Experiments were conducted to determine the influence of water depth, fall flooding, and burial depth on the development of common waterplantain (Alisma triviale Pursh. # ALSPA) in wild rice (Zizania palustris L.). The optimum water depths for common waterplantain from corms were 20 cm when grown outside in submerged pots at St. Paul and 2 and 15 cm when grown in a sloping field at Grand Rapids. Growth of common waterplantain from seeds was maximum at the lowest water depths (2 to 7 cm) at both locations. Wild rice dry weight and seed yield in the same experiments were maximum at the 20- and 30-cm water depths at St. Paul and the 15- and 28-cm depths at Grand Rapids. The increased wild rice seed yield and dry weight at these depths was related to increased tiller production. Wild rice yield was similar at all water depths at Grand Rapids when grown with common waterplantain from corms at a density of 11 plants/m2. Water depths that decreased the effect of common waterplantain interference with wild rice, reduced wild rice yield. Establishment of common waterplantain from corms was maximum at the 5- and 15-cm depths and was severely reduced at the 0- and 30-cm soil depths in soils not flooded in the fall but flooded in the spring. Fall flooding killed all corms regardless of burial depth. Corm mortality under fall-flooded conditions may be due to the effects of ice-encasement.

A technique was developed for evaluating the stability of a herbicide suspended in nitrogen solutions of varying molarity. Dispersion stability is expressed as the difference in specific gravity (D value) between a salt solution + herbicide and the salt solution alone using a Westphal balance. The lower the D value, the less herbicide in suspension. Even very low molar solutions significantly lowered the D value. Further, the lower the percent active ingredient in the herbicide the more effectively the surfactants, and possibly other components of the formulated product, offset the adverse effect of salt on dispersion stability.

The effect of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)], propanil (3′,4′-dichloropropionanilide), and dibromothymoquinone (DBMIB) (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) on proton translocation and photophosphorylation in isolated spinach (Spinacia oleracea L.) chloroplast fragments was investigated. In the absence of added cofactors, O2, or artificial electron acceptors, cyclic electron transport occurred, which was coupled to energy conservation. Under aerobic conditions O2 acted as the terminal acceptor in non-cyclic electron transport. Proton translocation and photophosphorylation in the cyclic process were enhanced by diuron, desmedipham, and propanil, while in the non-cyclic process they were inhibited by all three herbicides. DBMIB inhibited proton translocation and photophosphorylation in both processes. Proton translocation and its enhancement increased with increasing light intensities. The finding that the plastoquinone (PQ) antagonist DBMIB disrupted cyclic as well as noncyclic electron flow, while diuron enhanced the cyclic and inhibited the noncyclic process, indicated that the acceptor site for endogenously-cycling electrons must lie between the active site of diuron inhibition and PQ, The close similarity in the behavior of diuron, desmedipham, and propanil suggests that their site of action is the same.

Plots of western false hellebore (Veratrum californicum Durand), treated in 1968 and 1969 with 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 kg/ha, were reexamined in July 1979 to determine vegetative changes, especially any increases in the production of desirable species and long-term control of western false hellebore. Grass, sedge, and rush production had doubled, and broadleaved plant production, excluding western false hellebore, which was eliminated, decreased on treated plots. Western false hellebore had not reinvaded the treated plots; control remained at 100% for 10 yr. Removal of the western false hellebore on treated plots allowed an increase in grass, sedge, and rush production of 1,500 kg/ha over check plots.

Dicamba (3,6-dichloro-o-anisic acid), 1,1′-dimethyl-4,4′-dipyridinium ion (paraquat), and (2,4,5-trichlorophenoxy)-acetic acid (2,4,5-T) were applied as foliar sprays to 4-year-old sweetgum (Liquidambar styraciflua L.), green ash (Fraxinus pennsylvanica Marsh.), water oak (Quercus nigra L.), and loblolly pine (Pinus taeda L.). For the three hardwood species the amount of herbicide absorbed and translocated, as measured 4 days after application, was correlated closely with tops killed 1 year later. Applications in May were more effective than those made later in the growing season. Loblolly pine was defoliated by all herbicides but recovered the second season after spraying.

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.

Experiments involving the application of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 0.56, 1.12, or 1.68 kg/ha on each of three successive plantings of pickling cucumbers (Cucumis sativus L. ‘Explorer’) were conducted during a 2-yr period. Residues of nitralin in soil increased with rate and number of applications. Nitralin residues accumulated to higher concentrations in a soil with 2.9% organic matter than in a soil with 0.7% organic matter. However, cucumber plants were injured less in the soil with the highest concentrations of herbicide. Oats (Avena sativa L. ‘Carolee’) planted following cucumbers were injured by nitralin residues resulting from the highest application rates. Bioassays and chemical analyses suggested that no appreciable soil residues of nitralin remained during the succeeding year.

Seven cultivars of spring wheat (Triticum aestivum L.) and one hybrid (Triticale hexaploid Lart. ‘Rosner’) were evaluated in seven field experiments and one greenhouse test for tolerance to the postemergence application of the sodium salt of trichloroacetic acid (TCA) for the control of green foxtail (Setaria viridis (L.) Beauv.). The control of green foxtail and broadleaf weeds was also studied. Of the seven cultivars, ‘Pitic 62’ and ‘Stewart’ were most susceptible to injury from TCA. All other cultivars were tolerant to 0.56 kg/ha. ‘Selkirk’ appeared to be most resistant. With ‘Manitou’ 0.56 kg/ha of TCA gave about 50% control of green foxtail. Higher rates permitted increased growth of broadleaf weeds as a result of reduced competition from injured wheat and green foxtail. Control of all weeds was improved by 10 to 30% when TCA was applied with one of the phenoxy herbicides. Satisfactory crop tolerance and good weed control was achieved with 0.56 kg/ha TCA and 0.56 kg/ha of the amine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D).

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.

Western ironweed (Vernonia baldwini Torr.) seedlings emerge from an exalbuminous achene. By 6 days after germination, a cortical collar was discernible between the hypocotyl and root. A pair of lateral buds arose exogenously from the outer two to three layers of this zone through dedifferentiation of cortical parenchyma. Sprouting of lateral buds could be stimulated in a few seedlings by 15 days after germination if they were clipped between the cotyledons and the hypocotyl-root transition zone. One of the seedling buds could be activated by top removal up to 40 days after germination when both could be stimulated to sprout. Ability to form new stems vegetatively was reflected in rate of anatomical maturity of the seedling buds.

Two, 4-dichloro-6-fluorophenyl-p-nitrophenyl ether (CFNP) is similar in herbicidal property and chemical structure to nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether). CFNP inhibits the growth of the hypocotyl and young buds of germinating weeds. Henry Crabgrass (Digitaria adscendens H.B.K. Henr.) was controlled by CFNP at 0.5 kg/ha, however sunflower (Helianthus annuus L.) was tolerant to 16 kg/ha of CFNP. CFNP also effectively controlled largeseed dodder (Cuscuta indecora Choisy) which is a serious problem in sunflower. Although trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) did not control common dodder at 8 kg/ha, CFNP gave control at 0.5 kg/ha.

Glycine max fields with Sesbania exaltata and Senna obtusifolia were selected to evaluate weed effects on insecticide spray droplet deposition within the crop canopy and soybean looper (Pseudoplusia includens) mortality. Weedy and weed-free treatments with and without thiodicarb insecticide application were included. Soybean looper populations in plots with S. exaltata and S. obtusiolia were approximately half those found in weed-free plots. Thiodicarb reduced soybean looper larval survival in the absence of weeds or when weeds were present in three of four experiments. Dye-sensitive cards placed in the top, middle, and bottom thirds of the G. max canopy showed droplet coverage to be highest on cards placed in the top of the canopy. Weeds reduced insecticide coverage in the top of the G. max canopy 26 to 43%. Thiodicarb deposition within the middle and bottom levels of the canopy was not reduced by weeds. Leaflets from the top, middle, and bottom thirds of the crop canopy were collected immediately after insecticide application to bioassay for insecticide deposition. For both years, mortality of soybean looper larvae on leaflets collected from the middle or top of weedy and weed-free G. max treated with thiodicarb was equivalent. Assuming that an economic return can be expected, soybean looper management may not need to be altered when moderate infestations of S. exaltata and S. obtusifolia are present in G. max in late season.

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.

Only 24% of black seed of halogeton (Halogeton glomeratus (M. Bieb.) C. A. Mey.) germinated 2 weeks after collection in October. After 11 weeks of dry storage germination had increased to 60%. During the additional 12 weeks of pregermination treatment, germination did not vary significantly from 60% except for seed stored moist at low temperatures. Ninety to 95% of moist seeds stored at −6 C for 6 weeks or longer germinated within 48 hr; this rate of germination was superior to that of seed collected in December.

Diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl) glycine] applied posttransplant in peppers (Capsicum annuum L.) but preemergence to hairy galinsoga [Galinsoga ciliata (Raf.) Blake # GASCI] controlled the weed at 1.7 to 2.2 kg ai/ha. No serious crop injury or yield reduction was observed when diethatyl was applied to peppers at 9 kg/ha posttransplant or at bloom. Soil ridging, practiced to improve drainage and control the crown rot phase of Phytophthora blight (Phytophthora capsici L.), limited the duration of weed control by disrupting the herbicide-treated surface soil and exposing untreated soil. Diethatyl applied at 2.2 kg/ha posttransplant and again at pepper bloom, after the soil ridges were formed, controlled hairy galinsoga throughout the entire growing and harvest season.

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.

Fosamine [ethyl hydrogen (aminocarbonyl)phosphonate] acted as a chemical inhibitor of shoot growth for periods of up to 3 yr following a single summer application to honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] trees. Anatomical study of field, greenhouse, and seedling mesquite indicated that the inhibition of primary and secondary growth caused by fosamine was due to a general cessation of nuclear activity in apical meristems and in the vascular and cork cambia of this species.