At least two weedings within the first 5 weeks after sowing are necessary to minimize yield reduction caused by weeds in cowpea [Vigna unguiculata (L.) Walp.]. During a 3-yr study, a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.0 to 3.0 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 10.0 kg/ha, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at 2.0 or 2.5 kg/ha controlled most annual grasses effectively. Itchgrass (Rottboellia exaltata L.) was controlled with pendimethalin at 2.5 kg/ha, but metolachlor had no effect on this weed. These herbicides caused no crop injury and cowpea grain yield was as good as in the handweeded and weed-free plots. Alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl) acetanilide] applied preemergence at 2.0 kg/ha was effective against annual weeds, but was phytotoxic to cowpea.

Birdsfoot trefoil (Lotus corniculatus L.) was direct-seeded into five different grass sods after treatment with dalapon (2,2-dichloropropionic acid), glyphosate [N-(phosphonomethyl)glycine], or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at varying rates for vegetation control. During establishment, the stands of birdsfoot trefoil were acceptable in all treated- and untreated-sod grass sods except 1 yr in untreated tall fescue (Festuca arundinacea Schreb.) and timothy (Phleum pratensis L.) and 1 yr in tall fescue receiving 3 kg/ha of dalapon. Herbicide treatments resulted in a more rapid development of a significant legume component in the sward and an increase in forage yield over the untreated plots. Minimum herbicide application rates for best return for grass sod control were 0.5, 1, and 5 kg/ha respectively for paraquat, glyphosate, and dalapon.

Corn (Zea mays L.) in soybeans [Glycine max (L.) Merr.] currently can be controlled with either glyphosate [N-(phosphonomethyl)glycine] applied to corn that is taller than soybeans, or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} sprayed over-the-top of both corn and soybeans. We found a wide range in tolerance to over-the-top spray applications of glyphosate among 240 F2 hybrids of corn. Glyphosate was then applied with a rope-wick to one tolerant and one susceptible F2 corn hybrid growing in soybeans. In only two instances out of six (three stages of growth times 2 yr), the susceptible corn was controlled better than the tolerant corn; but, in these two instances, the better control was not reflected in greater soybean yields. In another experiment, one F2 corn hybrid identified (in a previous study) as tolerant of diclofop and one identified as susceptible were sprayed in soybeans with over-the-top diclofop treatments. In 11 instances out of 12 (two stages of growth times three rates times 2 yr), the susceptible corn was controlled better than the tolerant corn, and in nine of these instances, the better control was reflected in greater soybean yields. Corn parentage could be important in determining the degree of control obtained with either herbicide, but this is more likely with diclofop than with glyphosate.

Response of wild oat (Avena fatua L.) at the three-leaf stage to five postemergence herbicides, asulam (methyl sulfanilylcarbamate), barban (4-chloro-2-butynyl m-chlorocarbanilate), diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, difenzoquat (1,2-dimethyl-3,5-diphenyl-1 H-pyrazolium), and flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] was measured and compared in nine physiological and biochemical processes (chlorophyll content, photosynthesis, photosynthate translocation, and changes in ATP, lipids, DNA, RNA, amino acids, and proteins). Content of chlorophyll a and b was reduced by the application of diclofop and difenzoquat. Photosynthesis was inhibited with all five herbicides, but photosynthate translocation from the leaves to the roots was reduced only with diclofop, difenzoquat, and flamprop. ATP production was inhibited by all herbicides except flamprop, which increased the ATP content. Incorporation of 32P into lipids was reduced by all herbicides except asulam. The incorporation of 32P into nucleic acids (DNA and RNA) was inhibited by all five herbicides. Serine and threonine, especially the latter, accumulated in large quantity with all herbicides except difenzoquat. Protein content (water-soluble,-insoluble, and total amount) was reduced by asulam, diclofop, and flamprop, but barban and difenzoquat reduced water-insoluble and total proteins only. Apparently, all herbicides examined affected more than one physiological function and biochemical process in wild oat.

Field and greenhouse trials have shown that ultra-low-volume applications (ULV) of glyphosate (N-(phosphonomethyl)glycine] exhibit a greater phytotoxic effect on barley (Hordeum vulgare L. ‘Bonanza′) at a given rate than do high-diluent-volume applications with a conventional hydraulic sprayer. Three greenhouse studies and one field trial were conducted to evaluate the influence of individual drop makeup on the effectiveness of ULV applications. Barley plants were treated at the four-leaf stage with one, three, or nine drops (1 μl each) of glyphosate and a non-ionic surfactant with the concentration of the drops adjusted so that the total amount of active ingredient applied to each plant was constant. Application of a single, concentrated drop was significantly more effective in reducing total shoot growth than were applications of more dilute drops in greater number. When the dilute drop was supplemented with additional surfactant, phytotoxicity was restored, provided there was a sufficiently high concentration of glyphosate in the drop. With the substitution of a commercial formulation of glyphosate, the response of barley to variations in drop number and drop concentrations followed a similar trend. The response of field-grown plants did not differ from plants grown under controlled conditions.

Seed production was studied near Lincoln, Nebraska for musk or nodding thistle (common names used for large-flowered species of Carduus – C. macrocephalus Desf., C. nutans L., C. thoermeri Weinm.). Four levels of seed maturity were studied from separate groups of plants with the heads harvested at the full-bloom stage, 2 days after full bloom, 4 days after full bloom, and at full maturity. The first heads to bloom (terminal) averaged about 1000 seeds/head and the last to bloom (lateral branches near the base of the plant), ca. 125. Plants produced only 26 good quality seeds/plant when the heads were all clipped at the full-bloom stage, but the plants with heads allowed to go to maturity produced 3580 of the good quality seeds/plant. Plants with heads clipped at 2 and 4 days after full bloom produced 72 and 774 good quality seeds, respectively.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 6.7 kg/ha, twice the recommended rate, stunted early-season growth of ‘Jubilee,’ ‘Commander,’ and 'Stylepak’ sweetcorn (Zea mays L.) 9 to 15%, reduced plant populations of Commander and Stylepak 12 to 15%, reduced the kernel yield of Jubilee and Stylepak 14 to 16%, and delayed ripening of Jubilee and Stylepak by 2 or 3 days. Alachlor at 3.4 kg/ha slowed early-season growth of Jubilee and Stylepak, but reduced yield and delayed ripening of only Jubilee. EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloracetamide) and vernolate (S-propyl dipropylthiocarbamate) + R-25788 at 4.5 + 0.4 or 9.0 + 0.8 kg/ha did not reduce the growth, yield, or quality of the three sweetcorn cultivars. Planting date did not influence the response of sweetcorn to the herbicides. In these experiments, none of these herbicides injured sweetcorn severely, as has sometimes occurred in commercial fields.

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] at 2.2 to 4.4 kg/ha controlled goosegrass [Eleusine indica (L.) Gaertn.] without injuring bermudagrass [Cynodon dactylon (L.) Pers.], but severely injured overseeded common ryegrass (Lolium multiflorum Lam. common) and perennial ryegrass (Lolium perenne L. ‘Medalist VI′) for a 5 – to 6-week period after treatment in the spring and thus reduced turf quality. The transition was poor because ryegrass was killed faster than bermudagrass could initiate new spring growth. The combination of bensulide [O, O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] and oxadiazon applied as a single treatment at 6.7 + 1.7 kg/ha controlled goosegrass as effectively as did oxadiazon applied alone at 2.2 kg/ha or higher rates and did not injure the turf, so the transition from cool-season grass to bermudagrass was uniform. Aeration of an overseeded bermudagrass turf after applications of oxadiazon did not significantly decrease goosegrass control.

The persistence of hormone-type herbicides in tissues of susceptible crop plants was studied under growth-chamber and field conditions. The susceptible plants selected were tomatoes (Lycopersicon esculentum Mill.), soybeans [Glycine max (L.) Merr.], and turnips (Brassica rapa L.). Foliage of each species was exposed to herbicides at levels that represented spray drift situations, and the decline of residues was investigated through subsequent chemical analysis. The disappearance of 2,4-D [(2,4-dichlorophenoxy)-acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], mecoprop {2-[(4-chloro-o-tolyl)oxy]propionic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and dicamba (3,6-dichloro-o-anisic acid) was almost linear when concentration data were plotted against the logarithm of time. The results indicate that for practical purposes a kinetic rate equation [conc. = a – b log (time)] would describe the residue decline.

The people of the world required from the dawn of time until 1830 to reach a population of 1 billion. By 1960, we reached 3 billion and by 1980 we had a population of about 4 billion. It is estimated that by the year 2000 there will be 7 billion people in the world. Just 30 yr from now the world's population will have doubled. This means that within the next 30 yr we must produce as much food as we have produced since the beginning of history. Can we feed this many people? Yes, but expanded research to develop improved technology will be required to meet the challenge.

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%).

We compared diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, as an early over-the-top spray treatment, and glyphosate [N-(phosphonomethyl)glycine], applied twice in repeated applications with a rope-wick applicator, for control of simulated volunteer corn (Zea mays L.) planted in clumps at various intervals in rows of soybeans [Glycine max (L.) Merr.]. Uncontrolled corn at the lowest density (clumps 2.4m apart in the row) reduced soybean yields an average of 31%. Both herbicides were highly effective in controlling corn, but when corn densities were high, diclofop treatments often resulted in greater soybean yields than did glyphosate treatments — presumably because corn interfered with the soybeans for a longer time before glyphosate was applied.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] toxicity, absorption, translocation, and metabolism were investigated in corn (Zea mays L.) and yellow nutsedge (Cyperus esculentus L.). Metolachlor did not inhibit seed germination in corn or tuber germination in yellow nutsedge. It did not kill yellow nutsedge tubers that were exposed to 4 ppmw for 9 weeks. Metolachlor (10 ppmw) applied in soil above the seed significantly reduced corn shoot growth, but the same concentration around or below the seed had no effect. A soil mixture with metolachlor (1 ppmw) placed above or around yellow nutsedge tubers significantly reduced shoot growth, but placement around the tuber was the most toxic; placement below the tuber had no effect on shoot growth. The concentration of metolachlor that resulted in 50% reduction of shoot growth of 4-day-old seedlings in solution culture was > 10−4 M for corn and <10−6M for yellow nutsedge. Root-applied 14C-metolachlor was acropetally translocated to shoots of both species following a 7- to 13-day absorption period, with yellow nutsedge translocating the highest portion of the absorbed material to shoots. In 2-day-old seedlings with roots exposed to 14C-metolachlor for up to 48 h, both species absorbed and translocated the radioactivity to shoots, but corn absorbed much more than yellow nutsedge. When the 14C-metolachlor was applied to shoots of both species, the radioactivity was translocated basipetally into roots. Yellow nutsedge exuded appreciable 14C-metolachlor out of the roots and absorbed more 14C-metolachlor through shoot tissues than corn. Both corn and yellow nutsedge seedlings readily converted the 14C-metolachlor to metabolites, but corn was able to metabolize the 14C-metolachlor at a faster rate than yellow nutsedge and also produced more metabolites.

Burs of common cocklebur (Xanthium strumarium L.) obtained from Stoneville, Mississippi; Urbana, Illinois; and Lamberton, Minnesota, were used in greenhouse and growth chamber studies. The Mississippi and the Illinois strains were both classified as being in the “strumarium” complex of X. strumarium, whereas, the Minnesota strain was classified as being in the “hybrid” complex. The Minnesota common cocklebur developed branch leaves in the leaf axils of the main stem to a much greater extent than did the Mississippi and Illinois common cocklebur. The Mississippi common cocklebur was frequently more tolerant of postemergence applications of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] than were the Illinois and Minnesota common cockebur. The Mississippi and Illinois common cocklebur developed leaf necrosis when sprayed with an insecticide formulation containing malathion (o, o-dimethyl phosphorodithioate of mercaptosuccinate) and petroleum solvents; the Minnesota common cocklebur did not.

Three musk thistle (Carduus thoermeri Weinm.) sites that were infested with a weevil (Rhinocyllus conicus Froel.) and a fourth non-infested site were evaluated for numbers of insects and seeds per seed head. At four successive weekly intervals, seed heads were sampled just after flowering. Initial sampling was in 1978 and was repeated in 1979. Weevil incidence in heads blooming during the first week was 6.7/head in 1978 and 28.0 in 1979. At infested sites, production of fully developed seeds averaged 28% less than at the non-infested site in 1978 and 78% less in 1979. Heads that were in bloom during the fourth sampling week had an infestation rate less than one weevil/head in both years. Fully developed seeds germinated well (96 to 99%) and were not affected by date of bloom. Because many heads bloomed during the third and fourth weeks, a large number of viable seeds were still produced at infested sites.

Greenhouse benches and pots were specially designed to facilitate herbicide research on plants. Four 0.8-cm risers were added to the bottom of polyethylene pots to improve drainage after subirrigation or surface watering. A rule die was made to punch out paper discs needed to cover the holes in the bottom of the pots to prevent soil loss during watering or drainage. Flat, level greenhouse tables with a 3-cm hinged side around the edges, were covered with 2-mm polyethylene sheeting to facilitate water retention when the side was in the up position during subirrigation and subsequent drainage of water when the side was down. Much time was saved and the soil was watered more uniformly by this system. Economics dictated discarding pots after herbicide experiments rather than incurring the expense of washing them and risking contamination of subsequent experiments.

Three cultivars of wild rice (Zizania palustris L.) were grown with various densities of common waterplantain (Alisma triviale Pursh) established from seeds and from rootstocks during 1979 and 1980. Wild rice cultivars did not differ in their response to common waterplantain interference. Common waterplantain grown from seeds at densities up to 82/m2 did not significantly reduce wild rice yield. Common waterplantain established from rootstocks significantly reduced wild rice yield at densities as low as 3/m2. A density of 43/m2 reduced wild rice yield by 91%. The yield component most susceptible to interference from common waterplantain was panicles per plant. The number of seeds per panicle was reduced by densities as low as 11/m2 and seed weight was reduced by densities of 22/m2 or greater. Only a density of 43/m2 reduced the stand of wild rice. Common waterplantain established from rootstocks at a density of 17 plants/m2 did not reduce wild rice yield if removed by 7 weeks after planting. Interference from common waterplantain for 9 weeks or longer reduced wild rice yield by approximately 50%.

The influence of herbicide formulation and time of herbicide application on smutgrass [Sporobolus poiretii (Roem. & Schult.) Hitchc.] control and phytotoxicity to the major perennial forage-grass species were determined. Dalapon (2,2-dichloropropionic acid) applied at rates of 4.8 kg/ha and higher gave excellent control regardless of time of application. However, 4.8 kg/ha dalapon applied to Pensacola bahiagrass (Paspalum notátum Flügg ‘Pensacola′) and bermudagrass [Cynodon dactylon (L.) Pers.] in the spring, and to tall fescue (Festuca arundinacea Schreb. ‘Ky 31′) in the fall and spring, was phytotoxic. Applications of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} 80W (80% wettable powder) formulation at 2.4 kg/ha, or fertilizer coated with tebuthiuron at 2.4 kg/ha, gave excellent smutgrass control. The pelleted formulation of tebuthiuron was less phytotoxic to the forage species than the other formulations.

In a special symposium on weed biology presented at the 1975 annual meeting of the Weed Science Society of America, Parka (37) reviewed the trend of published papers in WEED SCIENCE related to weed biology over the 20-yr period, 1952 to 1972. His data indicated a steady increase from 9.2 to 17.2% of published papers directly related to weed growth and development. My recent assessment of similarly classified papers in 1978, 1979, and 1980 showed a remarkable increase to 21.9, 24.3, and 27.2%, respectively. Further, the more recent papers on weed growth and development also include crop-effect data, i.e., the association of weed growth with crop competition.