The fate of foliarly applied 14C diclofop-methyl {methyl 2-[4-(2,3-dichlorophenoxy)phenoxy] propanoate} was determined in intact plants of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], a susceptible (S) grass; proso millet (Panicum miliaceum L.), a moderately susceptible (MS) grass; longspine sandbur [Cenchrus longispinus (Hack.) Fern.], a tolerant (T) grass; soybean [Glycine max (L.) Merr. ‘Hark’], and cucumber (Cucumis sativus L. ‘Green Star’), both T broadleaf plants, 1,3, and 5 days after treatment (DAT). Diclofop-methyl accounted for 94% of the radioactivity washed from the leaf surfaces of all species. Plant extracts contained diclofop-methyl, diclofop, and water-soluble conjugates. Barnyardgrass (S), proso millet (MS), and soybean (T) had 75, 68, and 66% of the extracted radioactivity as diclofop and diclofop-methyl. Longspine sandbur (T) and cucumber (T) had 71 and 84% of the extracted radioactivity as water-soluble conjugates. Acid hydrolysis of the water-soluble conjugates yielded 84 and 71% diclofop in barnyardgrass (S) and proso millet (MS). Cucumber (T), soybean (T), and longspine sandbur (T) had 43, 23, and 25% ring-OH diclofop. Alkaline hydrolysis of the non-extracted plant residue yielded diclofop as the major component in all species.

Preplant-incorporated applications of commercial formulations of EPTC (S-ethyl dipropylthiocarbamate) and butylate (S-ethyl diisobutylthiocarbamate) plus the herbicide antidote R-25788 (N,N-diallyl-2,2-dichloroacetamide) were evaluated for their interactions with preemergence applications of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in corn (Zea mays L., ‘Pioneer 3780’) under greenhouse conditions. The thiocarbamate herbicides plus the antidote were used at 1.1, 2.2, 3.4, and 4.5 kg/ha, and they were evaluated against 0.3, 0.6, and 1.1 kg/ha of tebuthiuron. Shoot dry weight and shoot height of corn seedlings were measured at 24 days after treatment. Growth responses of corn to combination treatments of these herbicides were significantly reduced. Statistical analysis of the data showed that tebuthiuron interacted synergistically with both EPTC and butylate in the presence of the herbicide-antidote R-25788.

Salt rabbitbrush [Chrysothamnus nauseosus (Pallas) Britt., ssp. consimilis (Greene)] and greasewood [Sarcobatus vermiculatus (Hook.) Torr.] grow slowly in early spring until mid to late May. They then begin a period of rapid growth, at which time susceptibility to foliar herbicides is probably greatest. Greasewood ceases rapid growth in mid June to early July, but salt rabbitbrush continues to grow rapidly until early August. Greasewood that resprouts after herbicide application has a longer rapid-growth period than shrubs in an untreated stand. An average leader length of 4 cm indicates that rapid growth of salt rabbitbrush is underway, and first opening of the flower buds indicates that rapid growth is over. Appearance of greasewood staminate spikes indicates that rapid growth has begun, and the first appearance of dried spikes indicates that growth has ceased. Simultaneous control of these shrubs with a single application of phenoxy herbicides may only be possible during the relatively short period when both are growing rapidly. This period may only occur from late May to mid June in some stands and years, but may occur from mid May to early July in other cases.

In a 2-yr field study with preplanting-soil-incorporated treatments of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], tolerance of soybeans [Glycine max (L.) Merr.] to these herbicides, as measured by seed yield, was increased by increasing the seeding rate one-and-one-half or two times that normally recommended. These results agree with suggestions in the literature that plants can compete for herbicide in the soil, and suggest that increased seeding rates of soybeans can partially reduce the adverse effects of atrazine carryover or excessive metribuzin application.

Applications of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] at rates from 0.3 to 1.4 kg/ha were made in the field to soils of 2 and 30% (w/w) soil moisture. After 2 to 4 days, all soils were irrigated to establish stands of either sweet corn (Zea mays L. ‘Jubilee’) or winter wheat (Triticum aestivum L. ‘Stephens’) used as bioassay species for ethofumesate activity. Ethofumesate, at most rates, was significantly less effective on both corn and wheat when applied to dry soil than to wet soil. In greenhouse studies, ethofumesate activity was significantly greater when incorporated into soil of 12% than 2% (w/w) moisture 2 or 4 days prior to irrigation. An increase in herbicide activity was apparent as the length of time between herbicide application and wetting increased from 2 to 4 days. Analysis of wet (20%, w/w) and dry (2%, w/w) soils treated with equal levels of ethofumesate revealed no loss of herbicide applied to wet soil over a 12-day period, but in the dry soil, the amount extracted after 12 days was 10% of the amount extracted at 0 days. These data and other considerations suggest that chemical degradation of ethofumesate is the most likely mechanism for the activity loss in dry soil.

Three field studies were conducted over a 2-yr period to evaluate the persistence of fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl) aniline], and to determine whether DBCP (1,2-dibromo-3-chloropropane) affected persistence. Fluchloralin was applied to field plots at 1.1 kg/ha with and without DBCP at 20.5 kg/ha. In the first study, soil samples were taken periodically over a 1-yr period and assayed for fluchloralin by both gas chromatography (GC) and a sorghum (Sorghum bicolor L. Moench ‘AKS-516’) root-elongation bioassay. Both methods of analysis indicated that fluchloralin persistence was unaffected by DBCP. An oat (Avena sativa L. ‘Ora’) bioassay of soil from the field plots 41 weeks after treatment showed no residual herbicide activity. In the next two field studies, soil samples were taken periodically over a 32-week period and assayed by GC for fluchloralin. A greenhouse sorghum bioassay of soil samples taken from both tests 32 weeks after application showed residual activity of fluchloralin in one test, but differences were not attributable to DBCP. A two-phase process of fluchloralin dissipation in field soil was indicated from analysis of the data using a complex first-order regression, as opposed to a simple first-order regression. Half-life values describing fluchloralin persistence, using the complex first-order regression, ranged from 2.3 to 3.7 weeks for the first phase and 9.5 to 26.7 weeks for the second phase.

Mechanical scarification of burcucumber (Sicyos angulatus L.) seeds resulted in increased water absorption and germination. Burcucumber germination occurred at temperatures ranging from 15 to 35 C with optimum germination occurring from 20 to 30 C. Scarified burcucumber seeds were more sensitive to simulated moisture stress than were either soybean [Glycine max (L.) Merr. ‘Williams’] or corn [Zea mays L. ‘Pioneer Brand 3369A’]. Regardless of osmotic potential, intact burcucumber seeds did not germinate; scarified seeds germinated at osmotic potentials to −6 bars. Cold stratification at 4 C for 18 weeks modified seedcoat permeability so that 11% of non-scarified burcucumber seeds germinated. Increasing depth of planting decreased emergence with limited emergence occurring at depths of 15 and 16 cm in field and growth chamber studies, respectively.

Growth chamber studies and field trials were conducted to evaluate the toxicity of glyphosate [N-(phosphonomethyl)glycine] and certain other herbicides to wild garlic (Allium vineale L.). Toxicity to wild garlic increased with increasing rates up to 6 kg/ha. Glyphosate was more toxic to wild garlic when applied in spray volumes of 125 to 500 L/ha than in greater volumes. Addition of surfactant did not increase toxicity or absorption rates of 3 kg/ha of glyphosate, but did increase the advantage of 2 kg/ha of glyphosate over 2,4-D [(2,4-dichlorophenoxy)acetic acid]. When glyphosate was sprayed on wild garlic plants at 3 kg/ha, then washed off after 2, 4, 8, 16, and 32 h, absorption of a biologically significant amount of glyphosate required 8 h, and toxicity increased through the 32-h exposure. Injury, which increased as mowing was delayed up to 12 days after application, indicated that significant quantities of glyphosate were translocated between 3 to 12 days after treatment in a field test. Glyphosate; 2,4-D; 2,4-D + mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} + dicamba (3,6-dichloro-o-anisic acid); and VEL-4207 [N-phenyldiethanolamine-bis-(2-methoxy-3,6-dichlorobenzoate)], applied in a sequence of either spring-fall-spring or fall-spring, were compared for wild garlic control. All herbicides tested controlled wild garlic, but glyphosate was more effective than 2,4-D after spring-fall-spring applications. All spring-fall-spring treatments except 2,4-D + mecoprop + dicamba significantly reduced the number and weight of hardshell bulbs present 8 weeks after the last treatment. The initial treatment in the spring-fall-spring sequence was necessary to reduce hardshell bulb populations the second spring. One year after treatment wild garlic reinfested all plots.

Absorption and translocation of 14C-metriflufen {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} in johnsongrass [Sorghum halepense (L.) Pers.] and soybean [Glycine max (L.) Merr. ‘Lee 68’] were evaluated under different environmental conditions. At 40% relative humidity (RH), an increase in air temperature from 18 to 35 C increased translocation of the 14C in johnsongrass more than four-fold following application of 14C-metriflufen to an area on the third leaf. At 100% RH, translocation of the 14C was twice as great at 27 C as at 18 C, but translocation at 35 C was intermediate. In the combined analysis, translocation in johnsongrass was no better at 100% RH than at 40% RH. Regardless of level of RH, most translocation in johnsongrass at 18 and 27 C was toward the distal half of the treated leaf, but at 35 C most translocation was toward the proximal half of the treated leaf. Translocation of 14C in soybeans increased more than four-fold as air temperature was increased from 18 C to 35 C, and more translocation occurred at 100% RH than at 40% RH at 18, 27, and 35 C. More than 80% of the 14C-metriflufen remained in the treated leaf or on the surface of treated soybean leaves 48 h after application. More of the applied radioactivity was recovered from soybean plants than from johnsongrass plants.

Field studies were conducted at Florence and Clemson, South Carolina to measure the influence of soybean [Glycine max (L.) Merr.] planting dates on the length of early-season weed control needed to prevent yield reductions, the rate of shade development, and suppression of annual weeds by soybeans. The rate of shade development was similar for both planting dates during the 9- to 11-week period after planting for Florence and Clemson, respectively. The period of weed-free maintenance required to prevent soybean yield reductions was not affected by planting dates. With cultivation between rows, early- and late-planted soybeans required 3 weeks of weed-free maintenance to achieve maximum yields. Lower weed weights resulted from late than early soybean plantings. At Clemson, 3 weeks of weed-free maintenance for early and late plantings reduced weed weights 97 and 91%, respectively. Weed weights at Florence were reduced 85% with 3 weeks of weed-free maintenance for the late plantings, whereas 5 weeks were required to reduce weed weights 88% for early plantings.

Six species of 2- or 3-yr-old woody nursery stock were planted in the field in May 1976. Glyphosate [N-(phosphonomethyl) glycine] at 2.2 or 4.5 kg/ha or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 0.6 or 1.1 kg/ha were applied one or two times as directed sprays in 1976 and one, two, or three times each season in 1977 and 1978. Three applications of glyphosate or paraquat were required to control weeds during the entire growing season. When late-season applications of glyphosate were made during 1977, residual weed control was observed during early 1978. When glyphosate was applied twice a year for 3 yr at 4.5 kg/ha, four of the previously dominant perennial weeds were controlled, including common dandelion (Taraxacum officinale Weber), broadleaf dock (Rumex obtusifolius L.), buckhorn plantain (Plantago lanceolata L.), and red sorrel (Rumex acetosella L.). Three applications provided 100% control of seven of the eight remaining broadleaf perennials, including hedge bindweed (Convolvulus sepium L.) and Canada thistle [Cirsium arvense (L.) Scop.]; six of seven species of broadleaf annuals, including Pennsylvania smartweed (Polygonum pensylvanicum L.) and tumble pigweed (Amaranthus albus L.); and all of the remaining grass weeds. Crop size, crop quality, and marketability of the six ornamental species were not adversely affected by either herbicide. Two or three applications of glyphosate at 2.2 kg/ha or two treatments at 4.5 kg/ha increased plant size of andorra junipers (Juniperus horizontalis Rend.). Three treatments of glyphosate at 2.2 kg/ha also increased the size of dwarf Japanese yews (Taxus cuspidata Sieb. & Zucc.) and two treatments at 4.5 kg/ha increased the size of boxleaf Japanese holly (Ilex crenata Thunb.).

The influence of common ragweed (Ambrosia artemisiifolia L.) interference on soybean [Glycine max (L.) Merr. ‘Ransom’] yield was studied in the field utilizing naturally occurring weed populations. The damage-threshold population for a full-season, in-row common ragweed infestation was four weeds/10 m of row, which resulted in an 8% yield loss. Soybeans kept weed-free for 2 weeks or longer after emergence in a dry year produced normal yields, but 4 weeks of weed-free maintenance was required when adequate moisture was available early in the growing season. Soybean yield was not reduced by a natural population of common ragweed if the period of interference was limited to 6 weeks or less after crop emergence. By 8 weeks after emergence, common ragweed height averaged 25 cm taller than soybeans, and the weed canopy intercepted 24% of the photosynthetically active radiation.

A method is described for the large-scale production of a granular formulation of Alternaria macrospora Zimm. The granular preparation consisted of spores, mycelia, and vermiculite. This formulation of A. macrospora, applied preemergence or postemergence, controlled spurred anoda (Anoda cristata Schlecht.) plants in greenhouse and field tests. The pathogen did not significantly affect emergence or dry weight production of cotton (Gossypium hirsutum L. ‘Stoneville 213’) seedlings. The fungicides PCNB (pentachloronitrobenzene) and ETMT [5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole] did not significantly affect spurred anoda control with A. macrospora. The method for production and formulation of A. macrospora was modified to produce spores and granular formulations of other Fungi Imperfecti: Drechslera sp. and Fusarium spp. (Moniliales), Colletotrichum spp. (Melanconiales), and Phyllosticta sp. (Sphaeropsidales).

Fall-applied herbicides were evaluated in field studies conducted in 1978 through 1980 in western Nebraska for selective weed control in nonirrigated, established alfalfa (Medicago sativa L. ‘Ranger’). All herbicides effectively controlled downy brome (Bromus tectorum L.). Broadleaf weeds were differentially controlled by the herbicides tested. All herbicide treatments increased forage production and protein content over that produced in the untreated check. Increasing the rate of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] above amounts needed for effective weed control caused an increase in the protein content of alfalfa forage above that resulting from normal use rates.

In field and greenhouse studies, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was found to antagonize buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} injury to corn (Zea mays L.) when both herbicides were preplant incorporated. Similar results were found with five of seven other acetanilide herbicides tested. The antagonism between buthidazole and alachlor also occurred with common cocklebur (Xanthium pensylvanicum Wallr.) and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.] but not with five other weed species. Preplant-incorporated applications of alachlor had little to no effect on the response of corn to postemergence applications of buthidazole, but alachlor increased the susceptibility of ivyleaf morningglory to postemergence applications of buthidazole. No antagonism was observed when alachlor was included in postemergence applications of buthidazole to corn or ivyleaf morningglory.

An electrical discharge system (EDS) was evaluated in field studies conducted in 1977 through 1979 in western Nebraska for its ability to control weed escapes in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′). Nine weeks after sugarbeets were planted, kochia [Kochia scoparia (L.) Schrad.] had attained a height above sugarbeets sufficient for EDS treatment. Redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.) generally attained sufficient height above sugarbeets 11 and 13 weeks after sugarbeet planting. Sugarbeet root yields were reduced 40, 20, and 10% from competition by kochia, common lambsquarters, and redroot pigweed, respectively. Treatment of kochia, redroot pigweed, and common lambsquarters with EDS in some cases resulted in a reduction in weed height. The EDS treatments reduced the stand of all weeds 32, 39, and 47% for 1977, 1978, and 1979, respectively. Although the EDS treatments failed to kill many weeds, it did suppress the competitive ability of the three weeds to the extent that sugarbeet yields were higher in areas receiving EDS treatments than areas receiving no EDS treatment.

The effect of 1.0 ppmw fluridone {1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1H)-pyridinone} on growth of American pondweed (Potamogeton nodosus Poir.) and sago pondweed (Potamogeton pectinatus L.) was examined in plants kept in darkness or under various numbers of 12-h photoperiods. When plants were exposed to 1.0 ppmw fluridone for 1 to 10 12-h days, no stunting of American pondweed occurred until 21 days after treatment. Thirtythree days after treatment, plants that had received 4 to 10 days' exposure were most stunted. Sago pondweed was slightly more susceptible than American pondweed (87% and 50% reduction in length, respectively) 37 days after a 10-day exposure. Chlorophylls a and b were significantly lower in both species 14 days after all fluridone treatments. American pondweed plants exposed to fluridone continuously (1.0 ppmw) for 15 days, but given 0, 3, 6, 9, 12, or 15 12-h days were stunted only after having received at least six photoperiods. Stunting in sago pondweed was only slightly light-dependent. Neither species absorbed significantly more 14C-labeled fluridone after 2, 4, or 14 photoperiods compared to plants kept in darkness for the same time.