Perennial ryegrass is overseeded in bermudagrass and Kentucky bluegrass to improve turf quality, but selective control may be warranted for transition back to monostand turfgrass. Flucarbazone–sodium controls perennial ryegrass in bermudagrass and Kentucky bluegrass, but the physiological basis of selectivity has received limited investigation. Greenhouse and laboratory experiments were conducted to evaluate efficacy, absorption, translocation, and metabolism of flucarbazone–sodium in these grasses. Flucarbazone–sodium reduced perennial ryegrass shoot mass from the nontreated an average ≈ 22 times and 3 times more than bermudagrass and Kentucky bluegrass at 4 wk after treatment, respectively. In laboratory experiments, foliar and root absorption of 14C–flucarbazone–sodium were similar among species. Bermudagrass distributed ≈ 25% more foliar-absorbed 14C to nontreated shoots than Kentucky bluegrass and perennial ryegrass. From root applications, all grasses averaged 84% distribution of 14C to shoots. Bermudagrass and Kentucky bluegrass metabolized 100% and 74% of 14C–flucarbazone–sodium at 1 d after treatment (DAT), whereas perennial ryegrass metabolism measured 44, 58, and 65% at 1, 3, and 7 DAT, respectively. Bermudagrass, Kentucky bluegrass, and perennial ryegrass had 4, 4, and 2 metabolites after 7 d, respectively. Results suggest differential metabolism of flucarbazone–sodium is attributed to selectivity for controlling perennial ryegrass in bermudagrass and Kentucky bluegrass.

Picloram (4-amino-3,5,6-trichloropicolinic acid), 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and dicamba (3,6-dichloro-o-anisic acid) were sprayed at 0.28 kg/ha on honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] and huisache [Acacia farnesiana (L.) Willd.] seedlings 1, 2, 4, 8, 12, and 16 weeks after emergence from seed under greenhouse conditions. Picloram or 2,4,5-T killed 73% or more of the honey mesquite up to 8 weeks after emergence, but the percent killed declined thereafter. Picloram killed more than 90% of the huisache seedlings when applied from 1 to 8 weeks after emergence. Less than 60% of the honey mesquite or huisache seedlings were killed with dicamba at any treatment date. Clipping the plants at the soil level resulted in high mortality (96 to 100%) of both species 1 to 2 weeks after emergence. Treating regrowth of clipped 1-year-old honey mesquite and huisache with 0.28 kg/ha of picloram, dicamba, or 2,4,5-T produced results similar to those obtained from plants grown from seed.

Experiments were conducted from 1989 to 1991 on two silt loam and two clay soils to determine the effect of herbicides applied to the previous crop on growth and yield of rice. All herbicides were applied preplant-incorporated at recommended rates adjusted as needed for soil texture. Rice was planted the following year. Imazaquin, imazethapyr, alachlor, metolachlor, clomazone, trifluralin, and atrazine did not injure rice the year following application. Norflurazon was the only herbicide to injure rice on silt loam soils, with injury at one silt loam location in one of two years. Norflurazon and fluometuron residues caused rice injury on clay soils, and chlorimuron residues caused injury in one year on a day soil. This chlorimuron carryover injury was from August-planted soybean but did not occur from June-planted soybean. Norflurazon, fluometuron, and chlorimuron temporarily reduced rice dry matter early in the season. No herbicide reduced either rough rice or percent head rice yield on any of the soils.

Preplanting applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] with and without trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were made for 5 years in irrigated cotton (Gossypium hirsutum L.). All treatments containing trifluralin temporarily stunted cotton. In two of the 5 years, trifluralin reduced diuron injury to cotton seedlings which resulted in better crop stands. The trifluralin-diuron combinations resulted in better weed control at harvest than either herbicide alone. The 5-year average yield of cotton was greater with trifluralin-diuron combinations than with the same rates of diuron alone.

Field studies were conducted in Mississippi on a Marietta loam during 1988, 1989, and 1990, and in Tennessee on a Statler loam during 1988 and 1989, to determine effect of tillage on chlorimuron persistence. A corn shoot bioassay was conducted to determine bioavailable chlorimuron in the soil. Tillage system affected chlorimuron persistence only in 1989 at Tennessee. Chlorimuron half-life was 10 to 31 d longer in both tillage systems in Mississippi in 1988 compared to 1989 and 1990, probably due to low soil moisture immediately after application in 1988. In Tennessee, chlorimuron half-life was 71 d shorter in the no-till system in 1988 compared to 1989. Differences did not occur between locations in the conventional tillage system in 1989. Differences in chlorimuron persistence between years and locations were most often attributed to soil water and temperature. Soil pH differences between the two locations did not consistently affect chlorimuron persistence.

The locoweeds, woolly loco and silky crazyweed, contribute to livestock poisoning in the western United States. Differences in response of these two locoweeds to foliar-applied picloram and metsulfuron was investigated by evaluating differences in herbicide uptake, translocation, and metabolism. Silky crazyweed compared to woolly loco was more than 10 times as sensitive to increasing rates of either herbicide. The two species absorbed 8 to 15%, and 11 to 17% of applied picloram and metsulfuron, respectively. Translocation of picloram and metsulfuron out of treated leaflets of either species was less than 3% of that absorbed after 96 h. Approximately 70 and 100% of the absorbed herbicides remained as picloram and metsulfuron, respectively, in both species. Therefore, differences in picloram or metsulfuron uptake, translocation, and metabolism appear inadequate to account for the differential response to each herbicide by the two locoweed species. Selectivity differences between these locoweed genera to picloram and metsulfuron most likely are due to sensitivity differences at sites of action.

Greenhouse and field experiments were conducted to determine the effectiveness of dichlormid, R-29148, CGA-92194, flurazole, naphthalic anhydride, and MON-5500 as herbicide antidotes for triallate in wheat and to determine triallate antagonism by seed-applied fungicides and insecticides. Seed treatment of MON-5500 at 0.063% wt/wt was the most effective antidote for triallate in wheat in both greenhouse and field. Dichlormid and R-29148 at 0.5% wt/wt were more effective as antidotes for triallate in wheat than either CGA-92194 or naphthalic anhydride. Flurazole, as a seed treatment, did not reduce triallate injury to wheat Dichlormid or R-29148 at 2.2 kg ai ha–1 applied broadcast to soil and incorporated reduced injury to wheat from triallate at 1.1 kg ai ha–1 and also reduced injury to oats from 0.3 kg ha–1 triallate. Seed treatments of carboxin at 0.2% wt/wt or imazalil at 0.008% wt/wt antagonized triallate and decreased injury to wheat from triallate at 0.6 kg ha–1. Maneb plus lindane or mancozeb treatment of wheat seed increased injury from triallate.

Red clover (Trifolium pratense L.) was direct seeded into a grass sod after spraying with dalapon (2,2-dichloropropanoic acid), glyphosate [N-(phosphonomethyl) glycine], or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at rates of 5.6, 2.2, and 0.6 kg ai/ha respectively. Dalapon applied a few days prior to planting did not improve red clover stands in comparison to seeding in unsprayed sod. Applying glyphosate a few days prior to seeding in spring and summer invariably increased red clover stands, but paraquat was effective in only one of four spring or summer applications. Glyphosate applied the fall preceding a spring or summer seeding produced red clover stands superior to those after all spring treatments. Where glyphosate or paraquat was applied, water content of the upper 20 cm of the soil profile was greater during the first 10 days after treatment, relative to unsprayed plots or those treated with dalapon. By 30 days after application, the glyphosate-treated sods used less soil water than those treated with paraquat. Applications of glyphosate and paraquat greatly suppressed water utilization by oats (Avena sativa L.) in the greenhouse, based on water potential of the potting soil. Dalapon had little effect on water use by oat seedlings in the greenhouse.

Quackgrass [Agropyron repens (L.) Beauv.] was controlled by spring application of pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] in 1970 and 1971, but when spring rainfall was below nornal in 1973, only pronamide applied the previous fall gave control. Terbacil (3-tert-butyl-5-chloro-6-methyluracil) gave 90% control of quackgrass for 2 yr at 2.2 kg/ha. Some control continued for 3 yr at 4.5 kg/ha. Three applications of glyphosate [N-(phosphonomethyl)glycine] at 3 kg/ha applied during a 2-yr period controlled quackgrass 97 to 100%. Phytotoxicity was not observed on 14-yr-old highbush blueberries (Vaccinium corymbosum L.) from pronamide or terbacil, on 4-yr-old blueberries from pronamide, or on 2-yr-old rhododendrons (Rhododendron × ‘A. Bedford’) from dichlobenil (2,6-dichlorobenzonitrile), pronamide, or directed sprays of glyphosate or amitrole (3-amino-s-triazole).

Dalapon (2,2-dichloropropionic acid), injurious to Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and grand fir (Abies grandis (Dougl.) Lindl.) when used alone for weed control, was used with safety and even with beneficial effects when combined with atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)-s-triazine] and 2,4-D, [(2,4-dichlorophenoxy) acetic acid] at rates of up to 3.36 and 4.48 kg/ha, respectively. Harmful effects of dalapon were masked at rates up to three times those used for adequate control of grasses. This suggests a type of selectivity previously unreported. Interpretation of herbicide effects and interactions was made possible with an analytical model that separated effects of vegetation from those of herbicides on a causal basis. This technique included two-dimensional adjustment of the base of reference for a four-dimensional response-surface equation. This surface fit observed data as well as a single multiple-regression equation, which included all variables. This approach, however, estimated herbicide parameters with appropriate consideration of environmental data and permitted interpretation with respect to cause.

In order to find the most effective and economical method of incorporation, six preplant herbicides for cotton (Gossypium hirsutum L.) were incorporated with a tandem disk or field cultivator, or sprayed on unbedded soil prior to bedding with a disk bedder. These treatments were compared to incorporating sprayed beds with a rolling cultivator and no incorporation. A mixed population of pigweed (Amaranthus hybridus L. # AMACH and Amaranthus retroflexus L. # AMARE) was present each year. There was no significant difference in pigweed control among incorporation with a disk, field cultivator, or rolling cultivator. Puncturevine (Tribulus terrestris # TRBTE) and barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] were controlled best following rolling cultivator incorporation. Cotton lint yields were not affected by incorporation methods or herbicides. Economic analysis and weed control indicate that the field cultivator was the best way of incorporation.

Weed Science is a relatively young but challenging and dynamic discipline. It includes all aspects of combating weeds and reducing their undesirable effects on mankind–directly or indirectly. The need for effective weed control is not new; it has prevailed since the primitive beginning of crop culture. It has evolved into a strong discipline, however, only since World War II, stimulated by a pressing need for more economic weed control. In response to this need, numerous advances have been made that help to produce higher crop yields at lower cost. Herbicides have become common, intensive research and educational programs have been established, and Weed Science has taken its rightful place as a respected discipline in the academic and industrial communities.

Bean (Phaseolus vulgaris L., var. Tendercrop) plants treated during germination with 100 ppm 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) were indistinguishable from untreated plants until 5 days after seedling emergence. Chlorosis began at the leaf margins, progressed inward, and became more severe until the leaves became necrotic and died. Similar symptoms were observed on leaves of plants treated with 25 and 50 ppm, but they appeared 4 to 10 days later. The light-microscope study of leaf tissue revealed that chloroplast form and arrangement were altered by pyrazon treatment. Chloroplasts in leaves of treated plants became round and swollen rather than discoid, contained no starch, aggregated in clumps, and developed an affinity for safranin stain.

Yields of birdsfoot trefoil (Lotus corniculatus L.) and red clover (Trifolium pratense L.) were increased during establishment after herbicide treatments. All treatments, which included preplanting application and incorporation of EPTC (S-ethyl dipropylthiocarbamate) at 2, and 4 kg/ha in all combinations with postemergence applications of dinoseb (2-sec-butyl-4,6-dinitrophenol) at 0.25 and 0.5 kg/ha, controlled weeds and increased yields over those of untreated plots during a 2-yr period. EPTC and dinoseb treatments alone and in combinations were economical in birdsfoot trefoil, using the cost for weed control and the value of the extra forage. However, with red clover only dinoseb proved economically feasible at hay prices less than $80/metric ton.

Over a 3-yr period 10 herbicides were tested alone or in combination for control of weeds and for effects on growth of nursery stock in containers. Annual bluegrass (Poa annua L.) was controlled by norea [3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea], alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], and combinations of diphenamid (N,N-dimethyl-2,2-diphenylacetamid), trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] plus simazine [2-chloro-4,6-bis(ethylamino)-s-triazine]. Bittercress (Cardamine oligosperma Nutt.) was controlled by simazine, oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one], and norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone]. Mouseear chickweed (Cerastium vulgatum L.) was controlled by dichlobenil (2,6-dichlorobenzonitrile) and norflurazon, and common groundsel (Senecio vulgaris L.) was controlled by dichlobenil and norflurazon. Some of the treatments decreased growth of certain nursery cultivars.

The effects of chlorimuron as related to application timing were evaluated on sicklepod and soybean in the glasshouse. Plants were sprayed with chlorimuron at 8.8 g ai ha–1 at 14, 21, 28, and 35 days after planting (DAP). Early (14 DAP) chlorimuron application reduced sicklepod dry weight, leaf area, and water use to levels significantly less than those of plants treated at 28 and 35 DAP. Soybean dry weight and leaf area were not affected by chlorimuron. However, soybean water use was initially reduced at application timings of 28 DAP or earlier but recovered by 4 weeks after treatment (WAT). Sicklepod net assimilation rate (NAR) and relative growth rate (RGR) were reduced by chlorimuron regardless of application timing while soybean was not affected.

The effect of the herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on photosynthesis, respiration, anthocyanin formation and leaf ultrastructure of corn (Zea mays L. ‘Pioneer 3780’) was studied following pre- or postemergence applications. Total photosynthesis and dark respiration were measured with an infrared CO2 analyzer in an open air flow system 12, 18, and 24 days after preemergence treatment with 0, 0.56, 1.12, and 2.24 kg/ha of buthidazole. The 0.56 and 1.12 kg/ha preemergence treatments had no effect on total corn photosynthesis even 24 days after treatment, whereas buthidazole at 2.24 kg/ha inhibited photosynthesis as early as 12 days. Total photosynthesis and dark respiration were also measured in whole plants, 30 cm tall, before herbicide application and 4, 24, 48, and 96 h after postemergence treatment with buthidazole at 0, 0.28, 0.56, 0.84, and 1.12 kg/ha. Following postemergence treatment, buthidazole inhibited total corn photosynthesis at any rate examined as early as 4 h after treatment. Neither pre- or postemergence buthidazole applications influenced respiration with the exception of a transitory increase caused by 0.56 kg/ha 12 days after preemergence treatment and by 0.84 and 1.12 kg/ha 4 h after postemergence treatment. Transmission electron micrographs revealed that buthidazole applied postemergence at 0.28 and 1.12 kg/ha reduced or prevented the accumulation of starch in bundle sheath chloroplasts as early as 24 h after treatment. Ultrastructural disruptions in some mesophyll chloroplasts of treated corn plants were also evident. Preemergence application of buthidazole at rates of 0.28, 0.42, 0.56, and 1.12 kg/ha inhibited anthocyanin formation indicating an alteration in corn metabolism.

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’?

Seeds of Pennsylvania smartweed (Polygonum pennsylvanicum L.), quackgrass (Agropyron repens L. Beauv.), yellow foxtail (Setaria lutescens L. Beauv.), and wild mustard (Brassica kaber (DC) L. C. Wheeler) were studied to determine if histochemical differences existed in seeds of dormant and non-dormant weed species. The hulls (seedcoat) of yellow foxtail and seedcoats of wild mustard and quackgrass had distinct inhibitory effects on germination. Endosperm tissue in wild mustard and Pennsylvania smartweed also inhibited embryo growth in these species. Results obtained from specific staining techniques on seed sections 10μ thick for identification and determination of distribution of proteins, lipids, carbohydrates, and lignin in dormant and germinating seeds suggested that possible mechanisms of seed dormancy are: (a) lower protein content in seed tissues of wild mustard; (b) higher lignification in hull of foxtail and endosperm of Pennsylvania smartweed; (c) lower sterol content in embryo of wild mustard and Pennsylvania smartweed; (d) high cellulose content in hull of foxtail and endosperm of Pennsylvania smartweed. Excised embryos from dormant seeds of Pennsylvania smartweed showed a measurable amount of growth in White's standard agarnutrient. Germinating embryos of wild mustard and quackgrass were larger than those in dormant seeds; therefore, immaturity of embryos might contribute to dormancy in these species.