Studies with plant growth-regulators are severely handicapped unless methods are available for quantitative determinations of these chemicals. Beginning with the classical work of Went, several techniques have been developed to obtain a quantitative measure of plant growth-regulating chemicals. Brown and Weintraub, Hitchcock and Zimmerman and Frankton have discussed the use of biological assays as quantitative tests for various hormone-type chemicals. Thus far, the only biological methods developed beyond the semi-quantitative stage are those depending on cell elongation in shoots, inhibition or elongation of roots, and the stimulation of ovary development.

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.

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.

According to Bonner, at least three different oxidase systems may be involved in the final step of the transfer of electrons to oxygen. Each of the terminal oxidases has been shown to occur in many plants and in many relative combinations.

Growth of Oxalis cernua Thunb. was determined in different temperature regimes. Growth occurred in the 55 to 75 F range. Temperature variation promoted growth. Bulbs sprouted more rapidly and uniformly after storage at 35 F than after storage at 95 F. The weed probably is best adapted to areas with winter soil temperatures between 55 and 75 F.

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.

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.

Absinth wormwood (Artemisia absinthium L.), a perennial, native to Europe, has become abundant during the last decade in several locations in western Canada. Reports received during the Saskatchewan Weed Survey suggest that at least some of the introductions into this area were by immigrants from Europe, who believe it to have medicinal properties. Silver-grey in color and covered with fine hairs, the herbaceous stem grows to a height of 2 to 4 ft, often branching profusely. The leaves are up to 5 in. long and are two to three times divided into lanceolate segments. Numerous, drooping heads, about 3/16 in. in diameter, develop in leafy panicles. Yellow or purple florets are borne on a hairy base. The whole plant has a strong, penetrating odor, common in other species of this genus. In Europe it is used as a stimulant (tea and liquor).

Field studies were conducted to determine the influence of annual herbicide treatments plus cultivation on weed populations and corn yields in ridge-till corn during a 3-yr period at Mitchell, NE, and a 7-yr period at North Platte, NE. When the experiment was initiated at North Platte, no weeds were present before corn planting. It took 4 yr before triazine-resistant kochia became a problem before corn planting in plots treated with atrazine, but these were controlled by other operations prior to corn harvest. In the cultivated check, green foxtail densities before harvest increased from 0 in 1985 to 32 plants 100 m−2 in 1991. Annual applications of dicamba plus 2,4-D 10 d early preplant followed by cultivation controlled triazine-resistant kochia and velvetleaf, but common lambsquarters, nightshade species, and green foxtail increased. Volunteer corn was controlled with cultivation. After 3 yr at Mitchell, the annual weed population increased 10-fold in the cultivated check. Thus, corn yields were reduced 64% with two cultivations compared with an annual early preplant application of dicamba plus 2,4-D followed by alachlor plus cyanazine PRE and two cultivations. With two cultivations under low annual weed populations at North Platte, grain yield from the cultivated check treatment was not different from annual treatments of herbicides after 7 yr. Metolachlor plus atrazine occasionally caused a reduction in corn grain yields.

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.

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.

Three herbicide treatments were evaluated for use under clear polyethylene mulch and three types of row covers (spunbonded polyester, double-slitted polyethylene, and perforated polyethylene). Treatments included combinations of bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino]ethyl]phosphorodithioate} and naptalam {2-[(1-naphthalenylamino)carbonyl]benzoic acid}, and cinmethylin {exo-1-methyl-4-(1-methylethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo [2.2.1] heptane} alone and in combination with naptalam. In 1985 and 1986, all herbicide treatments controlled more than 95% of carpetweed (Mollugo verticillata L. # MOLVE) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], except for the combination of bensulide plus naptalam in 1986, which controlled only 73 to 85% of these weeds. In both years, all herbicide treatments reduced crop vigor at 3 weeks but not at 7 weeks after transplanting. Total yield was not different with any of the herbicide treatments in 1985 and 1986. However, in 1986, yields were greater from the bensulide plus naptalam treatment than for the weed-free control. Herbicide treatment did not affect early yields in 1985, but the bensulide plus naptalam treatment was greater than all others in 1986. The use of row covers did not increase herbicide-induced crop injury over that of clear mulch alone. Greenhouse studies indicated that soil-applied cinmethylin reduced muskmelon root and shoot weight. Foliar applications reduced muskmelon shoot weight.

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.

A 3-year field experiment was initiated in 1967 to study the effects of herbicides in combination with the systemic insecticide, O,O-diethyl S-2-[(ethylthio)ethyl] phosphorodithioate (disulfoton) on cotton (Gossypium hirsutum L.). Herbicide treatments of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl)urea (fluometuron), 3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea (norea), 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin), and α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) did not significantly affect yield of weed-free cotton while disulfoton treatment significantly increased yield over the 3-year period. Yield with disulfoton was negatively correlated with number of thrips (Thripidae sp.). No interaction occurred between herbicides and disulfoton on yield, and only in 1 year was there an effect on stand.

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 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 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.