The ability of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] to establish and develop from seed was studied in laboratory and field experiments. Optimum germination temperature was 30 C. Seed incubated at cooler temperatures and then transferred to 30 C germinated equally as well as seed incubated continually at 30 C. Germination was unaffected at moisture stress levels between 0 and −4.6 bars, but was decreased at levels between −4.6 and −12.8 bars. The optimum pH range for germination was between 5 and 7. The greatest emergence of seedlings occurred at a depth of 0.5 cm with no emergence occurring at depths greater than 5 cm. Greater emergence was obtained with a loam than sandy loam at all planting depths except 0.5 cm. Field plots seeded on May 1 gave maximum seed production. Seed production decreased with each 2-week delay in planting. Planting dates of July 10 or later produced no seed. Seed germination was affected little by delayed planting. The following spring, regrowth from plants seeded on June 12 or later was less vigorous than regrowth from plants seeded earlier.

The effects of simulated trampling on shoot morphology and ethylene production of a trampling-tolerant perennial forb asiatic plantain were investigated. Trampling increased the number of leaves or inflorescences per plant, the petiole diameter, and the leaf blade length to width ratio but decreased the leaf blade width to petiole diameter ratio and the inflorescence length. Ramets subjected to trampling produced more ethylene than did nontrampled ramets originating from the same root crown. Moreover, an ethylene releaser ethephon decreased the leaf blade width to petiole diameter ratio and increased the leaf blade length to width ratio, in a manner similar to the changes induced by trampling. These results suggested that trampling-induced ethylene might be closely related to some of the adaptive morphological changes in asiatic plantain in response to trampling.

The absorption and translocation patterns of terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] and propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] were determined in wheat (Triticum vulgare Vill. ‘Kaw’) and sorghum (Sorghum bicolor L. ‘RS 612’). Bioassay studies showed sorghum to be tolerant and wheat susceptible to terbutryn. Absorption and translocation of uniform 14C-labeled terbutryn from 1 to 24 hr after initial treatment showed the roots of sorghum and the foliage of wheat to be the major sites of radioactivity accumulation. Foliage was the major site for propazine accumulation with both plant species. Thin-layer chromatography of extracts from terbutryn-treated plants showed that sorghum contained a higher percentage of metabolic breakdown products in the foliage than did the root systems, and wheat contained a high percentage of intact terbutryn in the foliage and roots. High temperature (32 C) enhanced translocation of terbutryn and propazine in both sorghum and wheat. The susceptibility of wheat and sorghum to terbutryn appears to be correlated with a combination of the factors of accumulation within the foliage of the plant and the ability to degrade the terbutryn molecule.

Field research was conducted in 1999 and 2000 to determine the effect of reduced glyphosate rates on growth and yield of nonglyphosate-resistant cotton. Rates of 9, 18, 35, 70, 140, and 280 g ha−1, representing 0.008, 0.016, 0.031 0.063, 0.125, and 0.25, respectively, of the maximum use rate per application (1,120 g ha−1), were applied to cotton at the two-, five-, or nine-node growth stage. On the basis of visual injury estimates, cotton was more tolerant to glyphosate at the nine-node than at earlier growth stages. Plant dry weight was reduced with 70 g ha−1 of glyphosate or higher, when applied at the two- and five-node growth stages in two of three experiments. Dry weight was not affected by glyphosate at the nine-node stage. Plant height also was unaffected by glyphosate rates below 70 g ha−1, but height reduction was noted for all growth stages by experiment combinations, with the exception of the nine-node application for both experiments in 2000, with herbicide rates of 70 g ha−1 or higher. Cotton maturity delay, as noted by an increase in node above white flower number, was observed only at the highest glyphosate rate applied to two- and five-node cotton in one of three experiments. Percent open boll data analysis indicated a decreased opportunity of observing an open boll with increasing glyphosate rate, and this effect was greater at the five-node compared with the two- and nine-node stages in two of three experiments. Seedcotton yield after all glyphosate applications was equivalent to that for the nontreated control.

A 50-yr study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2- and 15-cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, 19.7, and 24.7 yr later. Viability was determined using germination and tetrazolium tests. By 24.7 yr after burial (YAB), no viable seeds were found for common hempnettle, flixweed, foxtail barley, quackgrass, and wild oat. Bluejoint reedgrass, which had no live seed 19.7 YAB, again had viability (1% at 15 cm) 24.7 YAB. Seeds of 11 other species were still viable: American dragonhead (52%), marsh yellowcress (11 and 3.0% at 2 and 15 cm respectively), common lambsquarters (2.8%), prostrate knotweed (2.8% at 15 cm), shepherd's-purse (2.8%), pineapple-weed (2.6%), rough cinquefoil (2.3%), Pennsylvania smartweed (1.1%), common chickweed (0.4%), wild buckwheat (0.3%), and corn spurry (0.1%). Seed dormancy 24.7 YAB was very low (< 10%) for all species except American dragonhead (99%), shepherd's-purse (40%), marsh yellowcress (23% at 2 cm), Pennsylvania smartweed (18%), and rough cinquefoil (14%). At the beginning of the study, declines in seed longevity were uniform between replicates, but variability between replicates increased over time for all species except American dragonhead, suggesting that some soil microsites are more favorable for seed survival and may be seedbank “safe sites.” Results of this study demonstrate that nonrandom seed mortality contributes to the spatial heterogeneity of seed populations in the soil seedbank.

The sweet potato [Ipomoea batatas (L.) Lam.] cultivars ‘Jewel’, ‘Centennial’, ‘Caromex’, and breeding lines ‘W-70’, ‘W-152’, and ‘Tinian’ (PI 153655) were evaluated for metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as–triazin5(4H)-one] tolerance in greenhouse and field studies. Tinian was the most tolerant line. Its yields were not reduced by 2.2 kg/ha metribuzin in the field. Jewel, Centennial and W-152 were intermediate in response to metribuzin, and W-70 and Caromex were most susceptible. Regression analyses indicated a high correlation between the response of sweet potato cultivars to 0.5 ppm metribuzin incorporated in a potting mix in the greenhouse and their response to 1.1 kg/ha metribuzin applied after transplanting in the field.

Chess, Bromus secalinus L., and downy brome, Bromus tectorum L., are two of the more common and troublesome weedy grasses in the midwest and western states. Downy bromegrass is widely dispersed in Michigan in pastures, meadows, cultivated fields, and roadsides. Chess occurs frequently in grain fields, particularly in the southern part of the state. These two species have been variously described as annual, winter annual, and either annual or winter annual plants.

Transgenic volunteer corn is a competitive weed in soybean that decreases soybean yield at densities as low as 0.5 plants m−2, yet the competitive effects of volunteer corn in corn have yet to be quantified in the peer-reviewed literature. In order to quantify competition between volunteer corn and hybrid corn, seed was harvested from transgenic hybrid corn. The seed was then hand-planted at two locations (Lafayette, IN and Wanatah, IN) into 3 by 9 m plots of hybrid corn at five densities: 0 (control), 0.5, 2, 4, and 8 plants m−2. Volunteer corn competition reduced leaf area and biomass of hybrid corn plants. Hybrid corn grain yield at Lafayette, IN, was reduced by 23 and 22% due to competition with volunteer corn growing in densities of 8 plants m−2 in 2010 and 2011, respectively, but when volunteer corn grain yield was combined with the hybrid corn grain yield, there was no reduction in total grain yield. This study demonstrates that the competitive effects on the grain yield of the hybrid corn will be offset by the grain yield of the volunteer plants. However, because the unpredictable locations and densities of volunteer corn plants present challenges to machine harvesting, future studies should examine what proportion of the volunteer crop is actually harvestable.

Multiple resistance to glyphosate, sethoxydim, and paraquat was previously confirmed in two Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] populations, MR1 and MR2, in northern California. Preliminary greenhouse studies revealed that both populations were also resistant to imazamox and mesosulfuron, both of which are acetolactate synthase (ALS)-inhibiting herbicides. In this study, three subpopulations, MR1-A (from seed of MR1 plants that survived a 16X rate of sethoxydim), MR1-P (from seed of MR1 plants that survived a 2X rate of paraquat), and MR2 (from seed of MR2 plants that survived a 16X rate of sethoxydim), were investigated to determine the resistance level to imazamox and mesosulfuron, evaluate other herbicide options for the control of these multiple resistant L. perenne ssp. multiflorum, and characterize the underlying ALS-inhibitor resistance mechanism(s). Based on LD50 values, the MR1-A, MR1-P, and MR2 subpopulations were 38-, 29-, 8-fold and 36-, 64-, and 3-fold less sensitive to imazamox and mesosulfuron, respectively, relative to the susceptible (Sus) population. Only MR1-P and MR2 plants were cross-resistant to rimsulfuron, whereas both MR1 subpopulations were cross-resistant to imazethapyr. Pinoxaden (ACCase inhibitor [phenylpyrazoline 'DEN']) only controlled MR2 and Sus plants at the labeled field rate. However, all plants were effectively controlled (>99%) with the labeled field rate of glufosinate. Based on I50 values, MR1-A, MR-P, and MR2 plants were 712-, 1,104-, and 3-fold and 10-, 18-, and 5-fold less responsive to mesosulfuron and imazamox, respectively, than the Sus plants. Sequence alignment of the ALS gene of resistant plants revealed a missense single-nucleotide polymorphism resulting in a Trp-574-Leu substitution in MR1-A and MR1-P plants, heterozygous in both, but not in the MR2 plants. An additional homozygous substitution, Asp-376-Glu, was identified in the MR1-A plants. Addition of malathion or piperonyl butoxide did not alter the efficacy of mesosulfuron on MR2 plants. In addition, the presence of 2,4-D had no effect on the response of mesosulfuron on the MR2 and Sus. These results suggest an altered target site is the mechanism of resistance to ALS inhibitors in MR1-A and MR1-P plants, whereas a non–target site based resistance apparatus is present in the MR2 plants.

Legume green manures have been used for millennia as sources of N for succeeding crops, but they are also sources of phytotoxic compounds that may selectively influence the performance of crop and weed species. To determine whether substitution of legume green manure for synthetic N fertilizer could enhance crop yield while suppressing weed growth, we conducted a field experiment in which common bean and wild mustard were sown in monocultures and mixtures. Three soil management treatments were employed: red clover residue, ammonium nitrate fertilizer (84 kg N ha−1), and a control that received neither red clover nor ammonium nitrate. In the absence of wild mustard, bean seed yield was equivalent in the red clover and ammonium nitrate treatments, where yields were 11 to 26% greater, respectively, than in the control. When bean grew in competition with wild mustard, its seed yield was as high (1995 and 1996) or higher (1994) with red clover residue than with ammonium nitrate. Averaged over bean competition treatments, wild mustard biomass production was 37% lower with red clover residue than with ammonium nitrate in 1994, 53% lower in 1995, and equivalent in these two treatments in 1996. Bean seed yield and wild mustard biomass production were strongly correlated with whole-plant N content and more weakly correlated with leaf area duration. Of the variation observed in wild mustard seed production, 89 to 93% was predicted by the variation in wild mustard biomass. The results of this study indicate that substitution of red clover green manure for ammonium nitrate fertilizer can be compatible with bean production goals and can contribute to the management of wild mustard.

The phytotoxicity of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) usually decreased as the stage of growth of five weed species at treatment increased. Giant foxtail (Setaria faberii Herrm.), velvetleaf (Abutilon theophrasti Medic.), and the cotyledonary stage of cocklebur (Xanthium pensylvanicum Wallr.) were most resistant to the herbicide. Ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) and jimsonweed (Datura stramonium L.) were more susceptible to chloroxuron. Soybean (Glycine max (L.) Merr.) seemed less susceptible at the cotyledonary stage than at later stages. Phytotoxicity on both weeds and soybeans was increased by increased temperature and relative humidity following chloroxuron application. The phytotoxicity of chloroxuron also was increased by simulated rainfall in greenhouse studies.

Equimolar concentrations of 4-phenylsulfonyltrifluoromethanesulfono-o-toluidide (hereafter referred to as MBR-8251), S-ethyl dipropylthiocarbamate (EPTC), and 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) were compared using a quartz gravel nutrient culture method for detecting toxicity to yellow nutsedge (Cyperus esculentus L.), okra (Hibiscus esculentus L.), cabbage (Brassica oleracia var. captata L.), cucumber (Cucumis sativus L.), and flax (Linum ustitatissimum L.). MBR-8251 was more active on yellow nutsedge than EPTC or alachlor, and MBR-8251 treated nutlets were controlled for a longer period. In general, crops were more tolerant of MBR-8251. Field studies comparing the effectiveness of MBR-8251 to EPTC, S-propyl dipropylthiocarbamate (vernolate), 2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine (atrazine), 3-isopropyl-2,1,3-benzothiazinone-(4)-2,2-dioxide-6,7,8 (BAS-3510), alachlor, and 2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide (MON-097) indicated that after 10 weeks yellow nutsedge control was excellent with MBR-8251, MON-097, and alachlor.

Old-growth forest in Indiana consists of a few remnant stands in a fragmented agricultural landscape. Old-growth stands can differ substantially from more recently disturbed stands in species composition and may be less susceptible to invasion by exotic plant species. Herbaceous species were sampled in quadrats placed in a repeating pattern along two perpendicular transects in six Old-growth stands in Indiana in spring and summer of 2005. Transects extended from forest edges to the center of each stand. Woody exotic species were sampled in 10-m-wide belts centered on each transect during the summer sampling run. Herbaceous exotic species were a minor component of the understory community in all stands and accounted for less than 1% of total herbaceous cover in all six stands. Exotic woody species generally followed a similar pattern. Four sites contained no more than two woody exotic species, and these were encountered at relatively low frequencies and densities. However, European privet and multiflora rose were present in 27 and 48% of quadrats in one stand, respectively. Thus, although both herbaceous and woody exotic species were relatively rare, heavy infestations of woody exotic species are possible. This suggests that, for some Old-growth sites, exotic species can overcome both local and landscape factors that limit their abundance.

Sicklepod is a competitive and prolific weed that emerges throughout the crop season. Glyphosate applications to flowering sicklepod greatly reduce seed production, but there is limited information on glyphosate translocation in flowering weeds. Therefore, a laboratory study was conducted to document the absorption and translocation of 14C-glyhosate in flowering sicklepod. Flowering sicklepod plants were treated with a 14C-glyphosate solution, and 14C-glyphosate absorption and translocation was quantified by scintillation spectrometry. Absorption and translocation of 14C-glyphosate in flowering sicklepod were similar for both 0.21 and 0.42 kg ae ha−1 glyphosate. Although the treated leaflets retained approximately 50% of the recovered 14C-glyphosate, movement of the herbicide was both acropetal and basipetal, with the highest 14C-glyphosate concentrations in the shoot below the treated leaf and the roots. By 96 h after treatment, sicklepod buds and flowers had abscised, but analysis of the structures revealed accumulation of 2% of the recovered 14C-glyphosate. Based on results of the study, effects of glyphosate accumulation in buds and flowers combined with plant stress associated with the primary and secondary effects of glyphosate result in bud and flower abscission, drastically reducing sicklepod seed production.

Two overhead applications of monosodium methanearsonate (MSMA) at either 4 + 4 or 4 + 2.5 lb/A were required for effective postemergence control of rhizome johnsongrass (Sorghum halepense (L.) Pers.) in ratoon sugarcane (hybrids of the genus Saccharum). Two applications of MSMA in the spring controlled 95% of the johnsongrass, whereas two applications of 2,2-dichloropropionic acid (dalapon) at 4.5 lb/A, the standard treatment, controlled only 70%. In heavily infested fields, sugarcane treated with MSMA also outyielded sugarcane treated with dalapon. Sugarcane tolerated MSMA applied before June; the yield of weed-free sugarcane treated with MSMA was not significantly less than that of the untreated control. However, most MSMA treatments, particularly those applied in late spring, caused temporary leaf chlorosis and stunting. Sugarcane sprayed with MSMA before June generally contained no more arsenic in the juice and bagasse at harvest than untreated sugarcane. Application of MSMA in June or August increased the arsenic content, and resulted in concentrations up to 0.45 ppm in juice, and up to 1.68 ppm in bagasse.

Injury to navy bean (Phaseolus vulgaris L.) from EPTC (S-ethyl dipropylthiocarbamate) was investigated as a function of soil moisture, planting depth, soil compaction, temperature, available nitrogen, and seed quality. Experiments in the greenhouse and growth chamber showed that both high and low moisture stress increased injury. Deep planting increased the injury from high rates of EPTC. Soil compaction alone reduced plant growth. In combination with EPTC at 4.5 kg/ha, further growth reduction was observed. Ambient temperature did not alter susceptibility to EPTC. Stimulation of growth by nitrogen as measured by increased fresh weight was inhibited by EPTC. Field and greenhouse studies showed that EPTC injury was greater to mechanically damaged seed than non-damaged seed.

The possibility of using the fungus Bipolaris sacchari as a bioherbicide to suppress cogongrass and to allow the establishment of bahiagrass in cogongrass–bahiagrass mixed plantings was investigated under greenhouse conditions. The bioherbicide was prepared by mixing B. sacchari spore suspension containing 105 spores ml−1 with an oil emulsion composed of 16% horticultural oil plus 10% light mineral oil and 74% sterile water. The bioherbicide caused severe foliar blight in cogongrass and slight phytotoxic damage on bahiagrass. In the first experiment, the bioherbicide reduced cogongrass biomass without affecting bahiagrass biomass. In the second experiment, the bioherbicide caused a 64% reduction in fresh weight, a 74% reduction in the number of rhizomes, and a 47% reduction in the height of cogongrass. The latter experiment also showed an increase in bahiagrass fresh weight in the presence of cogongrass when the bioherbicide was applied. This study indicates the potential of combining bioherbicide application with competition from a desirable grass species as a strategy for the integrated management of cogongrass.

Potassium azide (KN3) was shown to have potential use as a soil fumigant based on the evidence that azide killed dormant seeds in laboratory and field experiments. Volatility was an important factor in the dissipation of KN3; an acid environment greatly increased volatility probably due to rapid conversion to HN3, whereas soil type exerted little influence on vapor loss. Increasing the soil moisture decreased volatility due to water solubility of NH3. KN3 was leachable and weakly adsorbed in various soil types and at different pH levels. From experiments using stoppered flasks to exclude volatility, it was concluded that the dissipation of KN3 was a chemical phenomenon accelerated by elevated temperatures. KN3 dissipated rapidly from an acid soil whether autoclaved or non-autoclaved; however, alkaline soils prevented dissipation of KN3. Apparently, KN3 is converted to HN3 before it is decomposed. Diffusion within the soil was restricted and occurred only in an acid soil. Covering the soil with plastic immediately after application reduced volatility and increased the biological activity of KN3.

Lateral roots of a clone of field bindweed (Convolvulus arvensis L.) were dug each month for 12 months, cut into 6-cm long sections and grown in the dark on moist paper at 23 C to determine if regeneration varies seasonally. New shoots and roots were measured after 8, 11, and 14 days. After 14 days, 69% to 98% of the sections had produced shoots. The mean number of shoots per section was greatest in April (6.4) and least in November (2.0). The monthly mean shoot length ranged from 24 to 43 mm. Although most sections produced shoots, very few produced roots. In May, 31% of the sections grew roots, but only 2% to 16% had new root growth in the other months. For the test period, 83% of the sections produced shoots and only 10% produced roots.

Pesticide retention by eight inorganic soil amendments, the majority of which are used in turf, was evaluated using a laboratory-based technique with radiolabeled pesticides. Amendments evaluated were derived from various naturally-occurring deposits of zeolites, diatomaceous earths, and fired clays and are intended to provide long-lived, stable, and uniformly sized particles that can contribute favorable water- and nutrient-retention properties to the root zone. Sand, sedge peat, and a Marvyn loamy sand soil (Ap horizon) were included for comparative purposes. Pesticides evaluated included the herbicides imazaquin and oxadiazon and the fungicide/herbicide fenarimol. Pesticide retention was evaluated with a soil solution technique. Amendments evaluated had considerable variation in cation exchange capacity (CEC), effective CEC (ECEC), surface area (SA), and field capacity with lesser variation in particle size distribution and particle density. Scanning electron microscopy revealed that surface texture was variable but frequently rough and porous. Pesticide retention was also variable but generally more than that of sand and frequently equivalent to sedge peat. Only with fenarimol and amendments that had been Ca+2-saturated could retention be correlated with any of the individual physical or chemical parameters that are generally assumed to govern pesticide adsorption, which in this case were CEC and SA. Imazaquin retention by unaltered amendments was correlated only with the products of SA and CEC, and SA and ECEC. Retention of both oxadiazon and fenarimol by unaltered amendments could not be correlated with any individual physical and chemical parameters or products thereof. Pesticide retention by these amendments is probably the cumulative sum of both true adsorption and physical entrapment.