Safer methods of herbicide application are needed for irregular planting areas. The herbicide 2,6-dichlorobenzonitrile (dichlobenil) was incorporated into various organic mulches so that a specified depth of mulch delivered the desired concentration of herbicide. The incorporation technique provided equal or better weed control than either the dichlobenil or mulch used alone. In addition, prolonged effect of the dichlobenil was realized into the second year when it was incorporated into the mulch. Increasing the mulch depth to 4 inches increased the weed control. A nutrient supplemented mulch in conjunction with the dichlobenil increased the growth of many woody ornamental plants as much as 300 to 400%.

Field research was conducted for 2 yr to determine the effect of reduced rates of glufosinate on growth and yield of non–glufosinate-resistant cotton. Rates of 3.4, 6.7, 13, 26.5, 52.5, and 105 g ha−1, representing 0.008, 0.016, 0.031, 0.063, 0.125, and 0.25 of an effective use rate (420 g ha−1), were applied to cotton at the two-, five-, or nine-node growth stage. Based on analysis of visual injury, cotton response decreased as application timing was delayed in one of the three experiments. Injury response was increased slightly with application at the five- compared with the two-node growth stage and was not significant for the latest application timing (nine-node stage) in two of three experiments. In two of the three experiments, plant height reduction response was lowest at the five-node stage and greatest at the nine-node stage. Regardless of application timing, plant dry weight was negatively affected only with the highest rate of glufosinate. Glufosinate application, based on node above white flower number and percent open boll, did not result in a delay in maturity. Final plant population was reduced in all experiments at the two-node application and in one of the three experiments at the five-node stage. Glufosinate application did not adversely affect final plant population when applied to nine-node cotton. Negative effects on cotton growth were not manifested in seedcotton yield reduction after glufosinate application.

The release of soil-bound 14C-prometryne [N,N′-bis(l-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] residues was affected by soil pH, fertilizer treatments (with or without plants), and the crop species wheat [Triticum aestivum (L.) Merr. ‘Marquis’] and soybean [Glycine max (L.) Merr. ‘Maple Presto’]. More of the bound radioactivity was released following large pH changes in the soil than with small deviations. In addition, more 14C-prometryne was found in the extracts of the soil incubated with large pH alterations. Fertilizing with ionic nitrogen sources (NO3– and NH4+) in the absence of plants was also responsible for releasing higher levels of radioactivity than with the nonionic fertilizer urea. These fertilizer-induced differences in release were not apparent when wheat plants were added to the system. Release of the bound radioactivity, however, was plant specific, particularly in the rhizoplane, since soybean roots elicited a greater release in the rhizoplane than wheat roots. Transport and metabolism of these residues were also plant specific.

In velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), accelerated leaf abscission was a conspicuous response following foliar chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} treatment at 35 g ai/ha. Leaf abscission of treated plants was decreased by AVG [L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid], an inhibitor of endogenous ethylene production. Chlorsulfuron stimulated ethylene production in the abscission zone and leaves of treated plants and also increased cellulase activity in the abscission zone. Accelerated leaf abscission of velvetleaf following chlorsulfuron application appears to result from chlorsulfuron-induced increases in endogenous ethylene production and cellulase activity.

Dalapon (2,2-dichloropropionic acid), TCA ester [ethyleneglycol bis(trichloroacetate)], MSMA (monosodium methanearsonate), and glyphosate [N-(phosphonomethyl)glycine] were evaluated for their effectiveness as spot spray treatments to johnsongrass [Sorghum halepense (L.) Pers.] 30, 75, or 100 cm tall from rhizomes. Glyphosate was also applied as a spot spray to soybeans [Glycine max (L.) Merr. ‘Pickett 71′] to determine its effect on stand losses and subsequent soybean yields. Glyphosate at a concentration of 6 or 12 g/L of water was the most effective treatment regardless of johnsongrass height. A single application provided excellent-to-complete seasonal control within 2 weeks after application. Repeated applications of dalapon, MSMA, and TCA ester would be needed for season-long control. Glyphosate at a concentration of 6 g/L of water applied to 0.5 m long spots of soybeans in late August reduced soybean yields 9, 17, and 28% while the stand was reduced 5,10, and 20%, respectively.

The growth of spiny amaranth and longfruited primrose-willow was studied by growing them alone and in competition with 4 and 12 rice (cv. RC222) plants. Interference with 12 rice plants reduced the height of spiny amaranth beyond 6 wk after planting. The height of longfruited primrose-willow was significantly reduced by the crop interference starting from 4 wk after planting. Both weed species showed the ability to reduce the effects of rice interference by increasing leaf area, leaf and stem biomass in the upper half of the plant, and specific stem length. At 9 wk after planting, for example, longfruited primrose-willow had 89 and 99% leaf biomass in the upper half of the plant when grown with 4 and 12 rice plants compared with only 34% when grown alone. These values for spiny amaranth were 15, 29, and 72% when grown alone, with 4 rice plants, and 12 rice plants, respectively. Despite such plasticity, spiny amaranth's aboveground biomass at final harvest was reduced by 34 and 70% when grown with 4 and 12 rice plants, respectively, compared with its biomass without crop interference. The corresponding values for longfruited primrose-willow were 92 and 98%, respectively. These results suggest that uniform and high crop density could be an important tool to reduce competition from these weeds in direct-seeded rice.

Greenhouse and field studies were conducted with 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron). Tolerant soybean (Glycine max (L.) Merr.) and susceptible tall morningglory (Ipomoea purpurea (L.) Roth.) and ivyleaf morningglory (I. hederacea (L.) Jacq.) were studied with both root and foliar chloroxuron applications. Soybean tolerance to chloroxuron was reduced when treatments occurred in the unifoliate stage; greatest soybean tolerance was noted when soybeans were treated in either the cotyledonary or third trifoliage stage. Tall and ivyleaf morningglory were susceptible to chloroxuron until about 21 days of age (five true leaves), after which resistance increased. Root applications of chloroxuron were more phytotoxic than foliar applications for soybeans and both species of morningglory. In a 3-year study in the field, the following sequential herbicide treatments of either α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 4-(methylsulfonyl-2,6-dinitro-N,N-dipropylaniline (nitralin), S-propyl dipropylthiocarbamte (vernolate), or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) applied preemergence plus chloroxuron postemergence resulted in higher soybean yields than any single herbicide treatment. Weed control was better with the sequential combinations. All sequential combinations with chloroxuron caused soybean injury. Greatest soybean injury occurred when chloroxuron was applied in the first and second trifoliate stage than in the third trifoliate stage. Vernolate alone caused some injury in certain years.

The uptake, distribution, and metabolism of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] by sugarcane (Saccharum officinarum L.) cultivars ‘PR980’ and ‘PR1048’ were determined 3 and 10 days after root treatment with 18.4 μM 14C-ring-labeled diuron. Uptake and distribution did not account for the differential tolerance of the two cultivars to diuron. Concentration of unmetabolized diuron was higher in the shoot and root of susceptible cultivar PR1048 than in tolerant cultivar PR980 at 3 and 10 days after treatment. The predominant metabolic pathway for diuron metabolism in both susceptible and tolerant sugarcane cultivars appeared to be the formation of mono-methyl diuron and its conjugation. The metabolic process was more rapid in PR980 than PR1048, apparently accounting for the tolerance of PR980.

Greenhouse experiments were conducted to determine the persistence of imazapyr and the tolerance of a wide variety of bioassay plants to imazapyr residues in central Texas soils. Eleven bioassay crops were planted in pots 1 d before and 2, 6, and 12 mo after imazapyr application at rates of 0, 0.02, 0.04, 0.07, 0.14, 0.28, 0.56, and 1.12 kg ai ha−1. Imazapyr was phytotoxic 12 mo after treatment to all crop plants in at least one rate. Forage grasses and herbs were highly susceptible to imazapyr residual carryover damage, as was corn and cabbage. Bean and squash were tolerant of imazapyr residues. No statistical differences occurred in imazapyr phytotoxicity to corn grown in leached vs. nonleached pots.

Six herbicides were evaluated at two rates on sweet potatoes [Ipomoea batatas (L.) Lam. ‘Georgia Red’, ‘Georgia Jet’] with and without cultivation from 1972 through 1976. Cultivation with a ground-driven rotary hoe about 2 weeks later improved the control of late-season broadleaf weeds such as Florida beggarweed [Desmodium tortuosum (Sw.) DC] and showy crotalaria (Crotalaria spectabilis Roth.). Cultivation improved weed control where vernolate (S-propyl dipropylthiocarbamate), DCPA (dimethyl tetrachloroterephthalate), and napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] were applied. The improved weed control in cultivated treatments resulted in increased sweet potato yields in 1972 and 1973, which also were the years with the highest weed populations.

Preplanting application of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), reduced the number of monosodium methanearsonate (MSMA) applications needed for the control of johnsongrass (Sorghum halepense (L.) Pers.). The combined effect enabled weed control to be completed before cotton (Gossypium hirsutum L.) began to bloom, and hence without causing damage to the crop.

Three selections of johnsongrass (Sorghum halepense (L.) Pers.) were collected from three locations and designated as the N, NS, and S selections, respectively. The selections were studied for growth differences and for a differential response to dalapon (2,2-dichloropropionic acid). The N selection control plants flowered 2 weeks earlier than the other selections. The S selection yielded significantly greater root, rhizome, and total fresh weight than the NS and N selections. The N selection exhibited the most susceptibility to dalapon by producing the shortest plants, the least stem and leaf numbers, and the lowest shoot, root, rhizome, and total fresh weight of the three selections.

Honey mesquite [Prosopis julifiora var. glandulosa (Torr.) Cockerell] and velvet mesquite [P. julifiora var. velutina (Woot.) Sarg.] seedlings were treated on individual leaves with 20 or 40 μg of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), or a 1:1 mixture thereof. Formulation of herbicides in a DMSO-complex carrier (dimethyl sulfoxide, ethylene glycol, phytobland oil, water: 50:25:15:10, v/v) enhanced activity considerably over that obtained with an aqueous carrier, the degree of enhancement being greater with 2,4,5-T than with picloram. Lack of major varietal differences in morphological or anatomical response suggests that observed varietal differences in sensitivity of field mesquite to aerial sprays are not a function of the variety itself, but are related to climatic or edaphic differences among sites which the varieties occupy.

Growth chamber experiments were conducted to elucidate the morphological and physiological responses of rice to postemergence application of fenoxaprop. Two rice cultivars, ‘Newbonnet’ and ‘Mars’, and barnyardgrass were treated with 0.17 kg ai ha−1 fenoxaprop at the five-leaf stage. Within 2 days of fenoxaprop application, rice cultivars developed a white chlorotic band across leaves that were in direct contact with spray droplets. Leaf elongation rates for the two rice cultivars were inhibited by 40% after 4 days and by over 50% after 14 days. Inhibition of leaf elongation by fenoxaprop contributed to an overall decrease in leaf area and shoot dry weight. Net photosynthesis was reduced by 35% in fenoxaprop-treated plants 11 days after application, although stomatal conductance was not affected. Nitrogen fertilization prior to fenoxaprop application increased foliar injury of both rice cultivars. Visible injury symptoms showed the following order of susceptibility to foliar-applied fenoxaprop: barnyardgrass > Mars rice > Newbonnet rice.

Four Centaurea species, diffuse knapweed (C. diffusa Lam. # CENDI, spotted knapweed (C. maculosa Lam. # CENMA), yellow starthistle (C. solstitatilis L. # CENSO), and the closely related Russian knapweed [Acroptilon repens (L.) DC. syn. Centaurea repens L. # CENRE] are serious introduced weeds which infest extensive areas of pasture and rangeland in Canada and the United States (1, 10, 14, 17, 18, 26, 30). Russian knapweed and yellow starthistle are also troublesome in cultivated land (1, 14, 26). These four species are members of the Cardueae tribe of the Asteraceae family and have been accidentally introduced from Eurasia as contaminants in crop seed.

Wild poinsettia control in peanut was evaluated following various preplant-incorporated and postemergence herbicide applications. The addition of vernolate or alachlor to a preplant-incorporated treatment of benefin improved wild poinsettia control obtained with treatments of lactofen or paraquat plus alachlor applied at the time of peanut emergence. Lactofen applied postemergence following lactofen plus alachlor applied at the time of peanut emergence provided ≥92% wild poinsettia control and peanut yields equivalent to the handweeded control. Treatments of paraquat plus alachlor applied at the time of peanut emergence followed by acifluorfen (applied once or twice) or paraquat followed by acifluorfen provided good (74 to 100%) wild poinsettia control for up to 12 weeks after planting and peanut yields not different from the handweeded plots. Treatments that did not provide at least 92% wild poinsettia control when evaluated 5 weeks after planting resulted in significant peanut yield reduction compared to the handweeded control.

Investigations were conducted to determine whether light, temperature, or their interaction stimulated primary basal-bulb formation on underground stems of yellow nutsedge (Cyperus esculentus L.) seedlings grown from tubers. Basal-bulb formation results when internodes shorten and leaves lengthen. When seedlings were grown without medium around the underground shoots, a temperature alternation of 10C stimulated basal-bulb formation; light did not affect the process. When seedlings were grown with medium around the underground shoots, either light or alternating temperature stimulated basal-bulb formation. Nine colors of light gave the same stimulus as white (fluorescent) light. Phytochrome did not appear to be the photoreceptor for the stimulus, as both red and far-red light responses were identical to that of white light.

Napropamide [2 - (α - naphthoxy) -N,N- diethylpropionamide] influx was studied using excised root segments of corn (Zea mays L.). An initial rapid influx was followed by a slower, steady influx rate. Total influx was separated into a component that eluted from the tissue (exchangeable fraction) and a nonexchangeable fraction (residual fraction). After 5 min the residual fraction was responsible for the continued influx. In further studies with root segments this fraction was nonsaturating, increased with increased temperature, and was reduced by anaerobic conditions. The exchangeable fraction was controlled by diffusional processes. The overall influx process was attributed to an initial passive diffusion supplemented with time by a binding of napropamide into the residual fraction.

An experiment was established at three sites to determine the longevity and distribution of rhizome buds of two quackgrass biotypes in the soil profile under two tillage systems (no-till or fall-plow). The experiments were established in May 1987 at sites initially free of quackgrass. Rhizome segments with three nodes were planted 2 to 5 cm deep to give an initial density of 21 buds m-2. Production of new buds was prevented in subsequent years. Rhizome bud populations were sampled every 6 mo between October 1987 and October 1989. Buds were produced until snow cover, indicating the need to control quackgrass until late fall to prevent a bud population increase. Under no-till conditions, 94% of quackgrass buds occurred in the top 10 cm of soil while 68 and 19% were found below 10 and 20 cm, respectively, in the fall-plow treatments. A control program against quackgrass should aim at keeping the majority of rhizomes in the top 10 cm in order to facilitate control by having most shoots emerging at the same time. There was no statistically significant difference in bud longevity between biotypes, sites, and tillage systems. Viability of the rhizome buds declined rapidly during the first year. In most cases it took 2 yr for the bud populations to reach extinction although 0.6% of buds of one biotype survived as long as 30 mo in one of the three sites. Therefore, a minimum of 2 yr of total control would be required to eradicate quackgrass from most locations.

The phytotoxicity of the butyl ester of fluazifop to quackgrass was enhanced by the addition of a nonionic surfactant and an oil additive either alone or in mixture to the spray solution. The enhancement caused by the surfactant was consistently greater than that caused by the oil additive. A higher level of quackgrass control was achieved at the carrier volumes of 100, 200, or 400 L/ha, than at 800 L/ha. Quackgrass growth inhibition was greater following application of small herbicide droplets which averaged 0.25 μl compared to larger herbicide droplets at each herbicide application rate. When droplet concentration was varied and different doses of the herbicides applied to plants, no significant differences were noted at the highest dose. However, at intermediate dose treatments, the least concentrated droplets (2.5 μg/μl) were most phytotoxic. Herbicide droplets placed at basal areas of leaves were more phytotoxic than when placed at lamina apices and middle areas. This effect was most pronounced on adaxial rather than abaxial surfaces. In general, application of droplets to younger leaves resulted in greater phytotoxicity than treatment of older leaves.