Glyphosate [N-(phosphonomethyl)glycine] consistently controls many winter annual weeds in dormant bermudagrass [Cynodon dactylon (L.) Pers.] but injures actively growing turf. Experiments were conducted to determine the effects of dates of glyphosate treatments on control of winter annuals in different stages of maturity and on the tolerance of bermudagrass when applied to the turf at different stages of greenness from dormant turf in the winter to actively growing turf in the spring. Glyphosate was applied at rates of 0, 0.3, 0.6, 1.1, and 2.2 kg/ha to different plots of winter annuals and bermudagrass at 3-week intervals from February 13 to May 3. Glyphosate at 0.3 kg/ha controlled at least 90% of annual bluegrass (Poa annua L.), spur weed (Soliva sessilis P. & K.), and corn speedwell (Veronica arvensis L.) within a 6-week period regardless of the date of treatment. All glyphosate treatments injured bermudagrass when applied to semi-dormant or actively growing turf. Bermudagrass treated with glyphosate at 0.3 kg/ha was injured the least and the turf had essentially recovered by 6 weeks after treatment. However, the injury from higher rates (0.6 to 2.2 kg/ha) was too severe to be acceptable in turf areas. Glyphosate did not severely injure bermudagrass when applied to dormant turf.

Tobacco (Nicotiana tabacum L. ‘X-73’) callus tissue cultures were used in a bioassay system for determining the effect of the following substituted 2,6-dinitroaniline herbicides on growth: trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine); oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide); benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine); AC 92390 (N-sec-butyl-2,6-dinitro-3,4-xylidine); penoxalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine]; GS-38946 (N-ethyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline); chlornidine [N,N-di(2-chloroethyl)-4-methyl-2,6-dinitroaniline]; nitralin [4-(methylsulfonyl)2,6-dinitro-N,N-dipropylaniline]; dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine); isopropalin (2,6-dinitro-N,N-dipropylcumidine), and profluralin [N(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine]. The molar concentration required to inhibit fresh weight gain by 50% (I50) was determined by using linear regression analysis on data from a range of five concentrations of each chemical. I50 values did not correlate with structural variations or available physical constants. Herbicides listed in order of increasing activity are AC 92390< GD-38946<profluralin = isopropalin<benefin = chlornidine = trifluralin = nitralin<oryzalin = penoxalin < dinitramine. Exogenously applied D-α-tocopherol acetate at 100 times the I50 concentrations decreased the inhibition of tissue growth by the herbicides.

A simple technique is described for rapid determination of weed seed, rhizome, corm, or bulb populations in soil. Soil samples were placed in nylon mesh bags. The soil was washed from the bags by machine leaving only a small residue including the desired propagules. These were hand separated and the soil population of a given plant species calculated. The total manipulation time per sample was approximately 10 min.

Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] and tetrafluron {N,N-dimethyl-N′-[3-(1,1,2,2-tetrafluoroethoxy) phenyl] urea} are two urea-type herbicides for weed control in cotton (Gossypium hirsutum L.). In some years, because of cotton stand failure, an alternate crop must be established. Soybeans [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] are possible alternate crops if they can withstand the residues left from herbicides used for weed control in cotton. Soybeans and grain sorghum were planted 3, 6 and 9 weeks after fluometuron and tetrafluron applications to soil at Knoxville and Milan, Tennessee, in 1975 and 1976. Tetrafluron residues were more toxic to grain sorghum and soybeans than were fluometuron residues. Grain sorghum was less susceptible than soybeans to both herbicides. Grain sorghum was planted 3 weeks after fluometuron (1.7 kg/ha) and tetrafluron (1.7 kg/ha) applications without severe yield reduction. Soybeans were planted in non-treated soil between banded tetrafluron (1.7 kg/ha on a treated area basis), 3 weeks after herbicide application, without significant yield reduction; but when a seedbed was prepared, a 9-week waiting period was required. When soybeans were planted into soil receiving a broadcast application of tetrafluron (1.7 kg/ha), a 9-week waiting period was not sufficient to reduce the residues to a non-toxic level. Soybeans planted 6 and 9 weeks following a broadcast application of fluometuron may or may not sustain yield reduction depending on rainfall frequency and intensity and soil type.

The effects of 8-, 12-, and 16-h photoperiods on the growth and reproductive biology of purple nutsedge (Cyperus rotundus L.) were investigated over a 3-month period. Plants under the 8-h photoperiod produced the least total, shoot, root, rhizome, and tuber dry weight. Flowering occurred only at the 12-h photoperiod; thus, purple nutsedge is intermediate in flowering response to daylength. Although the total dry weight varied with photoperiod, the relative amount of dry weight (as percent of total weight) partitioned to shoots, roots, rhizomes, and tubers was constant.

2,4-D [(2,4-dichlorophenoxy)acetie acid] and dalapon (2,2-dichloropropionic acid) were applied to a natural stand of annual weeds at a time near flowering to determine effects on seed production and the dormancy and viability of seeds produced. At rates of 0.6 and 1.1 kg/ha, 2,4-D reduced, respectively the seed production of common lambsquarters (Chenopodium album L.) 99 and 99%, redroot pigweed (Amaranthus retroflexus L.) 77 and 84%, and jimsonweed (Datura stramonium L.) 64 and 100%, while giant foxtail (Setaria faberi Herrm) seed production was increased to 307 and 381% of the control, respectively. Dalapon at rates of 2.2 and 4.5 kg/ha reduced respectively seed production of giant foxtail 100 and 100%, and jimsonweed 100 and 91%. Before and after overwinter burial in the soil, common lambsquarters seeds from plants treated with 4.5 kg/ha dalapon were less dormant than control seeds. After overwintering, redroot pigweed seeds from dalapon-treated plants were less dormant than controls, and more seeds survived the winter burial. Common lambsquarters and redroot pigweed seeds from plants treated with 1.1 kg/ha 2,4-D were more dormant than control seeds before overwintering,’ while giant foxtail seeds from 2,4-D treated plants were less dormant than controls after overwintering. Viability of seeds produced by herbicide-treated plants, as determined by germination in KCN, was not greatly different from control seeds. Treatment with 2,4-D or dalapon resulted in the production of common lambsquarters seeds which produced seedlings about half as vigorous as controls. Jimsonweed seedlings grown from seeds from 2,4-D-treated plants showed phenoxy herbicide injury symptoms.

Yellow foxtail [Setaria glauca (L.) Beauv.], giant foxtail (Setaria faberi Herrm.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], robust white foxtail (Setaria viridis var. robusta-alba Schreiber), and robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber) were grown from seed in pure stands in sand-soil nutrient solution cultures at various nitrogen levels. Within taxa dry weight of herbage differed significantly with nitrogen level, but dry weight of roots did not. Yellow foxtail produced more leaf area than the other four taxa regardless of nitrogen level. At the low nitrogen level, yellow foxtail produced significantly more root mass (dry weight) than the other taxa; giant foxtail was second in root-mass production. The order of root-mass production was the same at medium and high nitrogen levels, but only at a 12-h photoperiod. At a 16-h photoperiod, root production was equal in yellow foxtail and giant foxtail and was significantly greater in these taxa than in giant green foxtail, robust white foxtail, or robust purple foxtail. Generally similar relationships were evident in the root: shoot ratios. The chances for survival with giant foxtail taxa should be better for yellow foxtail than for the other foxtail taxa since yellow foxtail produced more root mass even at low nitrogen fertility, a condition common in undistrubed sites such as roadsides and fencerows.

For effective biological control through augmentation, Bactra verutana Zeller, would have to be released against purple nutsedge (Cyperus rotundus L.) in May and June when temperatures are cooler than they are from late July through September when maximal natural populations of this biological control agent occur. Bactra larvae exposed to simulated mid-May (24/13 C) and mid-June (29/18 C) temperature regimes developed more slowly than larvae exposed to the mid-July (32/26 C) temperature regime, but nutsedge plant growth was also slower. Thus, the relative amounts of feeding injury were similar at all three regimes. Larval feeding generally increased the number of shoots slightly, but not significantly, reduced significantly the production of inflorescences, and reduced the weight of total dry matter produced between 28 and 49%.

A small enclosure was developed for isolating areas of submersed weeds within bodies of open water and for evaluating the efficacy of herbicides. The enclosure can be easily dismantled and transported between lakes and can be moved readily by flotation as a unit within a lake. Its use will permit smaller research plots, less herbicide per treatment, more plots within a uniform environment, and more accurate assessment of the relationship between herbicide concentration and length of exposure than are possible with the more commonly used techniques.

The effects of Pennsylvania smartweed (Polygonum pensylvanicum L.) interference in soybeans [Glycine max (L.) Merr. ‘Pickett 71’] were studied in the field under a naturally occurring weed population. Soybean seed yield was reduced an average of 13% by a density of eight Pennsylvania smartweed plants per 10 m of row. Greater yield reductions of 21, 37, and 62% resulted from full-season interference by densities of 16, 32, and 240 weeds per 10 m of row, respectively. Fewer than five weeds per 10 m of row did not significantly reduce crop yield. A natural population of 240 weeds per 10 m of row did not reduce soybean yield if the period of interference was limited to 6 weeks or less after crop emergence. However, more than 6 weeks of weed interference resulted in significant yield reduction. Conversely, if the crop was kept weed-free for a period of 4 weeks or more after emergence, seed yield was not reduced. No allelopathic interaction between the two species was observed in greenhouse studies using a recirculating nutrient solution and alternate pots of soybeans and Pennsylvania smartweed.

Before I try to paint a broad canvas as a background to this evening's discussion I think we should be clear what we mean by ‘discipline of weed science’. The word ‘discipline’ according to the Oxford English Dictionary means ‘a department of knowledge’ or ‘the art of war’. This latter 15th Century definition might seem appropriate to our struggle against weeds! What, though, is meant by ‘weed science’?

Experiments were conducted in controlled environmental chambers to determine the influence of temperature on the phytotoxicity of seven soil-applied herbicides. Diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} soil incorporated or surface applied, was more toxic to wild oat (Avena fatua L.) shoots at 10 and 17 C than at 24 C. Efficacy of diclofop was enhanced with soil incorporation. Diclofop toxicity to wild oat roots was not influenced by a change in temperature. EPTC (S-ethyl dipropylthiocarbamate) stimulated sugarbeet (Beta vulgaris L. ‘American Crystal Hybrid B’) shoot dry weight production at 10 C and caused dry weight reduction at 24 C. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] toxicity to barley (Hordeum vulgare L. ‘Larker’) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] toxicity to oats (Avena sativa L. ‘Chief’) increased with increased temperature from 10 to 17 C. Temperatures within the range of 10 to 24 C did not affect trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) toxicity to barley or BAY-5653 [N-(2-benzothiazolyl)-N-methylurea] or chloamben (3-amino-2,5-dichlorobenzoic acid) toxicity to oats.

Postemergence difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) for wild oat (Avena fatua L.) control in spring wheat (Triticum aestivum L.), durum wheat (Triticum durum Desf.), and barley (Hordeum vulgare L.) was evaluated in the field, greenhouse, and controlled environmental chamber. Wild oat control with difenzoquat was greater at the five- that at the three and one-half or two-leaf stages of growth. Barley tolerance to difenzoquat was excellent; however, spring wheat tolerance was influenced by cultivar. Durum wheat generally was more tolerant of difenzoquat than spring wheat. Tank mix combinations of broadleaf herbicides with difenzoquat had no effect on crop injury or wild oat control. Wild oat control with difenzoquat was greatest with adequate soil moisture, adequate fertility, warm air temperatures and high relative humidity. A simulated rainfall of 0.25 mm within ½ h or 1 mm within 4 h of application reduced wild oat control with difenzoquat.

Germination of common mullein (Verbascum thapsus L.) in relation to constant and alternating temperatures, and light quality and duration was studied. In the dark, optimum germination occurred with 8-h warm periods of 30 to 40 C alternating with 16-h cold periods of 15 to 35 C. In the dark, no germination occurred below 10 C. With light during the 8-h warm periods, germination occurred at temperatures from 2 to 40 C, alternating with 0 C cold periods. The range of optimum temperatures for germination was also greatly expanded with light. Exposures to 24-h periods of red light, followed by incubation in the dark, produced the same germination response as 8 h of white light daily. Common mullein seeds germinated on the surface of the soil even though the seeds did not have mucilage.

No differences in the anatomy or bud pattern development were observed between young tap and lateral roots of rush skeletonweed (Chondrilla juncea L.). Shoots and lateral roots arise from meristemic zones that originate from a continuous pericyclic ring. Incubation of excised root segments resulted in rapid development of stem buds which showed geotropic response in 24 h. The development of identifiable leaf initials occurred prior to emergence through the epidermis in 8 days.

Nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] are 2 diphenylether herbicides which are phytoactive on common purslane (Portulaca oleracea L.). The stomata of common purslane are normally open during the day and closed at night. Nitrofen and oxyfluorfen applications to common purslane leaves cause the stomata to close which is a result of increased membrane permeability. A slight increase (0.6 C) in leaf temperature and a decrease (2 bars) in the apparent water potential was evident after 6 h. Membrane degradation caused some cells to collapse and caused the leaves to appear pitted. Ethylene synthesis was stimulated (0.9 ppmv) causing a loss of plastids from the bundle sheath cells and finally leaf abscission, 8 to 24 h after treatment.

Dinoseb (2-sec-butyl-4,6-dinitrophenol) and certain dinitroaniline herbicides suppressed root rot caused by Aphanomyces euteiches Drechs. and other fungal pathogens in peas (Pisum sativum L.). Dinoseb was the most effective. At 6.72 kg/ha pre-plant incorporated (PPI) it reduced the disease severity index (DSI) in glasshouse bioassays to the level considered safe for general use by commercial growers. In fields tests disease severity was reduced and yield of peas was increased with dinoseb. Dinitroaniline herbicides reduced DSI values to the level considered safe for early crop peas. A simplified DSI method of measuring root rot based on mid-season root symptoms was found to be effective. Weed control was superior with the dinitroanilines and propachlor (2-chloro-N-isoproylacetanilide). Dinoseb significantly reduced weed populations relative to untreated plots. Several dinitroaniline treatments caused stunting and stand reduction.

Application of 112 to 336 kg/ha N as ammonium nitrate [NH4(NO−3)] failed to affect population numbers of common lambsquarters (Chenopodium album L.), giant foxtail (Setaria faberi Herrm.), velvetleaf (Abutilon theophrasti Medic.), jimsonweed (Datura stramonium L.), or redroot pigweed (Amaranthus retroflexus L.). Common lambsquarters seeds harvested from NO−3-treated plots were less dormant than control seeds. Seed germination in the laboratory increased from 3.0% for control seeds to 34.0% for seeds harvested from plots treated with 280 kg/ha N as NH4(NO−3). Nitrate concentration in common lambsquarters seeds increased as nitrogen fertilization increased. Seeds from nonfertilized plots contained 18.7 μg/g NO−3, while seeds from plots fertilized with 280 kg/ha N contained 126.3 μg/g. Adding exogenous NO−3 to the germination medium brought the germination of most seed lots to a similar level, except for control seeds which germinated at a lower rate. In contrast to common lambsquarters, nitrogen fertilization did not greatly affect dormancy or NO−3 accumulation in velvetleaf seeds. Exogenous NO−3 failed to stimulate velvetleaf germination because dormant velvetleaf seeds did not imbibe.

The potential losses from spray applications of glyphosate [N-(phosphonomethyl)glycine] with and without the inclusion of a polymer thickening agent were evaluated in field tests, applied under identified weather conditions with a boom-nozzle ground sprayer, helicopter, and fixed-wing aircraft. The downwind transport and diffusion of the spray loss was assessed by means of Mylar fallout sheets, high volume air samplers, and 4-leaf wheat (Triticum aestivum L. ‘Anza’) plants. Lowest drift losses occurred, under 0.01 g/ha on fallout sheets at 100 m, with deflector fan nozzles (KGF) operating at a low pressure (7 kPa) on the ground sprayer. Drift losses from a helicopter equipped with micro-jet nozzles were only slightly higher, less than 0.03 g/ha on fallout sheets at 100 m. Drift losses from 8003 nozzles mounted on a ground sprayer and D-6 jet nozzles directed back on fixed wing aircraft produced much higher drift deposits, from 0.2 to 1.0 g/ha on fallout sheets at 100 m. The highest levels of drift losses were obtained with D-4 jet nozzles directed down on a helicopter, 5 g/ha on fallout sheets at 100 m. Some evidence of reduced airborne drift was apparent where the polymer thickening agent was used with aircraft and ground equipment. The test results indicate that significant reduction in drift losses were obtained with proper application equipment; however, the use of a polymer thickening agent reduced drift only slightly for certain applications.