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).

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.

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.

The herbicide 2,4-D is commonly used for sucker control in hazelnut (Corylus avellana L.). However, the use of 2,4-D for sucker control has been implicated in delaying natural abscission in hazelnut. Hazelnuts naturally abscise and are collected from the orchard floor. Delays in abscission may reduce nut quality due to the onset of the rainy season, increasing mold and mud in the nuts. The effect of basal-directed applications of 2,4-D on hazelnut abscission, yield, and quality was assessed. In the first study, four basal-directed applications of 2,4-D (1.06 kg ae ha−1) did not affect hazelnut abscission, yield, or quality compared with glufosinate (1.1 kg ai ha−1) or manual pruning. In a second 3-yr study, a single yearly simulated drift of 2,4-D to the tree canopy at 0.06 and 0.6 mg L−1 increased the growing degree-day requirement from 50 to 141 to reach 50% hazelnut abscission, compared with the nontreated control. This is the equivalent of 5 to 15 calendar days. No effect was observed in the third year of the study when the simulated drift was not performed. No differences in abscission were observed with basal-directed applications of 2,4-D at rates up to 4.4 kg ha−1 when applied four times each season during all 3 yr of the study. Simulated drift reduced hazelnut yield by up to 37% and reduced the percentage of marketable nuts during 1 yr of the study. No effect on average kernel weight was observed. However, 2,4-D drift did delay hazelnut abscission, highlighting the importance of drift control measures.

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.

A laboratory spray cabinet was constructed of stainless steel with three compartments for separate dosage applications. Overhead spraying is accomplished in all three compartments by a single mobile nozzle activated by an air cylinder and cable drive. The system was designed so that test compounds could be applied safely and accurately at various rates on plants up to 1 m high. The cabinet has an air exchange and filtration system to prevent possible contamination of spray equipment, untreated test materials and the atmosphere.

Two experiments were conducted to determine the most effective herbicide treatments for fringed sagebrush (Artemisia frigida Willd.) control in rangelands. In the first study the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.1, 0.6, and 0.8 kg/ha; picloram + the propylene glycol butyl ether ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 0.1 + 1.1 kg/ha; the monoethanolamine salt of 3,6-dichloropicolinic acid at 1.1 kg/ha; 3,6-dichloropicolinic acid + 2,4-D at 0.6 + 1.1 kg/ha; and the dimethylamine salt of dicamba (3,6-dichloro-o-anisic acid) + 2,4-D at 0.6 + 1.1 kg/ha applied in late summer at flowering, showed the greatest potential for fringed sagebrush control. In the second experiment, the potassium salt of picloram at 0.3 kg/ha applied either in the spring or late summer gave 94 to 100% fringed sagebrush control, respectively, 1 yr after application. Control of fringed sagebrush had declined to 50% 3 yr after application. Production of perennial grasses from plots receiving picloram at 0.3 kg/ha in 1976 was increased by 410 kg/ha in 1977, 450 kg/ha in 1978, and 430 kg/ha in 1979 over that of the untreated plots.

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.

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.

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.

Weeds have plagued man in his agricultural pursuits since biblical times in spite of backbreaking efforts to control them by hand and mechanical methods. At this second meeting of the Weeds Journal of Weed Society of America it appears appropriate to review briefly some of the modern accomplishments in weed control and to take stock of future needs.

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.

Madrone (Arbutus menziesii Purch.) and tanoak (Lithocarpus densiflora (H & A) Rehd.) are often considered undesirable along the Pacific Coast. These weed trees are removed to increase forage production; to remove competitors of more valuable timber trees, especially Douglas fir (Pseudotsuga menziesii (Mirb) Franco); or to obtain firewood or charcoal. Tanoak is occasionally cut for tanbark harvest. Control of stump sprouting following cutting would be desirable.

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.