A soil sampler was constructed to collect soil cores in plastic tubes to a depth of 30 cm. This method of sampling prevents loss of soil, minimizes soil contamination, and permits proportional sectioning of the soil core into desirable segments for bioassay or chemical analysis.

Soil carryover of the herbicide trifluralin can injure Zea mays. Therefore, the development of resistant hybrids can be an important breeding objective. This research was conducted to study the genetic variability for trifluralin resistance in Z. mays, the effects of genes controlling resistance, and the seed lipid content of resistant (R) and susceptible (S) inbreds. Twenty inbreds were tested under greenhouse conditions at three trifluralin rates (0, 12.5, and 125 g ai ha−1). Lo1067 was the most resistant, and A632 was the most susceptible inbred. Hybrids among R and S inbreds were tested, along with their parents, under greenhouse conditions (using the same three rates) and in the field (at 0, 0.4, and 0.8 kg ai ha−1). Under both greenhouse and field conditions, inbreds R were more resistant than S. Hybrids R × R were more resistant than S × S, indicating that additive effects were important. Hybrids R × S and S × R did not significantly differ, indicating that reciprocal effects were not important. On average, hybrids R × S and S × R were intermediate between R × R and S × S, suggesting that nonadditive effects were negligible. The difference between the mean across hybrids and the mean across parents (further estimating the importance of nonadditive effects) was significant only for parameters investigated in the greenhouse. Greenhouse data were correlated with field data, but the coefficients of determination were < 50%. The ability to predict hybrid resistance on the basis of parental mean was higher in the greenhouse (r 2 = 0.78) than in the field (r 2 = 0.47). R and S inbreds also differed in seed lipid content, but correlations were negligible with greenhouse and field data. Data indicated the presence of genetic variability for trifluralin resistance, that additive effects were prevailing, and that the resistance level was not related to seed lipid content.

The metabolism of 14C-SAN-6706 [4-chloro-5-(dimethylamino)-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone] and 14C-norflurazon [4-chloro-5-(methylamino)-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone] were studied in cranberry plants (Vaccinium macrocarpon Ait. ‘Early Black’) for a 36-day period. Both compounds were readily translocated with progressively more label being present in the shoot portion with time. The two compounds are demethylated to the desmethyl analogue SAN-9774 (4-chloro-5-amino-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone). Berry samples from cuttings contained no detectable radioactivity while samples from 2 year-old cranberry plants contained 20 ppb or less.

Akinetes (spores) of the green, filamentous alga Pithophora oedogonia (Montagne) Wittrock were more copper resistant than filamentous cells, tolerating copper concentrations as high as 4 μg·ml-1 (16 μg·ml-1 copper sulfate pentahydrate). The localization of copper in viable and nonviable cells was conducted using cell fractionation and cytochemical/ultrastructural methods. In copper-exposed viable akinetes, copper was bound primarily to the outer layers of the cell wall. In nonviable cells, copper was found randomly distributed throughout the cytoplasmic and vacuolar regions. No evidence for compartmentation of copper as vacuolar or intranuclear deposits was demonstrated. Copper uptake into the cell wall was associated with release of equimolar amounts of calcium, magnesium, and zinc. When viable copper-treated akinetes were allowed to recover in copper-free medium, the copper was gradually released from the cell wall, presumably to the culture medium. A portion of the copper also appeared to be redistributed to new cell wall material during the akinete germination process. The differential tolerance of P. oedogonia akinetes to copper in comparison to filamentous cells appears to be due to a combination of factors that include cell surface/volume ratios, metabolic activity, and cell wall copper-binding components.

Research was conducted to determine foliar absorption of 14C-clethodim and its polar degradation products with five adjuvants and to compare the relative herbicidal activity of clethodim and its polar degradation products. Differential 14C-clethodim and 14C-polar degradation products absorption occurred among the five adjuvants. Adjuvants that mediated rapid foliar absorption of clethodim did not always mediate rapid foliar uptake of polar degradation products. Herbicidal activity of clethodim exceeded activity of polar degradation products regardless of time of day of application or whether adjuvant was used. Inclusion of adjuvant was required for herbicidal activity of polar degradation products. Clethodim activity declined when applied at 0800 h EDT compared to applications at 2000 h EDT. To maximize herbicidal activity of clethodim, adjuvants should be selected that mediate rapid foliar absorption of both clethodim and the polar degradation products of clethodim and that minimize photodegradation of clethodim.

Studies were conducted to determine the tolerance of several crops to herbicide sprays containing three spray drift control adjuvants, a cross-linked polyacrylate (Norbak), a pseudo-plastic spray gel agent composed primarily of natural carbohydrates (Dacagin), and hydroxyethylcellulose (Vistik). Other studies were conducted to observe the effect of the adjuvants on the efficacy of 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) when used with or without a surfactant, the effectiveness of the adjuvants in preventing 3-amino-s-triazole plus ammonium thiocyanate (amitrole-T) from being washed off plants, and the effect of the adjuvants in reducing vapor loss of the ethyl ester of (2,4-dichlorophenoxy) acetic acid (2,4-D) from leaves. Little increased injury was caused from the addition of the adjuvants to herbicides sprayed on several crops. The adjuvants added to paraquat were not effective substitutes for surfactant; however, Dacagin or Vistik added to paraquat combined with surfactant did not reduce the efficacy of paraquat. Norbak reduced the efficacy of paraquat, with or without the addition of surfactant. The adjuvants did not prevent amitrole-T from being washed off plants. Results of vapor studies suggested that Dacagin and Norbak reduced vapor loss of the ethyl ester of 2,4-D from plant surfaces.

Spring establishment of tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31’) is preferred over fall for turfs in Nebraska. Siduron [1-(2-methylcyclohexyl)-3-phenylurea] is commonly used for weed control in spring-seeded tall fescue. Siduron application rates of 6.8, 13.6, 27.2, and 40.8 kg/ha were compared with an untreated control in this study. All siduron applications reduced stand development. The 6.8 kg/ha rate nearly doubled the number of days for seedling emergence. Abnormal seedlings increased with increasing application rates and percent germination decreased with increasing rates. Tiller number declined at rates of 13.6 kg/ha and above. Plants treated with 6.8 kg/ha were 1.3 cm shorter than those growing in the untreated control. Plant and root dry matter production decreased with increasing application rates. Root weight was reduced more than plant weight. Degree of wilting and drought injury increased at 13.6 kg/ha. Water use declined with increased siduron application rates. The amount of water lost before wilting occurred also declined as siduron application rates increased. High temperature injury on seedlings was reduced with increasing rates of siduron. Reduction in high temperature injury was significantly correlated (r = 0.98) to reduced plant tissue moisture.

The time-dependent uptake, translocation, and metabolism of [14C]MG-191 safener and the influence of EPTC on these processes were studied using 5-d-old corn seedlings grown in nutrient solution. Plants absorbed relatively low levels of root-applied radiolabel at both 10 μM and 50 μM [14C]MG-191 rates during 6 d of exposure. Amounts of absorbed radioactivity increased with time. Addition of 50 μM EPTC, in general, did not alter amounts of [14C]MG-191 taken up. Initial translocation of radiolabel from roots to shoots was more rapid at 10 μM [14C]MG-191 treatment compared to 50 μM. EPTC had no effect on radiolabel movement at either safener rate. MG-191 was metabolized rapidly to water-soluble metabolites. Slower formation of water-soluble products was detected only during the initial 3 h in the presence of EPTC. Also, thin-layer chromatographic analyses of water- and hexane-soluble metabolite fractions confirmed rapid transformation of the parent molecule. Because addition of EPTC retarded parent MG-191 metabolism 3 h after treatment, we assume that initial availability of the MG-191 molecule may be prerequisite to its protective effect.

Two formulations of triallate [S-(2, 3, 3-trichloroallyl)diisopropylthiocarbamate] were evaluated for their effectiveness in controlling wild oat (Avena fatua L.) in spring wheat (Triticum aestivum L.) in 12 field experiments conducted between 1967 and 1978. Control of wild oat was greater with fall applications of triallate granules than liquid or with spring applications of either liquid or granules. Further-more, 1.1 kg/ha of triallate granules applied in the fall controlled wild oat as well as did 1.7 kg/ha of liquid triallate applied in the fall. Wild oat control with triallate was usually better when soil incorporated than when surface applied regardless of formulation or time of application. Triallate granules controlled wild oat similarly on either plowed ground or wheat stubble; whereas, liquid triallate controlled wild oat better on plowed ground than wheat stubble. A delay of 8 h in triallate incorporation did not reduce wild oat control with either formulation; however, a delay of 24 h reduced wild oat control with the liquid formulation.

Kyllinga species are becoming more prevalent in turfgrass sites throughout North America. The effects of nitrate (50, 200, and 400 mg L−1), temperature (33/24, 25/17, 19/11 C day/night, respectively), and light on seed germination of three Kyllinga species were investigated in growth chambers. Nitrate concentrations did not stimulate Kyllinga species seed germination compared with untreated seeds. All Kyllinga species seeds failed to germinate in darkness but resumed germination once they were placed in light. This is an important pest management strategy because a dense, uniform turfgrass stand with its minimum light penetration to the soil would minimize Kyllinga species seed germination. Higher temperatures increased seed germination rate and percentage of each species after 8 wk. Maximal (> 90%) K. brevifolia germination occurred 2 to 4 wk after initiation in every seed study, whereas K. squamulata seeds germinated continuously. Minimal (< 10%) K. pumila seeds germinated until alternating diurnal temperatures were imposed.

Roots of susceptible cucumber (Cucumis sativus L. ‘Chicago pickling’) and tolerant wheat (Triticum aestivum L. ‘Manitou’) seedlings were treated with 3,6-dichloro-o-anisic acid (dicamba) or (2,4-dichlorophenoxy)acetic acid (2,4-D) for either 10 or 46 hr. The roots were excised and nucleohistones were isolated and fractionated by polyacrylamide gel electrophoresis. In untreated cucumber roots there were four major nucleohistone fractions. Two of these fractions decreased or were not detectable 10 or 46 hr after treatment with dicamba or 2,4-D. In wheat, the nucleohistone fractions of the treated roots were similar to those of the controls. This suggests that in cucumber more of the DNA template is available for transcription. This suggestion was supported by the fact that the incorporation of 14C-adenine into RNA in cucumber roots 10 hr after treatment with dicamba was increased by 50%, whereas in wheat there was no difference. Furthermore, the incorporation of 14C-leucine into protein in cucumber roots 10 hr after treatment with dicamba was inhibited by 70%, indicating that the increased RNA produced was incapable of translating for protein synthesis. It is proposed that selective phytotoxicity of auxin-like herbicides is based on a differential alteration of RNA species and interference with protein synthesis.

Field studies were conducted to document the response of itchgrass [Rottboellia exaltata (L.) L.f. ♯3 ROOEX] in soybean [Glycine max (L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.

Experiments were conducted in laboratory and screenhouse to determine the effects of light, temperature, salt and water stress, seed burial depth, and amount of rice residue on seed germination and seedling emergence of wild bushbean and to evaluate the response of that weed to commonly available POST herbicides in the Philippines. Germination (81 to 85%) was not influenced by light; however, it was higher at 30/20 C (88%) than at 25/15 C (82%) and 35/25 C (80%) day/night temperatures. The sodium chloride and osmotic potential required for 50% inhibition of maximum germination were 149 mM and −0.28 MPa, respectively. Seedling emergence (81%) was similar for seeds placed on the soil surface and for seeds buried up to 4 cm deep. No seedlings emerged from a burial depth of 8 cm. Rice residue applied on the soil surface up to 8 t ha−1 did not affect seedling emergence (72 to 80%) of wild bushbean. The herbicide bentazon provided 100% control of wild bushbean when applied at the three- to five-leaf stages. However, to achieve 100% control by 2,4-D and metsulfuron-methyl + chlorimuron-ethyl, herbicides had to be applied at the three-leaf stage. The information gained from this study can help in developing components of integrated weed management programs for wild bushbean. A deep-tillage operation to bury weed seeds below their maximum depth of emergence and early application of an effective POST herbicide can help in managing this weed in rice fields.

A hand-held hyperspectral radiometer was used to measure differences in reflectance characteristics of 24 Palmer amaranth and 15 pitted morningglory accessions collected from the central and southern United States. A hyperspectral reflectance reading was collected from two mature leaves at 24 and 27 d after emergence (DAE) for each accession. Two analysis techniques, linear discriminant analysis and best spectral-band combination (BSBC) analysis, were performed using various vegetation indices, spectral bands, and individual wavelengths. Differentiation of individual accessions was difficult. Palmer amaranth accession classification accuracies were < 50% using both analysis techniques, except one accession collected in South Carolina (63%), when pooled over data acquisition dates. Pitted morningglory accession classification accuracies were also generally < 50%. Classification accuracies were higher using BSBC analysis at 24 DAE; however, at 27 DAE only one accession resulted in classification accuracy > 30%. These results suggest there are only slight reflectance differences within Palmer amaranth and pitted morningglory accessions. These differences may not be predictable based upon accession origin because of the genetic diversity of Palmer amaranth and pitted morningglory. However, differentiation between Palmer amaranth and pitted morningglory was 100%. Thus, spectral sensors used to differentiate between Palmer amaranth and pitted morningglory do not need to be calibrated for a particular region of the United States, and differentiation between these two species can be made using reflectance characteristics.

Species richness and diversity are important indicators of ecosystem function and may be related to plant community resistance to invasion by nonindigenous species. Our specific objective was to determine the influence of clopyralid plus 2,4-D, glyphosate, and fosamine, at different application rates and timings, on richness and diversity of total species, total native species, and total nonnative species within a Russian knapweed–infested plant community. Twenty-eight treatments (3 herbicides by 3 rates by 3 application timings, and an untreated control) were applied to two sites located along the Missouri River riparian corridor in Montana. Clopyralid plus 2,4-D, glyphosate, and fosamine were applied in June (spring rosette stage of Russian knapweed), July (bud to bloom stage of Russian knapweed), and August (flowering stage of Russian knapweed). Herbicide rates were clopyralid plus 2,4-D at 0.08 (clopyralid) + 0.42 (2,4-D), 0.13 + 0.67, and 0.18 + 0.92 kg ai ha−1; glyphosate at 0.6, 1.2, and 1.8 kg ai ha−1; fosamine at 3.6, 7.2, and 10.8 kg ai ha−1. Density of each species was recorded during June and August of 2001 and 2002. Species richness and Simpson's Reciprocal Index (1/D) were calculated. By August 2002, only the glyphosate treatment (4.6 species m−2) yielded greater total richness over that of the control (3.5 species m−2). At that time, diversity after applying clopyralid plus 2,4-D remained similar to that of the control (1.4), but glyphosate (2.3) and fosamine (2.0) increased total species diversity. Nonnative grasses and forbs accounted for the increases in richness and diversity. Glyphosate may be appropriate for enhancing ecosystem function and possibly niche occupation to preempt reinvasion by Russian knapweed, but restoring native species seems unlikely using any of these herbicides alone.

Onion (Allium cepa L.) and bean (Phaseolus vulgaris L.) seedlings grown in soil treated with DCPA (dimethyl tetrachloroterephthalate) were less susceptible to northern root-knot nematode (Meloidogyne hapla Chitwood) infection than seedlings grown in untreated soil. DCPA treatment of nematode larvae did not alter their pathogenicity. Resistance could be correlated with altered cell structure of the root epidermis, increased root exudate as evidenced by soil adherence, reduced fibrous root development, or both.

Field experiments were conducted in 1992 and 1993 to determine the timing and amount of rainfall required to activate UCC-C4243 applied preemergence. UCC-C4243 at 0, 70, and 140 g ai ha−1 was applied 1, 7, 14, and 21 d before 0.5 or 2 cm of simulated rainfall. Temporary rainshelters protected field plots from natural rainfall during the 21 d dry period. Herbicide activity was determined in the field by seeding lentil, wheat, common lambsquarters, and field pennycress and in the greenhouse by a sugarbeet bioassay of soil samples (0 to 3 cm depth) taken from all plots immediately before irrigation. UCC-C4243 did not injure wheat; however, lentil population was reduced when simulated rainfall occurred within 7 d after application. Lentil injury was greater with higher herbicide rate and higher water level. UCC-C4243 at 70 and 140 g ha−1 reduced populations of both weed species by 75 and 90%, respectively, when either 0.5 or 2 cm simulated rainfall was received within 1 d after herbicide application. Weed control was reduced with a 21 d delay between herbicide application and water activation. The sugarbeet bioassay showed a linear decrease of herbicide activity over time and also with accumulated photosynthetically active radiation. After 17.9 d, herbicide activity on a dry soil surface decreased 50%. Laboratory investigations show that [14C]-UCC-C4243 on glass slides was photodegraded by near ultraviolet light (290 to 400 nm). Volatilization of 14C-labeled herbicide from glass slides was less than 5% after exposure to turbulent air for 48 h.

Assimilate transport in purple nutsedge (Cyperus rotundus L.) was studied using autoradiographic technique. Results show the basic pattern of assimilate distribution was from areas of synthesis to areas of use or accumulation. The initial underground centers of high metabolic activity were replaced as these organs matured, by new centers of actively growing rhizomes, tubers, and roots. The planted tuber did not accumulate assimilates. Treatment of purple nutsedge plants with 2,6-dichlorobenzonitrile (dichlobenil) resulted in accumulation of assimilates in the tubers rather than in young underground tissues. Leaves of treated plants also accumulated labeled assimilate in excess of control plants. Assimilate accumulation in leaves of dichlobenil-treated plants resulted from the destruction of the phloem in the basal portions of the leaf-sheaths. An increase in tuber respiration accompanied an increase in accumulation of assimilates in dichlobenil treated tubers.

A study of the C4 plant itchgrass (Rottboellia exaltata L.f.) grown under 100%, 60%, 25% and 2% sunlight revealed differences in the anatomy and cytology of the foliar mesophyll and vascular bundles associated with shading. In the bundle sheath, shading caused a reduction in thickness of the cell walls, shrinkage of plastids, rearrangement of plastid thylakoids, a reduction in starch deposits and vacuolization of the cytoplasm. In general, plastids and mitochondria retained membrane integrity but underwent stromal deterioration. Shading effects on cytoplasm were similar for mesophyll and bundle sheath cells. Mesophyll chloroplasts lost starch grains and the peripheral reticulum tended to decrease with greater shading. Grana were well developed at all irradiances, although the chloroplasts themselves decreased in size with shading. Movement of mesophyll chloroplasts away from bundle sheath-mesophyll borders was pronounced at 60% sunlight and was progressively greater at the two lower irradiances. These observations suggest that the structural relationships thought to be necessary for the intercellular transfer of C4 acids and the functioning of the C4 photosynthetic pathway were disrupted by shading.