The relative effectiveness of eight acetanilide herbicides for controlling annual weeds in processing peas (Pisum sativum L.) was evaluated in field studies and the susceptibility of peas to injury from these herbicides was studied in both the field and greenhouse. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was the most phytotoxic to peas grown in washed silica sand in the greenhouse when the herbicides were applied at concentrations of 2 and 8 mg/L. Field trials conducted over a 2-yr period and simulated rainfall experiments in the greenhouse demonstrated that the phytotoxicity to peas by acetanilide herbicides applied preemergence at 2.2 and 4.5 kg/ha was greatly influenced by subsequent rainfall. When 2.5 cm of simulated rainfall were applied immediately after herbicide application, pea injury increased. Injury to peas was avoided in the field by delaying alachlor application at 2.2 kg/ha until peas began to emerge. This treatment also gave excellent control of annual grass weeds. Greenhouse studies demonstrated that injury to peas by all eight acetanilide herbicides at 2.2 and 4.5 kg/ha could be avoided by delaying application until pea emergence. Alachlor, propachlor (2-chloro-N-isopropylacetanilide), and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] gave slightly superior weed control than butachlor [N-(butoxymethyl)diethylacetanilide] and H 22234 [N-chloroacetyl-N-(2,6-diethylphenyl)-glycine ethyl ester].

Biotypes of several annual broadleaved weeds tolerant to 2-chloro-s-triazines have been recorded, including common lambsquarters (Chenopodium album L.). The mechanism of resistance in common lambsquarter was based on the differential inhibition of the Hill reaction in chloroplasts by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Chlorophyll fluorescence and electron transport assays were used with isolated chloroplasts of atrazine-tolerant and susceptible biotypes, to determine the effect of atrazine and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on photosystem II (PS II) activity, differential atrazine penetration of the chloroplast envelope, and relative tolerance to chloro, methoxy, and methylthio triazines. Atrazine and diuron inhibited electron transport on the reducing side of PS II in susceptible biotype chloroplasts. In tolerant biotype chloroplasts only diuron inhibited electron transport whereas atrazine had only slight effects. There were no differences in the chloroplast membrane permeability to atrazine in the two biotypes. Chloroplasts of the atrazine-tolerant biotype of common lambsquarters were also tolerant to the other classes of triazines tested.

A 6-h imbibition in sodium azide solution stimulated nearly 100% germination of dormant wild oat (Avena fatua L.) seeds in petri dishes. Sodium azide stimulated germination in soil in both field and growth chamber experiments. Disc-incorporated sodium azide in soil at 11.2 kg/ha caused a 4-fold increase in wild oat emergence as 50% of the wild oat seeds in a natural infestation germinated compared to 12% in control plots. Wild oat seed germinated from greater soil depths following sodium azide application. Sodium azide appears to need a deep, thorough soil incorporation and adequate soil moisture for maximum stimulation of germination.

Field experiments were conducted on a Moody silty clay loam (pH 6.5) and a Crofton silt loam (pH 7.9) to evaluate the influence of soil texture and pH on metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] toxicity to soybeans [Glycine max (L.) Merr. ‘Amsoy 71’] as influenced by trifluralin [α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine]. One Crofton silt loam site contained atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] residue. Soybean growth and yield was not significantly affected by metribuzin and trifluralin applications on the Moody silty clay loam. On the Crofton silt loam without atrazine residue, substantial early season soybean injury from metribuzin did not result in significantly reduced soybean yield. Atrazine residue from previous row banding on corn (Zea mays L.) on the Crofton silt loam reduced soybean tolerance to metribuzin but normal use rates of 0.4 kg/ha metribuzin did not significantly reduce soybean yield. Trifluralin reduced early season soybean injury from metribuzin but this effect was not reflected in soybean yield. Metribuzin injury to soybeans was greater in years when more rainfall and cooler temperatures occurred following herbicide application. Metribuzin applied either preplant incorporated with or as an overlay on trifluralin resulted in equal soybean injury and yield.

The metabolism of three 14C-ring-labeled herbicides, atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], chloramben (3-amino-2,5-dichlorobenzoic acid), and dicamba (3,6-dichloro-o-anisic acid) was studied in the earthworm, Lumbricus terrestris L., taken from plots treated with these herbicides for the past 10 yr and from control plots treated with no herbicides. For the two benzoic acid herbicides, acetone extracts of sand and earthworms from untreated plots contained more unmetabolized herbicide than similar extracts of sand and earthworms from treated plots, indicating a net enhancement of metabolism in worms from treated plots. For atrazine, the amount of unchanged herbicide in the acetone extracts of earthworm and sand were nearly equivalent. Finally, the relative metabolic stability of the three herbicides in decreasing order in earthworms from both control and untreated plots was chloramben>atrazine>dicamba.

Seeds of 82 species of weed and crop plants were tested for germinability after dry storage or storage in fresh water for 3 to 60 months. Seeds of 24 species did not germinate after storage in water for 12 months or less; whereas some seeds of 27 species germinated after 60 months in water storage. When stored in water for longer than 12 months some seeds of only 22% of the annual monocots tested germinated; whereas about 75% of the perennial monocots, and annual and perennial dicots germinated. Species whose seeds consistently germinated better after water storage than after dry storage were western waterhemlock [Cicuta douglasii (DC.) Coult. & Rose], woolly sedge (Carex lanuginosa Michx.), pale smartweed (Polygonum lapathifolium L.), bouncingbet (Saponaria officinalis L.), and blue vervain (Verbena hastata L.).

Wild oat (Avena fatua L.) control and wheat (Triticum aestivum L.) injury with barban (4-chloro-2-butynyl m-chlorocarbanilate)-aqueous nitrogen combinations were evaluated in the field and greenhouse. The addition of aqueous nitrogen at volumes as low as 5 L/ha increased wild oat control with barban. The greatest increase in wild oat control with barban-aqueous nitrogen combinations was obtained on soil low in nitrogen. Wild oat control with barban-aqueous nitrogen combinations was not influenced by spray volume or nitrogen source. Aqueous nitrogen applications several days prior to barban were more effective than when the two were applied together. Wheat was generally quite tolerant of barban-aqueous nitrogen combinations; however, some injury was observed in 1974.

Key metabolic enzymes and germination were studied in developing and mature, dormant and nondormant prickly sida (Sida spinosa L.) seeds. Isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, fructose-1,6-diphosphatase, and phosphofructokinase activities were determined in developing and mature prickly sida seeds. Developing seeds less than 7 days after anthesis and at 17 days or greater after anthesis were unable to germinate. The 7-day-old seeds lacked all but fructose-1,6-diphosphatase activity. The 17-day-old seeds demonstrated all enzyme activities but failed to germinate because dehydration had occurred and seeds were unable to imbibe sufficient water without an afterripening period. Comparison of enzyme activities of dormant and nondormant seeds on incubation showed that only glucose-6-phosphate dehydrogenase was considerably different within the first 8 h of incubation. Nondormant seeds had considerable glucose-6-phosphate dehydrogenase activity before germination (radical protrusion at 8 h), suggesting an active pentose phosphate pathway.

In the greenhouse, the methyl ester of diclofop {2-[4-(2,4-diclorophenoxy)phenoxy] propanoic acid} as a postemergence application at 1.1 kg/ha ai did not affect the growth of the seven dicotyledonous crops with the exception of slight injury to yellow [white] mustard (Brassica hirta Moench). Of the 13 gramineous species, corn (Zea mays L.), green foxtail [Setaria viridis (L.) Beauv.], oats (Avena sativa L.) wild oats (Avena fatua L.), sorghum [Sorghum bicolor (L.) Moench], and timothy (Phleum pratense L.) were rated highly susceptible, while barley (Hordeum vulgare L.), bromegrass [smooth brome] (Bromus inermis Leyss.), durum wheat (Triticum durum Desf.), intermediate wheatgrass [Agropyron intermedium (Host) Beauv.], Russian wild ryegrass (Elymus junceus Fisch.), triticale (X Triticosecale Wittmack), and wheat (Triticum aestivum L.) were relatively tolerant. Residue of diclofop in the soil partially controlled green foxtail which was seeded 3 weeks after herbicide application. Whether applied to wild oat shoots or roots, diclofop affected the entire plant, but growth reduction was great when applied to the shoots. Field results confirmed that foliar application gave the best weed control resulting in larger wheat yield increases. Wild oat control was greatly enhanced when an adjuvant was added to diclofop. This enhanced herbicidal activity appeared to have no effect on tolerance of barley at 0.8 kg/ha nor wheat at 1.1 kg/ha. Increasing the temperature from 12 to 28 C decreased wild oat control from diclofop at 1.1 kg/ha. In the field, diclofop at rates ranging from 0.8 to 2.2 kg/ha gave good control of wild oats and green foxtail resulting in significantly increased wheat yield compared to the checks. However, barley yield increases were obtained only at the rates from 0.8 to 1.1 kg/ha, indicating that at the higher rates barley was less tolerant than wheat. The 0.6 kg/ha rate with an adjuvant gave adequate weed control and significant barley yield increases over the checks, when evaluated on five barley cultivars.

The absorption of 14C-dipropetryn (2-ethylthio-4,6-bis-isopropylamine-s-triazine) and 14C-prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] by roots of intact seedlings of corn (Zea mays L. ‘Iowa Chief) and oats (Avena sativa L. ‘Cimarron’) was very extensive and occurred to about the same degree in both species after application to the root medium. The translocation of 14C-label of dipropetryn to the shoots was low in corn as compared to oats. Prometryn 14C-label was more readily translocated to the tops of corn than dipropetryn and was more readily translocated in oats than corn. Dipropetryn 14C-label entered excised leaves through the transpiration stream during a short exposure period and translocated to a greater extent in oats than in corn. The 14C-label of dipropetryn became immobilized in excised leaves after about 4 h. The 14C-label of prometryn was initially more mobile in excised leaves of oats than corn. However, translocation of the 14C-label of prometryn continued in both species during 10 h of treatment and there was very little difference in the final distribution pattern. DNP (2,4-dinitrophenol) did not affect the distribution pattern of the 14C-label of dipropetryn or prometryn in corn after 10 h treatments.

A crop rotation of sorghum [Sorghum bicolor (L.) Moench] and soybeans [Glycine max (L.) Merr.] with various weed control treatments was conducted from 1968 to 1975 at Lincoln, Nebraska, in order to improve weed control in these two crops. Poor weed control during one growing season increased weed growth and decreased yields of succeeding crops. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 1.1 kg/ha on soybeans showed greater soil carryover toxicity to sorghum planted 12 months later than did atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 3.4 kg/ha on sorghum to subsequently planted soybeans. Under this crop rotation green foxtail [Setaria viridis (L.) Beauv.], tall waterhemp [Amaranthus tuberculatos (Moq.) J. Sauer], and large crabgrass [Digitaria sanguinalis (L.) Scop.] decreased; whereas, velvetleaf (Abutilon theophrasti Medic), sunflower (Helianthus annuus L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) increased. Germinating weed seedlings from soil samples were greater in weedy check plots during the final years of the crop rotation due to a buildup of seed from those species that increased. Handweeding, herbicides, and plowing reduced weed populations, weed competition, and increased sorghum and soybean yields.

Mature plants of tomato (Lycopersicon esculentum Mill. ‘Super Sioux’), cucumber (Cucumis sativas L. ‘Early pickling’), and pinto bean (Phaseolus vulgaris L.), in small field plots, were exposed once to sprinkler or furrow irrigation water containing 0.11 kg/ha or 1.12 kg/ha MSMA (monosodium methanearsonate). Concentrations of MSMA in water were about 0.22 ppmw and 2.2 ppmw for the two rates, respectively. Samples of crops and soil were subsequently analyzed for elemental arsenic content by colorimetric and atomic absorption methods. Arsenic residues were higher, compared to controls, only in crops exposed to MSMA applied in sprinkler irrigation. Average arsenic levels were highest in tomatoes exposed to 2.2 ppmw MSMA by sprinkler irrigation, and after 30 and 45 days were 0.26 ppm and 0.35 ppm, respectively. Average arsenic levels in sprinkler-irrigated crops ranged from double to triple the arsenic levels in control (untreated) crops. Atomic absorption was more sensitive than the colorimetric method and could detect smaller differences in arsenic content of samples. The average arsenic residues in soil varied from 1 to 3 ppm, but the differences could not be attributed to treatment with MSMA.

The translocation and effects of glyphosate [N-(phosphonomethyl)glycine] were determined in greenhouse-grown peach [Prunus persica (L.) Batsch] seedlings obtained from different seed parents. Two lower branches of 10-week-old seedlings of Rutgers Red Leaf, Bailey, Kalamazoo, Siberian C, and Harrow Blood were sprayed with 0.9 to 18 mg of glyphosate per plant. Seedlings of Harrow Blood, Bailey, and Kalamazoo were more susceptible to injury than were those of Siberian C and Rutgers Red Leaf. Glyphosate at 6, 9, and 18 mg produced necrotic areas on the stems of the former seedlings and at the higher rates tree death resulted. The Siberian C and Rutgers Red Leaf seedlings showed only chlorosis and malformation of apical leaves although slight stem injury occurred 1 month after treatment. Measurements of plant weight, height, and stem diameter indicated that seedlings of Harrow Blood, Bailey, and Kalamazoo tolerated only 3 mg of glyphosate without growth reduction. This was one-half and one-third of the amount which seedlings of Siberian C and Rutgers Red Leaf tolerated, respectively. The concentration of glyphosate in the treated lower branches and the main stem of the seedlings was determined by thin-layer chromatography. The concentrations in the bark were generally similar among all seedlings. Differential tolerance, therefore, was not based on differences in overall glyphosate concentration in tissues but on protective or resistance mechanisms present only in seedlings of Siberian C and Rutgers Red Leaf.

The absorption and distribution of 14C terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] and 14C-fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] in cotton (Gossypium hirsutum L. ‘SJ-1’) and snapbean (Phaseolus vulgaris L. ‘Tenderette’) seeds during germination was studied. Seeds of the susceptible snapbean absorbed larger amounts of both herbicides from soil than the resistant cotton seeds. The herbicides accumulated mainly in the seed coat of cotton which shed following emergence, with no translocation to the seedling leaves. In snapbean seeds the herbicides accumulated in the cotyledons, which served as a source for acropetal flow to the developing foliage of the young seedling.

Absorption and translocation of 14C-mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} in soybeans [Glycine max (L.) Merr. ‘Lee 68’], common cocklebur (Xanthium pensylvanicum Wallr.), and johnsongrass [Sorghum halepense (L.) Pers.] were evaluated under different environmental conditions with and without adjuvants. At a constant level of 40 or 100% relative humidity (RH), an increase in air temperature from 22 to 32 C resulted in a two- to three-fold increase in absorption and a four- to eight-fold increase in translocation of the 14C in soybeans following application to the second trifoliolate. At constant 22 or 32 C an increase from 40 to 100% RH resulted in less than a two-fold increase in absorption or translocation of 14C in soybeans. Autoradiograms indicated that movement of the 14C was primarily into leaves above the treated area. Translocation of 14C was significantly greater following application to the lower stem than to leaves. In common cocklebur, 14C absorption increased about three-fold at both 22 and 32 C with an increase from 40 to 100% RH following application to the second alternate leaf. At both levels of RH, absorption and translocation increased as the temperature was increased from 22 to 32 C. The addition of an adjuvant increased absorption and translocation in common cocklebur under all environmental conditions. When 14C-mefluidide was applied without an adjuvant to johnsongrass, absorption increased five- to six-fold at both 22 and 32 C as RH was increased from 40 to 100%. Translocation in johnsongrass was often affected less by variations in temperature than it was in soybeans or common cocklebur. The adjuvant increased absorption and translocation of the 14C-label of mefluidide in johnsongrass. The 14C-label accumulated primarily in the distal leaf of johnsongrass or in leaves above the treated area.

Root uptake and translocation of nitrofluorfen [2-chloro-1-(4-nitrophenoxy)-4-(trifluoromethyl)benzene] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] were measured in fababean (Vicia faba L.) and green foxtail [Setaria viridis (L.) Beauv.] plants, and metabolism was studied using fababean leaf discs and green foxtail leaf segments. Both herbicides were taken up readily from nutrient solution but translocation was limited. In fababeans, 4.6% of the nitrofluorfen label was translocated to the shoot as compared to 2.2% of the oxyfluorfen label. Less than 10% of the nitrofluorfen or oxyfluorfen taken up in vitro was metabolized after 24 h. This rate of metabolism would not likely influence the herbicidal action of either herbicide.

Greenhouse and growth chamber studies were conducted to determine the cause of previously observed differences in the effectiveness of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] when applied at various times of the day to velvetleaf (Abutilon theophrasti Medic). Leaves of velvetleaf moved rhythmically from a near horizontal day position to a near vertical night position with the tip of the blade pointed downward. Plants were sprayed with bentazon at various times of day. The amount of spray retained and the degree of control decreased as the leaves moved toward the vertical downward night position. This suggested that a major cause of the time-of-day effect with bentazon treatments on velvetleaf is variation in the amount of spray intercepted and retained as a function of varying leaf angles.

The germination of seeds (achenes) of milk thistle [Silybum marianum (L.) Gaertn.] was investigated. One month after harvest, milk thistle seeds had afterripening requirements related to germination temperature that limited germination to 10 to 20 C temperatures. The time required to satisfy afterripening requirements was dependent on germination temperature. Generally the higher the incubation temperature during germination, the longer the afterripening requirement (up to a maximum of 5 months). Once afterripening requirements were satisfied, milk thistle seeds germinated over a temperature range of from 0 to 30 C. Optimum germination occurred with 2 to 15 C 16-h cold periods alternating with 10 to 30 C 8-h warm periods. Emergence of milk thistle seedlings decreased with increased burial depth, but substantial emergence occurred from 8 cm. Germination on the surface of the soil or litter was greatly reduced compared to that with slight soil or litter coverage. Potassium nitrate (KNO3) added to the germination substrate at 1.0 mM enhanced the germination of milk thistle seeds at 2 and 5 C incubation temperatures.

After land was plowed in the spring and prepared for planting, yellow nutsedge (Cyperus esculentus L.) was allowed to develop to heights of 10 to 12 and 20 to 25 cm. Either glyphosate [N-(phosphonomethyl)glycine] or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was applied to emerged yellow nutsedge and other annual weeds at rates of 0.5, 1, 2, and 4 kg/ha. Half of the plots were double-disked 3 days after herbicide applications, and then all plots were planted with alfalfa (Medicago sativa L. ‘Cayuga’). Disking alone and application of glyphosate or paraquat alone did not satisfactorily control all weeds. However, the combination of a herbicide and disking controlled weeds enough to allow excellent establishment of alfalfa. In the year after establishment, the first cutting yields from the better combination treatments ranged from 3000 to 4400 kg/ha, which is normal for mid- to late-summer plantings in the region. Glyphosate was better than paraquat for control of grass weeds. Paraquat approached glyphosate in effectiveness when a supplemental disking treatment was added. Disking was as effective as the herbicide treatments for control of yellow nutsedge but not for control of broadleaf or annual grass weeds.