. Visible injury to bermudagrass varied from 18 to 91% depending upon the spray solution formulation and diluent volume. The addition of surfactant to glyphosate (MON 0139) formulated without surfactant increased bermudagrass injury at each diluent volume tested. Glyphosate commercially formulated with surfactant (MON 2139) was the most toxic of the three formulations to bermudagrass. Regrowth of bermudagrass clipped at the soil surface 48 h after treatment ranged from 10% of the untreated control with MON 2139 at 47 L/ha to 100% of the control with MON 0139 at 374 L/ha. The MON 2139 formulation showed as much as a six-fold increase in foliage regrowth when the diluent volume was increased from 47 to 374 L/ha.

The fate of foliarly applied 14C diclofop-methyl {methyl 2-[4-(2,3-dichlorophenoxy)phenoxy] propanoate} was determined in intact plants of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], a susceptible (S) grass; proso millet (Panicum miliaceum L.), a moderately susceptible (MS) grass; longspine sandbur [Cenchrus longispinus (Hack.) Fern.], a tolerant (T) grass; soybean [Glycine max (L.) Merr. ‘Hark’], and cucumber (Cucumis sativus L. ‘Green Star’), both T broadleaf plants, 1,3, and 5 days after treatment (DAT). Diclofop-methyl accounted for 94% of the radioactivity washed from the leaf surfaces of all species. Plant extracts contained diclofop-methyl, diclofop, and water-soluble conjugates. Barnyardgrass (S), proso millet (MS), and soybean (T) had 75, 68, and 66% of the extracted radioactivity as diclofop and diclofop-methyl. Longspine sandbur (T) and cucumber (T) had 71 and 84% of the extracted radioactivity as water-soluble conjugates. Acid hydrolysis of the water-soluble conjugates yielded 84 and 71% diclofop in barnyardgrass (S) and proso millet (MS). Cucumber (T), soybean (T), and longspine sandbur (T) had 43, 23, and 25% ring-OH diclofop. Alkaline hydrolysis of the non-extracted plant residue yielded diclofop as the major component in all species.