The uptake, translocation, and metabolism of 14C-alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] by germinating and emerged snap bean (Phaseolus vulgaris L.) seedlings were monitored under 16-h daylength (21 klux) comparing 16 C night/21 C Day and 27 C night/32 C day temperature regimes. Total uptake of 14C-alachlor by germinating snap beans was greater under the higher temperature, however, the compound was localized primarily in the roots where it was rapidly metabolized. At the lower temperature, the label was located in approximately equal amounts in all plant parts except cotyledons and significantly less of the alachlor was metabolized. Root uptake of 14C-alachlor and translocation of labeled compounds to the shoots were significantly greater under the higher temperatures. Approximately 60% of 14C-alachlor was shown to volatilize from a watchglass after 48 h at 27 C. After volatilization, uptake of 14C-alachlor occurred in adjacent snap bean plants in a closed system.

A technique is described for removing seed from soil samples. The soil was poured as a water slurry over 0.841 mm and 0.58 mm sieves. The retained seeds were placed in a laboratory seed blower which was adjusted to remove light debris and seed coats without embryos. The remaining seeds were separated, identified, and counted. The technique was used with a 2-yr study which monitored soil weed seed populations in three vegetable cropping systems.

Morphological and chemical characteristics of 11 warm season pasture weed species were defined. Goldenrod (Solidago altissima L.) was significantly taller and common ragweed (Ambrosia artemisiifolia L.) had the largest canopy diameter of the 11 species studied. Species ranged from 14 to 134 cm in height with canopy diameters of 25 to 70 cm. No direct correlation was found between individual leaf size and total leaf area. Macro- and micromineral content varied widely among species but all values obtained were considered high enough to meet the requirements of ruminant animals. Redroot pigweed (Amaranthus retroflexus L.) and horsenettle (Solanum carolinense L.) contained potentially toxic levels of nitrate. Five of the 11 species contained sufficient crude protein for ruminants and six of the 11 species were more than 50% digestible. Digestible energy values averaged 1.9 Mcal/kg for the 11 weeds evaluated.

The cucumber (Cucumis sativus L.) accession PI 390244 tolerated up to 0.56 kg/ha atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] whereas most cultivars and accessions were killed by 0.14 kg/ha. The possible mechanisms for tolerance were investigated by comparing growth rates, effects on photosystem II in isolated chloroplasts, and differences in uptake and translocation of 14C-atrazine between tolerant PI 390244 and the susceptible cultivar Marketmore 70. PI 390244 had significantly more leaf area than Marketmore 70, but less root biomass. Isolated chloroplast preparations from both cultivars were equally susceptible to the herbicide. Although PI 390244 absorbed more total 14C-atrazine, it translocated less radioactivity from the roots. While the concentration of 14C found in the PI 390244 roots was 10 to 30% greater than in Marketmore 70, the amount of radioactivity in the cotyledons, and first and second true leaves of Marketmore 70 were 53, 34, and 55% higher, respectively, after 48 h.

Lanolin or lanolin + corn (Zea mays L.) starch rings are often used as barriers on leaves to prevent runoff of foliarly applied 14C-herbicide treatments. A preliminary experiment showed that 64 and 90% of the applied 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 57 and 87% of the applied glyphosate [N-(phosphonomethyl)glycine] was adsorbed to or absorbed into a lanolin and lanolin + starch ring, respectively, during 6 days on a glass slide. Absorption and translocation of 2,4-D in hemp dogbane (Apocynum cannabinum L.) was decreased from 26% down to 16 or 17% of the total applied when a lanolin or lanolin + starch ring was used. Glyphosate absorption and translocation increased with the lanolin ring but not with the lanolin + starch ring. Distribution of the translocated 2,4-D and glyphosate was also altered by use of the ring barriers. Results indicate that one should avoid use of the lanolin ring in 14C-herbicide absorption studies to simulate field conditions.

Twelve sequential herbicide treatments were compared to cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), a standard treatment, for control of annual weeds in sugarbeets (Beta vulgaris L.) in three field experiments conducted from 1971 through 1977. At harvest, seven sequential treatments had less than 10 annual broadleaf weeds per 30 m of row, whereas there were 40 broadleaf weeds per 30 m of row for the cycloate treatment. Four of these sequential treatments had significantly higher root yields and net returns than the cycloate treatment. Dependent on the sequential treatment and year, tonnage was increased 7.3 to 20.3 t/ha, and net returns $150 to $515/ha above those with cycloate. The most effective sequential treatment for control of weeds was a preplanting mixture of 2.2 kg/ha of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] plus 1.7 kg/ha of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} followed by a postemergence mixture of 0,6 kg/ha each of desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] plus phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate). This sequential herbicide treatment increased root yields by an average of 20.3 t/ha and net returns by $515/ha above those with cycloate.

Seeds of five yellow foxtail [Setaria lutescens (Weigel) Hubb.] biotypes, collected from Connecticut, Iowa, Massachusetts, Pennsylvania and California, were tested for dormancy and germination characteristics. Seeds of the California biotypes, while dormant at time of dispersal, germinated readily following a 4-month after-ripening period in dry storage. California biotype seeds did not require stratification. The eastern biotypes also showed high initial dormancy. Prolonged dry storage (16 months) or stratification overcame this dormancy to varying degrees. All five biotypes germinated over the range of 15 to 35 C, but the California biotype exhibited much higher germination at 35 C than any eastern biotype. The California biotype germinated more rapidly, by 1 to 3 days, at any given temperature than the eastern biotypes. These differences in dormancy and germination requirements between the five biotypes are considered as evidence to support a hypothesis of genetically controlled, physiological differences between geographically separated biotypes.

Applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg/ha at the start of each growing season severely damaged established alfalfa (Medicago sativa L. ‘Beaver’) and reduced seed yield 32% over a 4-yr period. Dandelion (Taraxacum officinale Weber) populations were reduced but perennial sowthistle (Sonchus arvensis L.) increased in frequency. Dichlobenil (2,6-dichlorobenzonitrile) applied at 2.1 kg/ha controlled both dandelion and perennial sowthistle. Alfalfa was damaged initially but rapid recovery resulted in an increase in seed yield in 2 yr out of 4. Terbacil (3-tert-butyl-5-chloro-6-methyluracil) applied at 1.1 kg/ha also controlled dandelion and perennial sowthistle. No alfalfa damage was evident and seed yields were increased 34% over a 3-yr period. Seed yield increased 30% where asulam (methyl sulfanilylcarbamate) was applied at 4.5 kg/ha, but there was no visible effect on the growth of either alfalfa or weeds. Simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], propham (isopropyl carbanilate) + PCMC (p-chlorophenyl-N-methyl carbamate), pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide], and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], did not affect alfalfa seed production significantly, although simazine and diuron did reduce dandelion populations.

The effects of varying concentrations and duration of alachlor [2-chloro-2′,6′diethyl-N-(methoxymethyl)acetanilide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] treatment on root growth, cell division, and cell enlargement were studied. Peas (Pisum sativum L. ‘Alaska’) and oats (Avena sativa L. ‘Victory’) were treated from 0 to 48 h with concentrations ranging from 1 × 10-8 to 1 × 10-3 M of each herbicide. After 48 h, average growth rates were significantly inhibited at concentrations of 1 × 10-7 M alachlor and 5 × 10−8 M metolachlor, and 5 × 10−7 M alachlor and 1 × 10-6 M metolachlor for peas and oats, respectively. When growth inhibitions were examined across time at concentrations greater than these, the degree of growth inhibition was a function of both concentration and duration of treatment. Often the greatest decrease in growth occurred between 0 and 12 h. Mitotic indices of root tip squashes from pea roots and paraffin sections from oat roots were determined. There was a significant reduction in the mitotic indices of pea roots treated for 48 h with 5 × 10−6 M alachlor or 1 × 10-5 M metolachlor. After a 30-h treatment, the mitotic indices of oat roots were significantly reduced by 1 × 10−7 M metolachlor and 1 × 10−6 M alachlor. Significant inhibition of elongation of etiolated oat coleoptiles were observed at 5 × 10−6 M alachlor (27%) and 5 × 10−5 M metolachlor (30%). Inhibition of pea hypocotyl elongation did not occur at concentrations below 5 × 10−4 M. It was concluded that the growth inhibition of plants caused by alachlor and metolachlor results from both an inhibition of cell division and cell enlargement.

Several environmental and edaphic factors were monitored to determine their association with tolerance of seeded tomatoes (Lycopersicon esculentum Mill.) to diphenamid (N,N-dimethyl-2,2-diphenylacetamide). Injury increased with increasing soil pH and reduced temperature within 7 days of seeding in both field and growth chamber tests. The application of soluble fertilizer and diphenamid at planting acted synergistically to increase tomato injury. Prior to emergence of the tomato seedlings, 14C-diphenamid uptake was slight but increased with higher temperatures, while growth was inhibited at both low and high temperatures. Uptake and metabolism of 14C-diphenamid by plants in the cotyledon stage was not greatly affected by temperature or pH; however, translocation from the root to the shoot was reduced under low temperatures and high pH. These differences in translocation paralleled reported differences between tolerant and susceptible species, and may account for the increased diphenamid injury to tomatoes grown under stress conditions.

Of several herbicides tested on both monocotyledon and dicotyledon species, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] was found to be the most effective in reducing transpiration in corn (Zea mays L.) plants; a reduction of 40% occurred. It was established that diuron was the active component in reducing transpiration, and not the additives in the commercial formulation (Karmex) used in this study. Foliar applications of low concentrations (0.035 to 0.56 kg/ha) of diuron effectively reduced transpiration in both cultivars (Pioneer 3780A and Pride 1108) of corn plants, at all stages of growth tested (from 3- to 10-leaf stage). This effect of diuron on reduced transpiration occurred when the supply of water or nutrients to the corn plants was either limiting or non-limiting. The reduction of transpiration of corn plants after treatment also prevented the leaves from wilting and becoming senescent. This effect was persistent over 16 days. Diuron treatment increased the water efficiency of the plants and this effect was more pronounced when water was limiting. Compared to the control, the treated plants used up to 68% less water for each gram of shoot dry weight produced. The increase in water efficiency indicates that transpiration was reduced more than photosynthesis.

The response of tomato (Lycopersicon esculentum Mill. ‘Chico III’), jimsonweed (Datura stramonium L.), and velvetleaf (Abutilon theophrasti Medic.) to postemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applied after cloudy weather was determined by shading the plants artificially before field application of the herbicide. One day of 76% actual shade reduced the tolerance of tomato, jimsonweed, and velvetleaf to metribuzin, and 3 days of shade further reduced plant tolerance to the herbicide. The GR50 values showed that tomato was about 30 times more tolerant than jimsonweed and about 40 times more tolerant than velvetleaf to metribuzin. After 3 days of shade, 2 or 3 days of sunshine were required to return tomato to its full tolerance to metribuzin. After 3 days of cloudy weather, metribuzin applied at about 55% of the normal dose should control jimsonweed and velvetleaf. Weather conditions before postemergence applications of metribuzin will determine the appropriate timing of application and the herbicide dose.

Moist-chilled and freshly harvested seeds of redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria glauca (L.) Beauv.] were tested for germination responses to soil ammonium and nitrate. A controlled environment was used to simulate overwintering and germination conditions in the field. The results suggest that no alteration of weed germination behavior should be expected in the crop ecosystems studied if ammonium plus nitrification inhibitor replaces other fertilizer systems which result in substantial levels of nitrate in the soil solution. The only germination effect was one of nitrate on unchilled foxtail. Chilling lowered catalase activity in both species.

Spring establishment of tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31’) is preferred over fall for turfs in Nebraska. Siduron [1-(2-methylcyclohexyl)-3-phenylurea] is commonly used for weed control in spring-seeded tall fescue. Siduron application rates of 6.8, 13.6, 27.2, and 40.8 kg/ha were compared with an untreated control in this study. All siduron applications reduced stand development. The 6.8 kg/ha rate nearly doubled the number of days for seedling emergence. Abnormal seedlings increased with increasing application rates and percent germination decreased with increasing rates. Tiller number declined at rates of 13.6 kg/ha and above. Plants treated with 6.8 kg/ha were 1.3 cm shorter than those growing in the untreated control. Plant and root dry matter production decreased with increasing application rates. Root weight was reduced more than plant weight. Degree of wilting and drought injury increased at 13.6 kg/ha. Water use declined with increased siduron application rates. The amount of water lost before wilting occurred also declined as siduron application rates increased. High temperature injury on seedlings was reduced with increasing rates of siduron. Reduction in high temperature injury was significantly correlated (r = 0.98) to reduced plant tissue moisture.

Absorption and translocation of the growth regulator 14C-chlorflurenol (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) and of the herbicide 14C-dicamba (3,6-dichloro-o-anisic acid) were studied in Canada thistle [Cirsium arvense (L.) Scop.]. Also investigated was how foliar treatments with chlorflurenol affected leaf uptake and distribution of dicamba by Canada thistle. Plants were grown in aerated nutrient solution. 14C-chlorflurenol showed strong acropetal and weak basipetal movement. Thirty-two percent of the foliar applied 14C-dicamba was absorbed and most of the radioactivity tended to accumulate in the young growing leaves. Only 0.6% of the applied radioactivity moved to the roots. Leaf absorption and basipetal translocation of 14C-dicamba were increased two- and ten-fold, respectively, by the simultaneous addition of chlorflurenol at 0.6 kg/ha. Root bud activity was increased when 4-week-old Canada thistle plants were foliarly treated with chlorflurenol at 0.6 kg/ha. Field work demonstrated that Canada thistle control could be enhanced by chlorflurenol addition to dicamba.

A sprinkler system was developed that applied water to quadrant-shaped plots with a uniformity coefficient greater than 90% for any 2-m zone between 3 and 9 m from sprinklers that were located at the vertex of the quadrant. With this sprinkler system, many variables that affect the performance and behavior of herbicides applied in irrigation water can be studied. When applied through this sprinkler system in 1.4 cm of water, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.3 kg/ha, EPTC (S-ethyl dipropylthiocarbamate) at 3.3 kg/ha, EPTC + trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 3.3 + 0.6 kg/ha, and EPTC + oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) at 3.3 + 0.8 kg/ha controlled barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), and hairy nightshade (Solanum sarachoides Sendt.) selectively in beans (Phaseolus vulgaris L. ‘Pinto 114’).

The responses of whitebrush (Aloysia lycioides Cham.) and several associated species to herbicides were evaluated in the Central Basin and South Plains of Texas. At Llano, hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], picloram (4-amino-3,5,6-trichloropicolinic acid), and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} were the most effective herbicides for whitebrush control. Picloram was the most effective herbicide on Lindheimer pricklypear (Opuntia lindheimeri Engelm.), tasajillo (Opuntia leptocaulis DC.), Texas colubrina [Colubrina texensis (Torr. & Gray) Gray], and Texas persimmon (Diospyros texana Scheele). Hexazinone, karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], and tebuthiuron controlled live oak (Quercus virginiana Mill.). Tebuthiuron pellets were slightly more effective on whitebrush when applied broadcast than when applied in rows 1.8 to 6.0 m apart. Roller chopping alone did not kill whitebrush nor improve effectiveness of tebuthiuron but did improve access to the land and visibility for 3 yr. Picloram applied either as the undiluted liquid formulation or as granules was the most effective herbicide for controlling a spectrum of species, including whitebrush. Picloram pellets were generally more effective on Lindheimer pricklypear and Texas persimmon when applied broadcast than when applied in rows. However, tebuthiuron was the most effective herbicide on blackbrush acacia (Acacia rigidula Benth.) and huisache [Acacia farnesiana (L.) Willd.], especially when applied in rows rather than broadcast.

Six substituted dinitrobenzamine herbicides, including butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), were evaluated as directed broadcast sprays applied and soil incorporated at time of last cultivation (layby) of cotton (Gossypium hirsutum L. ‘Acala SJ-2’). At the rates used, all herbicides provided more than 90% control of annual grasses. During 1976 and 1977, control of redroot pigweed (Amaranthus retroflexus L.) and smooth pigweed (Amaranthus hybridus L.) ranged from 90 to 100% and none of the herbicides differed significantly in their effect. However in 1975, butralin at 1.1 kg/ha did not improve pigweed control when compared to the untreated control. None of the herbicides consistently controlled black nightshade (Solanum nigrum L.) and except pendimethalin, none caused detectable cotton injury. In 2 of 3 yr, pendimethalin caused enlarged growth of the cotton stem in the cotyledonary node area contacted by the herbicide spray. Stem breakage following wind occurred in about 5% of the cotton plants; however, the injury was not manifested by reduced yield. None of the herbicides influenced cotton yield. Residues from soil samples collected 4 months after herbicide application reduced growth of Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Link) Wright]3 and grain sorghum [Sorghum bicolor (L.) Moench] 24 to 49%.

A study of the C4 plant itchgrass (Rottboellia exaltata L.f.) grown under 100%, 60%, 25% and 2% sunlight revealed differences in the anatomy and cytology of the foliar mesophyll and vascular bundles associated with shading. In the bundle sheath, shading caused a reduction in thickness of the cell walls, shrinkage of plastids, rearrangement of plastid thylakoids, a reduction in starch deposits and vacuolization of the cytoplasm. In general, plastids and mitochondria retained membrane integrity but underwent stromal deterioration. Shading effects on cytoplasm were similar for mesophyll and bundle sheath cells. Mesophyll chloroplasts lost starch grains and the peripheral reticulum tended to decrease with greater shading. Grana were well developed at all irradiances, although the chloroplasts themselves decreased in size with shading. Movement of mesophyll chloroplasts away from bundle sheath-mesophyll borders was pronounced at 60% sunlight and was progressively greater at the two lower irradiances. These observations suggest that the structural relationships thought to be necessary for the intercellular transfer of C4 acids and the functioning of the C4 photosynthetic pathway were disrupted by shading.

Two methods of obtaining air samples were used over 4-month periods in 1976 and 1977 to quantitate trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) vapors arising from a silt loam. With the first method, only the air from an enclosure covering 0.37 m2 of soil was sampled. The second method used air probes to sample the air above the field. Rainfall and resultant soil moisture were related to trifluralin vaporization from field soil. Soon after trifluralin incorporation (0.84 kg/ha) and, while the soil was relatively dry, there was very little herbicide vaporization. Trifluralin vapors accumulated rapidly during a period in which several centimeters of rain fell, but with continued precipitation the vapor density declined. The influence of rainfall and resultant soil moisture upon vaporization became less apparent as the soil concentration of the herbicides declined. Less than 0.5% of the applied trifluralin was detected as vapors during each 4-month period.