The herbicide O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidothioate (DMPA) contains an asymmetric tetracovalent phosphorus. The d-isomer is much less active and the l-isomer more active than dl-DMPA in inhibiting seedling grass growth. Furthermore, low levels of dl-DMPA stimulate root growth of seedling wheat (Triticum vulgare L., var. Soft winter).

Under greenhouse conditions, jimsonweed (Datura stramonium) L. ♯3 DATST) grown in soil treated with vernolate (S-propyl dipropylthiocarbamate) was more sensitive to postemerence application of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] than jimsonweed grown in untreated soil or soil treated with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Vernolate followed by acifluorfen was more phytotoxic than acifluorfen alone. Bentazon applied to jimsonweed after a pretreatment with vernolate at 2.2 kg ai/ha was more effective than the same rate of bentazon applied alone. Trifluralin did not enhance the activity of acifluorfen or bentazon on jimsonweed. Laboratory studies showed that more acifluorfen was absorbed by vernolate-pretreated jimsonweed than by untreated jimsonweed. No differences in bentazon absorption between vernolate-pretreated and nontreated jimsonweed were measured.

Disking, relisting, cultivation and no repreparation were employed in repreparing for planting seedbeds that had received preemergence treatment with 3-(3,4-dichlorophenyl)1,1-dimethylurea (diuron). Only the relisting method of seedbed repreparation appeared hazardous with respect to crop injury from herbicidal residues. Retreatment with diuron tended to increase injury symptoms in replanted cotton but yields were not significantly reduced by retreatment. Early-season weed competition, preventable by preemergence treatment, appeared to be more hazardous to yields than slight to moderate herbicidal injury to the cotton. Cotton replanted on plots treated once or treated twice significantly outyielded that on untreated plots in one of the two years in which all plots were replanted.

A 4.6-m-long, segmented, flexible-pipe ropewick applicator was constructed to apply picloram (4-amino-3,5,6-trichloropicolinic acid) to leafy spurge (Euphorbia esula L. ♯ EPHES) and other weed species. Gauge wheels on each ropewick applicator segment permit height adjustments, and a loose, independent, vertical flexing action permits the segments to effectively traverse depressed or raised areas. The applicator was designed for use in pastures with rough, uneven terrain where it is difficult to uniformly wipe herbicide solution on plants with a rigid-pipe ropewick. The applicator was found to be durable and effective in applying picloram to leafy spurge.

Among 15 different herbicides tested for eradication of Turkey oak (Quercus laevis Walt.) over a period of four years on Lakeland fine sand in Florida, only monuron, diuron, and fenuron at minimal rates of 10 lb/A were effective. One full growing season after application was required for complete kill. Phenoxy compounds gave variable top-kill but not satisfactory control. AMS, dalapon, and four formulations of benzoic acid were ineffective in these tests.

Out of 13 different grasses, Pensacola bahiagrass (Paspalum notatum Flugge) and weeping lovegrass (Eragrostis curvula Schrad.) were best adapted to these deep sandy soils. Seedbed preparation was essential to obtain a good stand of either. After establishment, the lovegrass vigorously persisted throughout the experiment; the bahia also persisted but the lack of fertilization was extremely evident. Both grasses could be established satisfactorily on soil treated two years earlier with monuron or diuron at 10 lb/A.

Field and laboratory experiments were conducted in 1977 and 1978 to evaluate the movement and persistence in soil of metriflufen {methyl ester of 2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} under different conditions. In the field, delaying incorporation of metriflufen did not affect its activity in Taloka silt loam for either year as shown by bioassay with grain sorghum [Sorghum bicolor (L.) Moench]. Metriflufen activity in the soil persisted for 63 and 40 days after application in 1977 and 1978, respectively. In the laboratory, metriflufen moved through saturated soil columns to an average depth of 7.5 and 18.5 cm following the addition of 2.5 or 10 cm of water to the columns. In a growth chamber bioassay, grain sorghum growth in treated soil gave a dose-response in a range of 0.02 ppmw (I10), 0.09 ppmw (I50), and 0.38 ppmw (I90). When soil treated with metriflufen at 1 ppmw was incubated for specified times under soil moisture levels of 5, 15, or 25% and temperature regimes of 15, 25, or 35 C, soil incubated at 15 C for as long as 75 days completely inhibited grain sorghum growth regardless of the other treatment variables. Grain sorghum growth inhibition was reduced with incubation time and warmer temperatures for treated soil maintained at 5 and 15% moisture, but sorghum growth inhibition persisted for treated soil incubated under wet (25% moisture) conditions.

A fast and efficient method of evaluating soil incorporators consists of incorporating a fluorescent dye into the soil, taking soil samples, removing the dye by a solvent, and determining the dye concentration. Pontacyl Brilliant Pink B was the best dye for incorporation studies and a fluorometer was the analytical instrument.

The effects of residues of 16 herbicides used to control downy brome (Bromus tectorum L.) were studied in the greenhouse. Crested wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult.) was planted in soils collected from field plots sprayed 1 to 4 years previously. At the rates used, some residues were lethal to crested wheatgrass seedlings, some caused severe malformation and/or herbage yield reduction, while others had no adverse effects.

A tractor-mounted mist blower was as effective as a high-volume ground sprayer or an airplane sprayer for applying herbicides to control hardwoods in two tests in central Louisiana. Two lb/A of butoxyethanol ester of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were slightly better than one, and May treatments were more effective than August treatments.

Stands of Russian knapweed (Centaurea repens L.) were reduced over 80 per cent by several combinations of crops, cultivation and herbicides. Two of the best crop rotations in a 4-year trial were: (1) a short season of intensive cultivation and a mid-August seeding of bromegrass that was sprayed with 1 lb/A of butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D) during June and 1 or 1½ lb/A during August of the second and third years. (2) Bromegrass seeded with an oat companion crop sprayed with ⅓ lb/A of 2,4-D ester the first year and annual applications of 2,4-D in June and mid-August during the second and third years. The best use of non-selective herbicides in two 2-year trials was spring application of 4 lb/A of diethylamine salt of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) or 6 lb/A of diethylamine salt of polychlorobenzoic acid (PBA), plowing 10 days later, and a corn crop sprayed with ⅓ lb/A of 2,4-D ester followed by a spring-seeded oat crop sprayed with d13 lb/A of 2,4-D ester and postharvest application of 4 to 6 lb/A of 2,3,6-TBA and 6 to 8 lb/A of PBA, and plowing 10 days later. Reinfestation from established plants was not prevented, but annual application of 2,4-D prevented reinfestation from seedlings.

A time course study on the in vitro effect of 10–4 M (2,4-dichlorophenoxy)acetic acid (2,4-D) on the metabolism and incorporation of specific 14C-labeled glucose into pea (Pisum sativum L., var. Alaska) and corn (Zea mays L., var. Golden Cross) tissues showed a preferential release of C-1 as CO2 which was affected by 2,4-D. The glucuronic acid pathway was stimulated greatly in pea roots and slightly in corn stems; it was inhibited in corn roots. The pentose phosphate pathway was affected in an opposite pattern. The incorporation of both labeled carbon atoms into alcohol-insoluble residue was also affected by 2,4-D. The degree of effect, however, varied from pea to corn and from roots to stems. Analysis of the alcohol-soluble fraction revealed different effects of 2,4-D on labeling of some of the amino acids, an increase in fructose content, and an accumulation of malic acid.

Weed Scientists, like many other agricultural scientists and natural resource land managers, often engage in debate with other members of society about values and perceptions of food and fiber production. The focus of the debate is usually on the tools and tactics to grow crops, produce wood, or manage grazing land. Environmental ethical issues have dominated discussions among the membership of WSSA for decades. Examples include the decade-long debate over 2,4,5-T use in forestry and now water quality and human health concerns about atrazine use in agriculture. Ecology is a scientific discipline that seeks knowledge about the interactions of organism, their environments, and, more broadly, the effect of human activities on them. Because weeds are a consequence of how we grow food, the study of both ecological and human components of agroecosystems should allow weed scientists to construct management strategies that more fully address the production, environmental, and social implications of weeds and weeding.

A modification of an 8-ft, self-propelled combine for harvesting research plots of soybeans (Glycine max L.), sorghum [Sorghum bicolor (L.) Moench], and small grains is described. The combine facilitates efficient and precise harvesting of yield plots with considerable savings in time and labor.

Dalapon (2,2-dichloropropionic acid) was applied at 3.3 kg/ha during late May or early June to a well-established grass sward consisting of smutgrass [Sporobolus poiretii (R.&S.) Hitchc], pangolagrass (Digitaria decumbens Stent.), and bahiagrass (Paspalum notatum Flugge. ‘Pensacola’). Two cultural treatments, mowing or roller chopping, and two fertilizer treatments, 0 or N-P-K at 112-25-93 kg/ha were superimposed on the dalapon treatments at four different time intervals in a split plot design. Chopping or mowing 2 weeks after the dalapon treatment resulted in the highest bahiagrass ground cover and smutgrass control with a minimum amount of bare soil. Chopping tended to favor pangolagrass recovery, and mowing favored bahiagrass recovery. Fertilizer application increased pangolagrass ground cover 90-days after treatment, and smutgrass control after 1 yr. Fertilizer application 6 weeks after dalapon treatment generally increased pangolagrass ground cover and smutgrass control. Pangolagrass responded to fertilizer regardless of chopping or mowing. Mowing controlled more smutgrass than did chopping on the non-fertilized plots.

The most economical time to control invading noxious shrubs is at an early stage in the invasion, when stands are sparse. One method of doing this is with a ground spray rig (Fig. 1). With such a rig the problem is to get the guns out from the vehicle so that a reasonable-sized swath can be covered. The out-rigger apparatus described herein can be used to cover a swath of 50 feet where the brush is fairly dense, to 90 feet on sparser stands.

Field studies have shown primisulfuron to be more injurious to sugarbeet than nicosulfuron 1 and 2 yr after herbicide application. Experiments were initiated to determine if primisulfuron is more injurious to sugarbeet grown in a nutrient culture and if the difference in sugarbeet response is a result of greater uptake, translocation, or acetolactate synthase (ALS) site sensitivity with primisulfuron. Concentrations of primisulfuron and nicosulfuron that reduced sugarbeet growth by 50% were 1.9 and 8.9 μg ai L−1, respectively, at pH 6.5. The pH of the nutrient solution did not influence sugarbeet response to either herbicide. Uptake of primisulfuron was greater (3%) than that of nicosulfuron (1%). Translocation (expressed as a percent of uptake) of nicosulfuron was more rapid than primisulfuron. Fifty-seven percent of the absorbed nicosulfuron translocated out of the root during the 12-h pulse period, while an equal concentration of primisulfuron was not translocated out of the root until 48 h after pulsing. The total nicosulfuron translocated after 144 h was half that of primisulfuron. The nutrient solution taken up by sugarbeet in the 12-h pulse period was reduced by 41% in the presence of either herbicide compared to the untreated control. The ALS enzyme was a minimum of 15 times more sensitive to primisulfuron compared to nicosulfuron which may account for greater sugarbeet response to primisulfuron.

Combinations of MSMA (monosodium methanearsonate) with bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], DCPA (dimethyl tetrachloroterephthalate), or prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} were applied at various dates of treatment to bermudagrass [Cynodon dactylon (L.) Pers.] and Kentucky bluegrass (Poa pratensis L.) in the spring for large crabgrass [Digitaria sanguinalis (L.) Scop.] control. Bensulide controlled a higher percentage of weeds than did DCPA, regardless of treatment dates. When treatments were delayed until late April in Griffin and mid May in Blairsville, Georgia, large crabgrass control was improved from combinations of MSMA with bensulide compared to bensulide alone. Combinations of MSMA with DCPA improved large crabgrass control when applied in March and April at Griffin and in May at Blairsville. Combinations of MSMA with either bensulide or DCPA performed equally well whether applied as a single tank-mix treatment or as separate applications on the same day. Large crabgrass control was not improved at any date from combinations of MSMA with prosulfalin when compared with prosulfalin alone.

The experimental herbicide R-24191 [1-(m-t-butylacetamidophenyl)-3-methyl-3-methoxy urea] inhibited growth of Chlorella sorokiniana Shihira and Kraus, O2 evolution during CO2 fixation by Chlorella and isolated leaf cells of spinach (Spinacia oleracea L. ‘Winter Bloomsdale 769′), the photoreduction of NADP by isolated chloroplasts using water or hydroxylamine as the electron donor, the photoreduction of 2,6-dichloroindophenol by isolated chloroplasts, and O2 uptake by isolated chloroplasts using paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) as the electron acceptor. The phenylurea herbicide had no effect on the last reaction when ascorbate plus 2,6-dichloroindophenol were used as the electron donor. The results indicate that the site of the phenylurea inhibition was in photosystem II between water-splitting and photosystem I.