The nonionic surfactants Tween 20 [oxysorbic (20 POE) polyoxyethylene sorbitan monolaurate] and Tween 80 [oxysorbic (20 POE) polyoxyethylene sorbitan monooleate] at concentrations of 0.05, 0.1, 0.2, and 0.4% v/v stimulated germination of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] seeds in petri dishes. Stimulation occurred under both 30/20 and 25/15 C diurnal temperature cycles whether or not light was supplied during the 8-h high-temperature portion of the cycle. Barnyardgrass responded most to treatment under environmental conditions in which untreated seeds germinated the least. A 0.1% surfactant concentration often stimulated germination of weed seeds as effectively as did higher concentrations. Germination of redroot pigweed [Amaranthus retroflexus L. # AMARE] seeds was inhibited by Tween 80 in the light under both the low- and high-temperature regimes and by Tween 20 at low temperature in the light. Germination of tumble pigweed (Amaranthus albus L. # AMAAL) seeds was inhibited by both surfactants in the high-temperature regime whether or not light was supplied. Common purslane (Portulaca oleracea L. # POROL) seeds were insensitive to treatment.

In many areas of the southwestern states where cotton is a major crop, the use of 2,4–dichlorophenoxyacetic acid (2,4–D) is hazardous. Its use is restricted by law in many localities during the growing season. In these areas many perennial broad-leaved weeds which are susceptible to 2,4–D, at least to some degree, grow in abundance. Because of extreme arid conditions and other factors these weeds have not responded favorably to soil sterilants. There is urgent need for more effective herbicides for these weeds.

Three methods of applying linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] with trifluralin (α,α,α-triflu-oro-2,6-dinitro-N,N-dipropyl-p-toluidine) were compared for control of annual weeds in furrow-irrigated cotton (Gossypium hirsutum L. ‘Deltapine 16′). The linuron-trifluralin combinations controlled annual weeds effectively until harvest. There was no difference in cotton yield, boll components, or fiber properties among the three methods of applying combinations of linuron and trifluralin.

Laboratory and growth room experiments were conducted to determine effects of CGA-133205, oxabetrinil, and flurazole on grain sorghum hybrids ‘DeKalb 46’ and ‘DeKalb 48’ after the seed were treated with the herbicide safeners and stored for up to 24 wk at various relative humidity levels. Each safener treatment had an adverse effect on grain sorghum seed as reflected by fewer normal seedlings at 4 d when averaged over storage time and relative humidity levels. Flurazole and oxabetrinil increased the number of ungerminated seed of both hybrids, and 0.4 and 0.8 g ai kg–1 CGA-133205 increased ungerminated seed of DeKalb 46. At ≥ 8 wk after storage, a reduction in germination was observed for seed treated with flurazole or oxabetrinil compared to seed stored without safener. This reduction also occurred with 0.4 and 0.8 g kg–1 CGA-133205, but only at 24 wk after storage. Each safener treatment minimized reduction in seedling shoot fresh weight by herbicides compared to the no-safener check through 24 wk after storage.

Greenhouse grown honey mesquite (Prosopis juliflora (Swartz) D.C. var. glandulosa (Torr.) Cockerell), huisache (Acacia farnesiana (L.) Willd.), and whitebrush (Aloysia lycioides Cham.) and field grown honey mesquite, huisache, whitebrush, live oak (Quercus virginiana Mill.), Arizona ash (Fraxinus velutina Torr.), and winged elm (Ulmus alata Michx.) were defoliated at several intervals following spray treatments with 4-amino-3,5,6-trichloropicolinic acid (picloram), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), or [(4-chioro-o-tolyl)oxy]acetic acid (MCPA). The time required by leaves to be retained on the plant after spraying to give maximum canopy reduction or death of plants varied among species. In most species, however, herbicide absorption and transport were complete within a 4-day period or less as compared to undefoliated treated plants.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] applied with simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] reduced by 47 to 82% the severity of simazine symptoms on California privet (Ligustrum ovalifolium Hassk.), staghorn sumac (Rhus typhina L.), and ‘Moonlight’ broom (Cytisus X praecox Bean). Oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) had a similar but smaller effect (40% reduction) when applied with simazine on broom in a field experiment and an effect equal to napropamide with simazine on privet in a greenhouse experiment. Both napropamide and oryzalin prevented some of the growth reduction from simazine on privet, broom, and ‘Baltic’ ivy (Hedera helix L. ‘Baltica’) in field experiments. In the greenhouse study with privet, napropamide prevented much of the growth-reducing effects of simazine on both shoots and roots of privet. Oryzalin appeared to have a similar effect.

The selective action of chloroxuron [3-(p-(p-chlorophenoxy)phenyl)-1,1-dimethylurea] on tolerant soybean [Glycine max (L.) Merr. ‘Kent’] and susceptible tall morningglory [Ipomea purpurea (L.) Roth] was studied using root and foliar applications. In root uptake studies with carbonyl-14C-chloroxuron, soybean roots contained greater than 90% of the total absorbed radioactivity; whereas tall morningglory roots contained approximately 60% of the total absorbed radioactivity. Leaves of 1, 2, and 3-wk old soybean plants contained 0.8, 3.7, and 3.5% of the total radioactivity, respectively; whereas leaves of tall morningglory plants of corresponding age contained 29.1, 33.0, and 37.4% of the total radioactivity. Metabolism from root uptake of both species was similar; and metabolites were identified as approximately 85% chloroxuron, 13% 3-(p-(p-chlorophenoxy)phenyl-1-methylurea (Compound II), and 2.5% 3-(p-(p-chlorophenoxy)phenylurea (Compound III) in 3-wk old plants. In a nutrient solution containing 5.6 × 10−6M chloroxuron, soybean plants with roots intact were tolerant; whereas plants with roots detached were susceptible indicating the importance of differential translocation for selective action from root uptake. Following foliar spray and washing of 2-wk old plants, tall morningglory foliage absorbed about two times more radioactivity than soybean foliage. Further, 18 hr after foliar application, chloroplasts isolated from tall morningglory contained twice as much 14C-chloroxuron as soybean chloroplasts. Metabolite concentrations recovered from foliar treatment of both species were similar; and metabolites were identified as 88.1 to 92.2% chloroxuron, 6.4 to 8.6 % Compound II and 0.5 to 1.7% Compound III.

Orchardgrass (Dactylic glomerata L.) and Kentucky bluegrass (Poa pratensis L.) were used as test species to study the phytotoxicity of mixtures of 2,2-dichloropropionic acid (dalapon) and dimethylarsinic acid (cacodylic acid). A technique involving ED50 values, a shortened graphic procedure, and probit transformations was developed. Mixtures in which cacodylic acid was in excess indicated synergistic effects on bluegrass and additive effects on orchardgrass. Dalapon in excess in the mixtures appeared to have had an antagonistic effect on cacodylic acid. Orchardgrass was more tolerant to cacodylic acid than bluegrass.

In tropical and subtemperate regions of the world, farmers plant vegetables and other crops in a vast array of cropping systems that often involve more than one crop being grown on the same parcel of land in a year. Weed communities within each cropping system shift depending on physical and climatic factors and the specific crop and weed management practices employed. Modern weed management strategies involve combinations of crop production practices and specific weed control technologies intended to reduce weed competition, thereby shifting the competitive balance in favor of the crop. Weed research and, training efforts, therefore, must focus on the entire cropping system with emphasis on year-round and multi-year management of weed communities.

Soybean cyst nematode (SCN) is one of the most yield limiting pathogens in U.S. soybean production. Henbit and purple deadnettle are winter annual weeds shown to facilitate SCN reproduction after crop harvest in the eastern Corn Belt. These weeds, along with volunteer soybean that germinates in autumn after harvest, are common to postharvest soybean production fields and provide an opportunity for SCN reproduction and population increase outside of the typical soybean production season. The objective of this experiment was to determine if autumn removal of these weeds and volunteer soybean can influence the winter weed seedbank, plant biomass, and SCN population densities. Microplots were established with or without Lamium spp. and volunteer soybean, and four winter weed removal timings (none, October, December, and May). Dry weights of autumn Lamium spp. were reduced 50% in October when grown in competition with volunteer soybean. SCN juveniles were found in henbit roots at higher densities in October (42 per gram of root) than December (5 per gram of root) and were also found in the roots of volunteer soybean (14 per gram of root) in October. SCN egg population densities were 50% lower in August after the summer fallow period. The results of this experiment suggest that autumn removal of winter annual weeds and volunteer soybean did not reduce SCN populations.

Recommended rates of glyphosate for noncultivated areas destroy the aboveground shoots of the perennial plant leafy spurge. However, such applications cause little or no damage to underground adventitious buds (UABs), and thus the plant readily regenerates vegetatively. High concentrations of glyphosate, applied under controlled environmental conditions, have been shown to cause sublethal effects in UABs of leafy spurge that produce stunted and bushy phenotypes in subsequent generations of shoots. We treated leafy spurge plants in the field with glyphosate (0, 1.1, 3.4, or 6.7 kg ai ha−1) to determine its effects on vegetative growth from UABs and on molecular processes. The number of shoots derived from UABs of glyphosate-treated plants was significantly increased compared to controls in subsequent years after application, and new shoots displayed various phenotypical changes, such as stunted and bushy phenotypes. Quantifying the abundance of a selected set of transcripts in UABs of nontreated vs. treated plants (0 vs. 6.7 kg ha−1) indicated that glyphosate impacted molecular processes involved in biosynthesis or signaling of tryptophan or auxin (ARF4, CYP79B2, PIN3, TAA1, TRP6, YUC4), gibberellic acid (GA1/CPS1, GA2/KS), ethylene (ACO1, ACS10), cytokinins (AHP1, AK2, CKX1), and the cell cycle (CDC2A, CDC2B, CYCD3;1). Glyphosate-induced effects on vegetative growth and transcript abundance were persistent for at least 2 yr after treatment. Determining the molecular mechanisms associated with vegetative reproduction in leafy spurge following foliar glyphosate-treatment could identify limiting factors or new targets for manipulation of plant growth and development in perennial weeds.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] is a preemergence herbicide used for the control of most annual grasses and many annual broadleaf weeds. Its influence on the uptake and translocation of N, P, K, Ca, Mg, Cu, Fe, and Zn by four plant species was observed. Napropamide influenced, in some cases dramatically, the uptake and movement of the essential elements, but its influence was not consistent from one type of plant to another.

A study was made with glucose-1-C14, glucose-6-C14, and glucose U-C14 to determine quantitatively the effects of 2,2-dichloropropionic acid (dalapon) on glucose utilization in roots and shoots of one-week-old barley seedlings. An attempt also was made to determine the major pathway of glucose metabolism involved. Dalapon apparently did not change the normal pathway of glucose metabolism but interferred with glucose utilization as evidenced by differences in radioactivity of sugars and organic acids. Partial blocks may be operative initially at the beginning of the glycolytic pathway and subsequently in the Krebs cycle.

Wet tropical forests have a high diversity of woody species which cause problems in sampling and analysis of data regarding herbicidal effectiveness. Three simplified sampling procedures were tested to determine their reliability in providing an estimate of whole-plot defoliation from broadcast applications. A procedure using a 50-tree sample including all species will provide the most reliable data.

A laboratory assay method was developed for studying pricklypear (Opuntia sp.) responses to herbicides. Herbicidal translocation from one pad to another and lateral translocation across a pad appeared to be very slight. Pads were killed when a butoxy ethanol ester, a propylene glycol butyl ether ester, or a 2-ethylhexyl ester formulation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was applied to only one side. Increasing temperatures from 21 to 43 C increased the rate of killing pads. Concentrations of 2,4,5-T at 8 lb aehg of solution usually killed the pad at temperatures above 21 C. Concentrations of 2,4,5-T at 4 lb aehg or less had little effect on the pads. Relative humidity level had little effect on 2,4,5-T activity, but the activity of a propylene glycol butyl ether ester of 2,4-dichlorophenoxyacetic acid (2,4-D) was more effective at the 90 to 95% level than at levels ranging from 30 to 75%. Water, diesel oil, and three diesel oil:water mixtures had little effect on 2,4,5-T toxicity. More toxic effects were shown by 2,4,5-T than 2,4-D. The propylene glycol butyl ether ester, the butoxy ether ester, and the 2-ethylhexyl ester of 2,4,5-T were equally effective on pricklypear at the same concentrations.

Effects of difenzoquat on wild oats grown under controlled environmental conditions were studied. Seedling height and fresh weight were significantly reduced 5 days after postemergence treatment. Dose-dependent increase in cell membrane permeability was detected after a 12-h exposure to the herbicide. Scanning electron micrographs showed normal leaf hairs and cuticular wax but swollen guard cells 10 days after treatment. Ultrastructural changes occurred before the visible symptoms. The primary effect of difenzoquat appears to be the disruption of the tonoplast and plasmalemma. The tonoplast showed greater damage than the plasmalemma. Secondary effects included damage to mitochondria and chloroplasts. Mitochondria were swollen and often ruptured, but the effect did not increase with the duration of exposure. Chloroplasts became spherical in shape, and their contents were also affected. The changes included: accumulation and then disappearance of starch granules, swelling of frets, fusion of granal thylakoids, detachment and then rupture of the outer membrane of the envelope, and clumping of ribosomes. By contrast, natural senescence caused greater injury of the plasmalemma than the tonoplast, a marked increase in size of plastoglobuli, and loss of starch grains without early accumulation.

Glasshouse experiments were conducted to determine the effects of trifluralin on root growth and mineral relations of corn seedlings. Root weight to shoot weight ratios of corn seedlings were positively correlated to concentrations of trifluralin in soil. Root length to shoot weight ratios, however, were inversely related to trifluralin concentrations. Phosphorous and potassium concentrations in shoot tissue were reduced 60 and 35%, respectively, by 0.25 mg trifluralin kg−1 soil. Growth inhibition due to trifluralin was partially overcome by supplementing soil with nutrients.

With the advent of herbicides, a new tool has been made available for studying the effect of soil physical properties on crop growth. This new tool may be used for solving such problems as “What are the beneficial effects, if any, accruing from cultivation for the control of weeds?” “Is cultivation necessary for maximum production?”