Control of the annual weed, common groundsel, may be troublesome because of insufficient control by herbicides. Biological control based on stimulating epidemics of the rust fungus Puccinia lagenophorae on common groundsel populations may be an alternative to herbicides if the rust fungus can be integrated with the general use of herbicides against other weeds. Formulations of monolinuron, metoxuron, and pendimethalin were selected for the study. The integration of the rust fungus with each of the three herbicides was evaluated. A three-step procedure was followed to evaluate the integration of the rust fungus and these formulated herbicides. The effect of the selected herbicides on common groundsel was tested in the first step. Only formulated monolinuron completely controlled common groundsel under controlled conditions, indicating that biological control is not required in situations where monolinuron is employed for weed control. The effect of metoxuron and pendimethalin on the rust fungus was tested under controlled conditions in the second step. Formulated metoxuron was not compatible with the rust fungus, indicating that biological control cannot be employed in situations where metoxuron is applied. The effect of pendimethalin on P. lagenophorae epidemics was evaluated using an epidemiological model in the third step. Formulated pendimethalin had no detectable effects on P. lagenophorae epidemics. We concluded that use of P. lagenophorae epidemics for common groundsel control is complementary to application of formulated pendimethalin against other weeds.

Field studies were conducted from 1988 through 1990 in Fayetteville, AR, to measure competitiveness of spotted spurge in cotton. Population levels were established by transplanting seedlings from other field areas. There was a positive linear relationship between cotton boll numbers and seed cotton yield. Percent reduction in cotton height, leaf area, dry weight, boll numbers, and seed cotton yield increased as spotted spurge densities increased. Seed cotton yield reduction was 47, 57, and 85% for spotted spurge densities of 5, 10, and 50 spotted spurge plants m–1 of row.

A biotype of johnsongrass cross resistant to clethodim, sethoxydim, quizalofop-P, and fluazifop-P was identified in several fields in Washington County, MS. Absorption, translocation, and metabolism studies using 14C-clethodim and acetyl-coenzyme A carboxylase (ACCase) activity assays were conducted to determine the resistance mechanism. Absorption of 14C-clethodim was higher in the resistant than the susceptible biotype 4 hours after treatment (HAT), but at 24, 48, and 72 HAT, similar levels of radioactivity were detected in both johnsongrass biotypes. Consequently, resistant plants had more radioactivity present in the treated leaves at 4 and 24 HAT. However, there was no difference between resistant and susceptible biotypes in the translocation of 14C out of the treated leaf at 4, 8, 24, 48, and 72 HAT as a percentage of total absorbed. Metabolism of clethodim was similar in the resistant and susceptible biotypes. There was no difference in the specific activity of ACCase from the susceptible and resistant johnsongrass biotypes (means of 0.221 and 0.223 nmol mg−1 protein min−1, respectively). ACCase from the susceptible biotype was sensitive to clethodim, with an I 50 value of 0.29 μM clethodim. The ACCase enzyme from the resistant biotype was less sensitive, with an I 50 value of 1.32 μM clethodim. The resultant R/S ratio for clethodim was 4.5. These results indicate that resistance to clethodim in this johnsongrass biotype resulted from an altered ACCase enzyme that confers resistance to clethodim.

Five herbicides were applied postemergence to three Louisiana sugarcane (Saccharum officinarum L.) varieties. Nine or 12 lb/A of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) severely injured varieties C.P. 44-101 and C.P. 52-68, but variety N.Co. 310 was not affected. Conversely, N.Co. 310 was injured more by 2,2-dichloropropionic acid (dalapon) than the other varieties. Trichloroacetic acid (TCA) + 2,4-dichlorophenoxyacetic acid (2,4-D) at 10.6 plus 3 lb/A, reduced the yield of variety N.Co. 310 in one of 2 years only. This treatment had no adverse effect on yields of the other two varieties. All varieties appeared tolerant to 2,3,-6-trichlorophenylacetic acid (fenac) applied at 4 to 12 lb/A. Diuron injured a sensitive variety both when the foliage was sprayed and when only the ground at the base of the cane was sprayed. Plants treated in May were injured more than those treated 30 days earlier.

Research on the timing of herbicide application on no-till sorghum [Sorghum bicolor (L.) Moench.] planted into undisturbed winter wheat (Triticum aestivum L.) stubble was conducted at North Platte, NE, during 1980–1982. Applying some herbicides 41 and 25 days prior to planting sorghum maintained weed control, reduced sorghum injury, and increased sorghum yields when compared to application at planting. It was necessary to apply cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} at 2.7 kg ai/ha 41 days prior to planting to avoid sorghum injury. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] + 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 + 0.3 kg/ha reduced grass yields 97, 98, and 99%, while reduction with alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] + 2,4-D at 2.8 + 0.3 kg/ha was 93, 41, and 63%, respectively, when herbicides were applied 0, 25, and 41 days prior to planting.

Protoplasts were isolated from quackgrass to investigate the influence of two surfactants and ammonium sulfate on glyphosate uptake. Without adjuvants, the uptake of glyphosate was not detectable. The uptake of the reference compound 2-aminoisobutyric acid was linear with time and was inhibited 60% in the presence of 10 μM carbonyl cyanide m-chlorophenylhydrazone. Glyphosate uptake increased in the presence of both surfactants and ammonium sulfate. After 0.5 h of incubation the internal glyphosate concentration was 37% of the external concentration (100 μM) in the presence of 0.025 g L−1 Ethomeen T/25, 21% in the presence of 0.25 g L−1 Atplus 201, 13% with 5 mM ammonium sulfate, and 20% with 50 mM ammonium sulfate. The surfactant treatments did not reduce either the viability or the internal pH (= 7.1) as judged by fluorescein diacetate staining or 5,5-dimethyloxazolidine-2,4-dione distribution, respectively. The treatments with ammonium sulfate slightly increased the internal pH. The concentration of Ethomeen T/25 required to disrupt the protoplasts was 0.075 g L−1; Atplus 201 did not disrupt the protoplasts at concentrations up to 10 g L−1.

Two incorporation methods were used in applying eight dinitroaniline herbicides before planting cotton (Gossypium hirsutum L.) for 3 yr. Penoxalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] gave the best stands of cotton. Nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and dinitramine (N4,N4-diethyl-a,a,a-trifluoro-3,5-dinitrotoluene-2,4-diamine) resulted in the poorest stands. In 2 of 3 yr, cotton stands were better where herbicides were incorporated by listing only rather than by disking before listing. The eight herbicides were equally effective in annual grass control when followed by postemergence applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. An-56477 [N,N-bis(2-chloroethyl)-4-methyl-2,6-dinitrobenzenamine] was least effective in controlling annual broadleaf weeds. In 1972, cotton yield was reduced when An-56477 was incorporated by disking. In the average cotton yields for six tests, An-56477 produced significantly lower yields than any other herbicide except butralin [4-(1,1-dimethylethyl-N-(1-methylpropyl)-2,6-dinitrobenzenamine]. No differences in cotton fiber properties or boll components were due to herbicides or method of application.

The abilities of herbicides to either produce superoxide radical or react with this radical were examined. The effect of the herbicides on the superoxide-induced reduction of p-nitro blue tetrazolium chloride was used as an index. Paraquat (1,1-dimethyl-4,4′-bipyridinium ion) enhanced and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] inhibited the reduction of p-nitro blue tetrazolium chloride. Paraquat was reduced photochemically (riboflavin/methionine) or enzymatically (xanthine/xanthine oxidase) and produced superoxide radical upon reoxidation. Diuron and monuron [3-(p-chlorophenyl)-1,1-dimethylurea] interacted with photochemically produced superoxide radical, but not with enzymatically produced superoxide radical. The product of the monuron/superoxide interaction was a demethylated, dechlorinated, water-soluble compound containing phenolic hydroxyl group(s), and was not toxic to oats (Avena sativa L.). The enzyme superoxide dismutase prevented the formation of this product.

From 1962 to 1967, we evaluated herbicides for control of natural infestations of reed canarygrass (Phalaris arundinacea L.) on canal banks of the Huntley, Montana irrigation project. Two,2-dichloropropionic acid (dalapon) and 3-amino-1,2,4-triazole ammonium thiocyanate (hereinafter referred to as amitrole-T) controlled reed canarygrass. These herbicides were compared with a number of others. Spring foliage treatments with a combination of amitrole-T at 2 1b/A and dalapon or trichloroacetic acid (TCA) at 5 or 10 1b/A were more effective than amitrole-T at 4 1b/A. Amitrole-T was more tolerant to fine grasses such as Kentucky bluegrass (Poa pratensis L.) or redtop (Agrostis alba L.) than dalapon and in some situations it was more desirable than dalapon. Dalapon and TCA were more effective as late fall or early winter treatments to control reed canarygrass during the following growing season. Rates of 20 or 40 1b/A controlled the grass for one season even at the water's edge where it is usually more persistent. At 5 to 10 1b/A, 2,3,5-trichloro-4-pyridinol (pyriclor) controlled reed canarygrass, and it also was effective at 2 1b/A with 2 1b/A of amitrole-T.

The metabolism of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] in cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) was investigated using (ring)- 14C 2,4-DB. The herbicide and its 14C-labeled metabolites were isolated from treated cells and medium after 48 h by partition and thin layer chromatography (TLC). The major portion of the radiolabel was in the glycoside fraction (47%) and incorporated into the cell structural material (34%). The remainder of the 14C remained either as the parent herbicide (8%) or an amino acid conjugate of 2,4-DB (10%).

Seeds of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common purslane (Portulaca oleracea L.), fimbristylis [Fimbristylis miliacea (L.) Vahl.], goosegrass [Eleusine indica (L.) Gaertn.], monochoria [Monochoria vaginalis (L.) Presl.], pale smartweed (Polygonum lapathifolium L.), rice flatsedge (Cyperus iria L.), slender amaranth (Amaranthus viridis L.), smallflower umbrella plant (Cyperus difformis L.), and sour paspalum (Paspalum conjugatum Bergius), were placed in nylon mesh bags and buried at 0 (surface), 2.5, 7.5, 15, and 25 cm depths in the soil in November 1974 for 10, 20, 30, 60, 90, 120, 180, 240, 300, and 365 days. They were then recovered from soil to test their germination in petri dishes. Seeds on the soil surface had lower percent germination than those that were buried. Statistical data showed that the total percent germination was not significantly different for the seeds buried at 2.5 cm and deeper in soil when examined at the same burial intervals. During the experiment, the total percent germination of seeds was classified into three groups: (a) percent germination remained constant and relatively high, as for smallflower umbrella plant, common purslane, goosegrass, and slender amaranth; (b) percent germination remained at a plateau for 240 days and then gradually declined at 300 and 365 days, as for sour paspalum; and (c) percent germination was low at the beginning and the end of the experimental period but high in the middle, as for barnyardgrass, monochoria, pale smartweed, rice flatsedge, and fimbristylis. During the experiment, common purslane, barnyardgrass, and monochoria reached a germination peak within the first 5 days. Seeds of the 7 other species germinated within 3 to 5 days or 6 to 10 days, depending on the combination of innate dormancy, temperature, and light intensity.

The relative effectiveness of eight acetanilide herbicides for controlling annual weeds in processing peas (Pisum sativum L.) was evaluated in field studies and the susceptibility of peas to injury from these herbicides was studied in both the field and greenhouse. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was the most phytotoxic to peas grown in washed silica sand in the greenhouse when the herbicides were applied at concentrations of 2 and 8 mg/L. Field trials conducted over a 2-yr period and simulated rainfall experiments in the greenhouse demonstrated that the phytotoxicity to peas by acetanilide herbicides applied preemergence at 2.2 and 4.5 kg/ha was greatly influenced by subsequent rainfall. When 2.5 cm of simulated rainfall were applied immediately after herbicide application, pea injury increased. Injury to peas was avoided in the field by delaying alachlor application at 2.2 kg/ha until peas began to emerge. This treatment also gave excellent control of annual grass weeds. Greenhouse studies demonstrated that injury to peas by all eight acetanilide herbicides at 2.2 and 4.5 kg/ha could be avoided by delaying application until pea emergence. Alachlor, propachlor (2-chloro-N-isopropylacetanilide), and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] gave slightly superior weed control than butachlor [N-(butoxymethyl)diethylacetanilide] and H 22234 [N-chloroacetyl-N-(2,6-diethylphenyl)-glycine ethyl ester].

Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] were evaluated in separate experiments for postemergence control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] and on tolerance of centipedegrass [Eremochloa ophiuroides (Munro) Hack.], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’]. Methazole was also evaluated on tolerance of Kentucky bluegrass (Poa pratensis L. ‘Common’). Metribuzin applied at 0.6 kg/ha and methazole at 1.1 kg/ha as single treatments controlled 82 and 87% goosegrass, respectively. Repeated treatments were needed for similar control of large crabgrass. These treatments did not permanently injure bermudagrass or centipedegrass. St. Augustinegrass was severely injured when treated with single applications of methazole at 1.1 kg/ha or metribuzin at 0.6 kg/ha while Kentucky bluegrass was severely injured by methazole applied at any rate. Methazole caused moderate to severe injury to bermudagrass when applied at 2.2 kg/ha in each of two applications and to centipedegrass when applied at 4.4 kg/ha in each of two applications.

Five herbicides (cloproxydim, fluazifop, haloxyfop, quizalofop, and sethoxydim) were compared from 1984 to 1988 at 250 and 400 g ha−1 for controlling quackgrass within different crop competition and tillage conditions at the Lacombe Research Station. Crop competition usually augmented quackgrass control with the herbicides in conventional-tillage plots although direct statistical comparisons were not made. Without crop competition, haloxyfop and quizalofop at 250 g ha−1 were more effective than the other herbicides in conventional tillage 1 mo after treatment (MAT). In a conventional-tillage situation on a unit active ingredient basis, the herbicides ranked in order of decreasing activity as follows: quizalofop ≥ haloxyfop > fluazifop > cloproxydim > sethoxydim. In a zero-tillage situation, none of the herbicides reduced quackgrass shoot weights by 50% 3 MAT. However, haloxyfop and quizalofop were more effective in suppressing quackgrass shoot weight than the other herbicides in the zero-tillage experiments 3 MAT.

Three annual plant species — erect plantain (Plantago erecta Morris), common chickweed [Stellaria media (L.) Cyrill.], and silver hairgrass (Aira caryophyllea L.)—are commonly found and may dominate a unique flora on areas sprayed with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in cismontane rangelands of California. The basis of this phenomenon is shown to be temperature-related germination requirements, novel seed characteristics, and lack of competition.

Sorption and mobility of 14C-bentazon were evaluated using soil solution and soil-thin-layer chromatography, respectively on three Coastal Plain soils. The proportion of bentazon adsorbed, was pH and concentration dependent and ranged between 28 to 47, 31 to 61, and 17 to 68% for the Dothan loamy sand, Greenville clay, and Troup loamy sand, respectively. Bentazon sorption decreased as soil pH increased from 5.4 to 5.8 on the Troup loamy sand, regardless of bentazon concentration. Sorption of 1 and 10 ppm bentazon decreased as soil pH increased from 5.0 to 5.7 on the Greenville clay and 6.1 to 6.4 on the Dothan loamy sand. Bentazon was least mobile on the Greenville clay and mobility increased as pH increased. Mobility of bentazon was greatest on the Troup loamy sand and was not pH dependent. Bentazon mobility decreased as soil pH increased for the Dothan loamy sand.

Hydroponic treatment with EPTC (S-ethyl dipropylthiocarbamate) inhibited leaf growth and stimulated stem growth of hybrid corn (Zea mays L. ‘Wisconsin 473′). Root treatment with GA3 (gibberellic acid) prevented leaf stunting from EPTC. Most abnormalities in foliar display and height from treatment with 50 μM EPTC were prevented by increasing GA3 levels from 0.5 μM to 10 μM over a week. The effect of EPTC on endogenous gibberellin activity was measured by bioassay of shoot extracts. EPTC (6.7 kg/ha) reduced the levels of total endogenous gibberellin-like substances in eight-day-old seedlings grown in treated soil. Under the environmental condtions of the experiment, this corresponded to the first discernable signs of injury. In addition EPTC induced an abnormal distribution of endogenous gibberellins in the shoots of older corn plants. Leaves of two-week-old EPTC-treated plants contained less gibberellin activity than the leaves of controls. Stems of herbicide-treated plants contained the same levels of gibberellin-like substances as the controls.

Field experiments were conducted at Lincoln, NE, in 1983 and 1984 to determine the effectiveness of subsurface jet injection of herbicides on a simulated shattercane [Sorghum bicolor (L.) Moench # SORVU] infestation in corn (Zea mays L.). Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and EPTC (S-ethyl dipropyl carbamothioate) plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide), incorporated with a disc or applied from the subsurface and surface with a jet injector attached to a sweep plow, generally produced higher corn yields and shattercane control than herbicides applied with the sweep to the subsurface only. EPTC plus dichlormid controlled shattercane better than alachlor. Cultivation improved shattercane control by at least 10% in conjunction with most jet injection and disc-incorporated alachlor treatments. Cultivation increased corn yields by about 10 to 20% when averaged over all herbicides and application patterns. A subsurface plus surface herbicide injection system supplemented with cultivation would be a possible method of incorporating herbicides in reduced tillage to selectively control shattercane in corn.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) required more thorough soil incorporation with a disk, probably to prevent loss by volatility, than did 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). Mechanical incorporation of nitralin could be delayed for 96 hr after application, whereas trifluralin needed to be incorporated within 24 hr to control weeds. Gas chromatographic analyses of soil showed that trifluralin decreased rapidly during the first 24 hr that incorporation was delayed. Application of trifluralin with undiluted crop oil on dry soil did not prolong the persistence prior to incorporation compared to applications with water.

Laboratory assays were conducted to determine the sensitivity of tomato and tobacco cell suspension cultures and tomato and pepper cotyledons to clomazone. A comparison of fresh weight and carotenoid content indicated up to a three-fold difference between the clomazone-tolerant tobacco and clomazone-susceptible tomato cell suspension cultures. In contrast, an approximate 60-fold difference between the tolerant pepper and susceptible tomato cotyledons was observed when total chlorophyll and carotenoid contents were measured. The effect of clomazone and its possible metabolites on in vivo and in vitro extractable IPP isomerase (EC 5.3.3.2) and prenyltransferase (EC 2.5.1.29) activity was investigated. There was no clear inhibitory effect of clomazone or possible clomazone metabolites upon enzyme activity in tomato or tobacco cell suspension cultures or on light or dark grown tomato or pepper cotyledons. No specific enzymatic target site of clomazone was identified in correlation with the reduction in total chlorophyll or carotenoid content.