Various levels of intraspecific competition influenced johnsongrass [Sorghum halepense (L.) Pers.] reproduction. Increases in density, from one to eight plants per 20-cm pot, delayed for formation of rhizomes and panicles and reduced the final dry weight accumulation in these reproductive structures under greenhouse conditions. Tillering was delayed by medium density (4 plants per pot) and inhibited by the highest density (8 plants per pot). At all densities, the dry weight accumulation in reproductive structures was associated with a decrease in dry weight of the shoot material. Most of the reproductive effort was in the formation of rhizomes rather than panicles. Crowding of johnsongrass plants delayed the formation of the reproductive structures and reduced their final dry weight.

The abilities of herbicides to either produce superoxide radical or react with this radical were examined. The effect of the herbicides on the superoxide-induced reduction of p-nitro blue tetrazolium chloride was used as an index. Paraquat (1,1-dimethyl-4,4′-bipyridinium ion) enhanced and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] inhibited the reduction of p-nitro blue tetrazolium chloride. Paraquat was reduced photochemically (riboflavin/methionine) or enzymatically (xanthine/xanthine oxidase) and produced superoxide radical upon reoxidation. Diuron and monuron [3-(p-chlorophenyl)-1,1-dimethylurea] interacted with photochemically produced superoxide radical, but not with enzymatically produced superoxide radical. The product of the monuron/superoxide interaction was a demethylated, dechlorinated, water-soluble compound containing phenolic hydroxyl group(s), and was not toxic to oats (Avena sativa L.). The enzyme superoxide dismutase prevented the formation of this product.

The degradation and leaching of methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and metabolites in Elmwood sandy loam soil over time in response to average spring environmental conditions was studied by using soil columns placed on a rainfall simulator in an environmental growth chamber. Methazole was degraded to 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3-(3,4-dichlorophenyl) urea (DCPU) over a 6-week period following methazole application, during which the soil columns received simulated rainfall of 1.27 cm every fourth day. Methazole level decreased to 27% of the original amount while DCPMU and DCPU levels increased to 53% and 1%, respectively. Of the total radioactivity remaining in the soil columns after 44 days and after 14 cm rainfall, approximately 80% remained above a depth of 6.35 mm.

Several experiments were conducted to determine the influence of temperature, relative humidity, leaf age, and additives on 14C-bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] uptake and translocation by redroot pigweed (Amaranthus retroflexus L.), wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] and soybeans (Glycine max L. Merr. ‘Corsoy’). A water soluble linseed oil formulation enhanced absorption and translocation of the 14C-label by redroot pigweed more than did emulsifiable linseed oil, petroleum oil, or a surfactant. The oil additives reduced the 14C-label washed from the treated area of a leaf and increased absorption and translocation compared to bentazon applied alone. Low relative humidity and older leaves of redroot pigweed resulted in less 14C-bentazon absorption than with high relative humidity or younger leaves. The addition of emulsifiable linseed oil reduced the influence of low relative humidity and leaf age upon 14C-bentazon absorption. Comparative absorption and translocation of 14C-bentazon was wild mustard > redroot pigweed > soybeans. Uptake and translocation of 14C-bentazon by redroot pigweed was greater at 30 C than at 10 C.

Studies were conducted to determine the effect on absorption and metabolism of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] by atrazine-susceptible (S) and -resistant (R) biotypes of common lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.). The response of isolated chloroplasts of susceptible and resistant biotypes of each species was also studied. In both species the two biotypes absorbed atrazine equally well and were unable to differentially metabolize the herbicide. The photochemical activity of R chloroplasts isolated from each species was not inhibited by atrazine but S chloroplasts were severely inhibited.

The capacity for photosynthetic acclimation to light intensity in Sakhalin knotweed (Polygonum sachalinense F. Schmidt) was studied by growing plants in four light environments [out-of-doors in full sun and under 50% shade, and in a growth chamber at 800 μE m2 sec-1 photosynthetically active radiation, 400 to 700 nm (PAR) and 150 μE m-2 sec-1 PAR], and then determining, with an infrared gas analyzer (IRGA), the photosynthetic rates of single leaves exposed to a range of light intensities from 100 to 2000 μE m2 sec-1 PAR. The plants grown in high light had higher photosynthetic rates throughout the range of 100 to 2000 μE M-2 sec-1 PAR. Maximum photosynthetic rates were 37 mg CO2 dm-2 h-1 for plants grown in full sun out-of-doors and 16.5 mg CO2 dm-2 h-1 for plants grown in low light in the growth chamber. There was no indication of positive adaptation to low light intensity in Sakhalin knotweed. Differences in light-saturated photosynthetic rates were closely related to differences in mesophyll conductance and chlorophyll content per unit leaf area.

Nutrient-solution-grown pepper (Capsicum frutescens L. ‘Early Calwonder’) absorbed 62% of the diphenamid (N,N-dimethyl-2-2-diphenylacetamide) supplied via the roots for 48 h, and 74% in 150 h. Extensive translocation accompanied absorption, and 70 ± 3% of the absorbed 14C was present in shoots of plants harvested after 24- to 150-h treatments. Diphenamid was metabolized rapidly to chloroform-soluble and water-soluble compounds, and to unextracted residues. Chloroform-soluble compounds persisted for 150 h and accounted for more than 50% of the 14C in leaves. Water-soluble compounds other than N-hydroxymethyl-β-D-glycosides accounted for 25% of the water-soluble metabolites in leaves of nonfumigated plants. Ozone fumigation did not affect diphenamid absorption or translocation significantly. In leaves, ozone-enhanced accumulation of water-soluble metabolites more polar than N-hydroxymethyl-N-methyl-2,2-diphenylacetamide-β-D-glucoside (MDAG) and unextracted residues was observed. Ozone fumigation reduced the accumulation of these 14C-fractions in roots.

Metabolites of diphenamid (N,N-dimethyl-2,2-diphenyl-acetamide) were purified from extracts of pepper plants (Capsicum frutescens L. ‘Early Calwonder’) treated via nutrient solution with the herbicide or several of its analogs. The major metabolites were characterized. Diphenamid was metabolized partially via a previously unreported pathway to N,N-dimethyl-2-phenyl-2-[(hydroxyphenyl)-β-0-D-glucosyl] acetamide and its monomethyl analog, and to N-hydroxymethyl glycosides previously reported in other species. Ozone fumigation stimulated the production of both types of glycoside-conjugates. Leaves of plants that had been treated with 30 μM diphenamid and fumigated with ozone for 146 to 149 h contained 304 and 560 nmoles per gram of fresh weight of the hydroxyphenyl and N-hydroxymethyl conjugates, respectively.

We have come together to discuss the way in which weeds and water work together to influence yields in agriculture. In the small allotment of time available to us this morning a review of basic knowledge about this relationship would be so general that it could help no one. I believe it would be more appropriate, and more helpful for a group so large, if I tell you of some of the hard realities which come to bear on food production across the world because of this relationship of weeds with moisture. These stories will have to do with such practical matters as the expansion of the world's most important crop, and the difference between good and bad crops on the two sides of the same river under identical climatic conditions in Middle Asia.

Putting green turf containing perennial ryegrass (Lolium perenne L. ‘Medalist IV’) overseeded on a bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’] was treated with single and sequential herbicide treatments during the spring and transition period from cool to warm season grass. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] at 2.2 or 4.4 kg/ha and butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] at 3.4 or 6.7 kg/ha reduced the quality of putting green turf immediately after treatment in early spring. Turf injury was greater with oxadiazon than with butralin. Two applications of MSMA (monosodium methanearsonate) at 2.2 or 3.4 kg/ha resulted in a lower quality turf with less ryegrass when compared with the untreated check. Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] at 1.1 kg/ha severely injured ryegrass and resulted in a lower turf quality.

Rhizomes of quackgrass [Agropyron repens (L.) Beauv.] and johnsongrass [Sorghum halepense (L.) Pers.] were buried at various depths in the soil in the fall of 1972 and 1973, then removed at different times for viability tests. Quackgrass rhizomes retained viability at 2 cm where the coldest temperatures were −17 C. Johnsongrass rhizomes survived the winter at depths of 20 cm or more, and were killed at temperatures below about −9 C. Quackgrass rhizomes had a higher concentration of lipids and higher proportions of unsaturated fatty acids than did johnsongrass rhizomes. This difference may contribute to the superior cold tolerance of the quackgrass rhizomes.

The use of electrolytic conductivity as a measure of cell membrane disruption was tested on buckwheat (Fagopyrum esculentum Moench. cv. ‘Tokyo’) plants which had been sprayed with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. All treatments which resulted in tissue damage caused significant increases to the solutions where the discs were floated for measurement. The highest conductivity measurement (most membrane disruption) was obtained from paraquat. The highest concentration for each herbicide gave higher conductivity measurements than lower concentrations. A difference in the pattern of conductivity change induced by the two chemicals implies a different mode of action for each.

The tolerance of wheat (Triticum aestivum L. ‘Waldron’) and wild oat (Avena fatua L.) to various rates of flufenprop-methyl {methyl-2-[benzoyl(3-chloro-4-fluorophenyl)amino]propanoate} applied weekly after wheat and wild oat emergence was determined under field conditions. Wild oat control increased at all growth stages as flufenprop-methyl rate increased. Wild oat control was greater than 80% with flufenprop-methyl at all rates when applied up to 6 weeks after wild oat emergence: (anthesis stage), but decreased when application was delayed further. Wheat was most susceptible to flufenprop-methyl during anthesis. Flufenprop-methyl at 0.56 kg/ha injured weed-free wheat only at the boot and anthesis stages. Injury intensity and the number of weeks that injury remained evident increased as flufenprop-methyl rate increased. Flufenprop-methyl injury to wheat was expressed as reduced plant height, grain yield, and kernels per spike and increased grain protein. Plant height reductions were attributed to reduced cell elongation. Grain yield reductions resulted from reduced kernels per spike.

Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl]amino] phenyl] acetamide} at concentrations of 2.9 × 10-4 M and above retarded the growth of corn (Zea mays L. ‘Pioneer 3369A’) grown in nutrient culture. Dwarfing was accompanied by some plant distortion and chlorosis of the bases of those leaves formed soon after treatment. The chlorosis was associated with decreased chlorophyll a content. Chlorophyll b content was not affected. The growth-retardant effects of mefluidide could not be reversed by applications of gibberellic acid. Using cucumber (Cucumis sativus L. ‘Ashley’) cotyledon discs, a low level of mefluidide (2.9 × 10-5 M) increased the incorporation of 14C from leucine into protein, while a high concentration (2.9 × 10-4 M) reduced incorporation. Neither concentration affected the absorption of 14C-leucine.

The influence of calcium arsenate (48% w/w tricalcium arsenate) rate, physical form, time of application, and phosphorus (P) rate on the growth of annual bluegrass (Poa annua L.) and Bray P1 extractable arsenic (As) were investigated. Both powder and granular formulations reduced clipping yields and enhanced extractable As levels. Higher initial soil As activity and significantly better control were obtained in one study when the powder formulation was used. Similar levels of control were achieved whether the As was applied prior to germination or to the mature turf. Soil P-levels did not influence the effectiveness of either As formulation.

Specially designed growth boxes were used to simulate field subsurface injection of phenoxy herbicides. Sorghum (Sorghum vulgare Pers.) seedlings were grown in stainless steel containers (inserts) which were placed in plexiglass boxes containing a soil layer that had received 2,240 kg/ha of a 50:50 mixture of the n-butyl esters of 2,4-D [(2,4-dichlorophenoxy)-acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)-acetic acid]. Plant height data were collected periodically for all treatments. Subsurface herbicide application to both intact and cut root systems significantly altered root growth. Plants with treated, intact root systems showed retarded growth which became more pronounced with time. Plants whose root systems were treated, and cut on day 22, showed an initial acceleration of growth; a trend which eventually reversed itself and resulted in control plant height exceeding that of treated plants.