Herbicide-resistant annual bluegrass (Poa annua L.) has become a problem in non-arable land areas. In arable fields, P. annua is frequently of lower priority in weed control program due to the variety of control options available and the relatively modest impact on crop yield compared with other species. In Ireland, postemergence herbicides are not primarily intended for P. annua control, but some herbicides, including the acetolactate synthase (ALS) inhibitor mesosulfuron-methyl + iodosulfuron-methyl, exhibit P. annua activity. In this study, a suspected P. annua population (POAAN-R) that survived mesosulfuron-methyl + iodosulfuron-methyl at 0.75 of the field recommended rate was sampled from a wheat (Triticum aestivum L.) field in County Dublin, Ireland. Single-dose testing confirmed that the suspected POAAN-R had evolved resistance to mesosulfuron-methyl + iodosulfuron-methyl and, additionally, to pyroxsulam (not registered in Ireland for P. annua control), but was sensitive to clethodim, glyphosate, pendimethalin, and flufenacet. Dose–response experiments indicated that POAAN-R was more resistant (GR50 resistance index) to both mesosulfuron-methyl + iodosulfuron-methyl (47.8 times) and pyroxsulam (38.0 times) than sensitive POAAN-S, and this was associated with the mutation at Trp-574 in the ALS protein. Malathion (a cytochrome P450 [P450] inhibitor) pretreatment did not reverse POAAN-R resistance to mesosulfuron-methyl + iodosulfuron-methyl or pyroxsulam at the field rate or above. The natural inherent mutation at Ile-1781 in acetyl-CoA carboxylase protein had no effect on both POAAN-R and POAAN-S sensitivity to clethodim. The glyphosate sensitivity of POAAN-R also corresponded with no known mutation in 5-enolpyruvylshikimate-3-phosphate synthase protein. Based on field histories, poor early-season weed control coupled with intensive use of mesosulfuron-methyl + iodosulfuron-methyl (often at reduced rates) has unintentionally selected for ALS inhibitor–resistant POAAN-R. This is the first report to characterize resistance in P. annua to ALS-inhibiting herbicides mesosulfuron-methyl + iodosulfuron-methyl and pyroxsulam in an arable setting. There is an opportunity to effectively control POAAN-R using herbicides, but this needs a wide-ranging and varied approach, coupled with cultural/nonchemical practices.

Johnsongrass [Sorghum halepense (L.) Pers.] is one of the most noxious weeds distributed around the world. Due to its rapid growth, wide dissemination, seeds that can germinate after years in the soil, and ability to spread via rhizomes, S. halepense is difficult to control. From a perspective of plant pathology, S. halepense is also a potential reservoir of pathogens that can eventually jump to other crops, especially corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench]. As one of the most problematic weeds, S. halepense and its diseases can provide useful information concerning its role in diseases of agronomically important crops. An alternative consideration is that S. halepense may provide a source of genes for resistance to pathogens. While some studies have verified that pathogens isolated from S. halepense actually cause disease on host crops through cross inoculation, similarity of disease symptoms and pathogen morphology have been used for identity of the disease agent in most studies. Availability of DNA sequence information has greatly altered and improved pathogen identification, leading to significant changes in phylogenetic assignments. Reclassification of pathogens, especially fungi, raises new questions concerning the role of S. halepense as a disease reservoir. Our goals in this review are to pinpoint, where possible, diseases for which S. halepense acts as a significant pathogen reservoir and to point out problem areas where further research is needed.

Silvery-Thread Moss (Bryum argenteum Hedw.) is an undesirable invader of golf course putting greens across North America, establishing colonies and proliferating despite practices to suppress it. The goal was to grow genotypes of green (growing in putting greens) and native (growing in habitats outside of putting greens) B. argenteum in a common garden experiment, allowing an experimental test of life-history traits between genotypes from these two habitats. Seventeen collections of green and 17 collections of native B. argenteum were cloned to single genotypes and raised through a minimum of two asexual generations in the lab. A culture of each genotype was initiated using a single detached shoot apex and was allowed to grow for 6 mo under conditions of inorganic nutrients present and absent. Compared with genotypes from native habitats, genotypes of B. argenteum from putting greens exhibited earlier shoot regeneration and shoot induction, faster protonemal extension, longer (higher) shoots, lower production of gemmae and bulbils, and greater aerial rhizoid cover, and showed similar tendencies of chlorophyll fluorescence properties and chlorophyll content. Cultures receiving no inorganic nutrients produced less chlorophyll content, greatly reduced growth, and bleaching of shoots. Mosses from putting greens establish more quickly, grow faster, produce more abundant rhizoids, and yet do not produce as many specialized asexual propagules compared with mosses of the same species from native habitats. The highly managed putting green environment has either selected for a suite of traits that allow the moss to effectively compete with grasses, or genotypic diversity is very high in this species, allowing a set of specialized genotypes to colonize the putting green from native habitats. Successful golf course weeds have been able to adapt to this highly competitive environment by selection acting on traits or genotypes to produce plants more successful in competing with golf course grasses.

Volunteer wheat and downy brome (Bromus tectorum L.) were consistently controlled by aerial applications of granular 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) without supplemental tillage. Injury to winter wheat seeded in the fall 13 and 14 months after application of atrazine has occurred. Plots aerially treated with 2 lb/A atrazine produced yields comparable to the check but plots treated with 4 lb/A atrazine produced no wheat. Use of persistent herbicides for chemical fallow must be restricted until further knowledge is obtained.

Fish used in these tests were the Israeli strain of the common carp, Cyprinus carpio; the Nile tilapia, Tilapia nilotica; the Java tilapia, T. mossambica; and the Congo tilapia, T. melanopleura. Israeli carp and either Nile or Java tilapia in ponds containing only these species virtually eliminated aquatic weeds, but when stocked into established populations of largemouth bass and bluegill results were less encouraging.

Seedling legumes are slow growing plants and poor competitors. During this period of slow growth, weeds have opportunity to outgrow them, and choke out or seriously damage the legume stand. Many of the important weeds are annual broad-leaved plants such as pigweed (Amaranthus retroflexus), lambs-quarters (Chenopodium album), mustards, and certain annual grasses such as the foxtails (Setaria spp.) and crabgrasses (Digitaria spp.). Perennial weeds, when present, are a serious problem, but this study was directed primarily at annuals. Since the advent of the combine, volunteer wheat and oats from shattered grain have also become a serious problem in summer legume seedings after small grain.

Recent reviews [Crafts, Currier, Woodford] dealing with the mode of action of phytotoxic chemicals claim the acute toxicity of petroleum oils to plant tissues is due to the destruction of the plasma membrane of the cell. Although considerable evidence supports such a claim, much of it rests on results from the effect of vapors on greenhouse grown plants rather than on the effect of liquid oils on field grown plants. Of the numerous workers who have noted a selective action of oils on different plant species, most of them determined the selectivity by visual observation of injury. Currier and Peoples, Dallyn, and Van Overbeck and Blondeau linked the selective action by experimentation to a differential effect on a cellular level but only the work of Currier and Peoples included direct determinations of cellular vitality. It seemed desirable, therefore, to obtain further information on the relative susceptibility to petroleum oils of field-grown plants.

Ethyl ester of DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} and butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} applied during the reproductive phase of development at 0.07 and 0.28 kg ai/ha prevented seed formation in downy brome (Bromus tectorum L. # BROTE). Fluazifop prevented seed formation over a wider range of application rates and growth stages than did DPX-Y6202. Seed production was prevented most readily by herbicide applications made early in the reproductive phase. Environmental factors during reproduction affected herbicide performance. Foliar absorption and translocation of 14C-fluazifop into the developing spikelets was greater than that of 14C-DPX-Y6202 in downy brome.

Bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’ and ‘Tifgreen’] were vertically mowed and treated with herbicides alone or in combination at various time intervals during each of 4 yr. All vertically mowed treatments significantly reduced accumulation of thatch, but more than 3 treatments were needed each year for consistently high quality turf. Vertical mowing treatments reduced the accumulation of thatch more than any of the herbicides. Vertical mowing in February prevented a delay in early spring growth of turf. Populations of large crabgrass [Digitaria sanguinalis (L.) Scop.] in the summer and chickweed [Stellaria media (L.) Cyrillo], henbit (Lamium amplexicaule L.), and brome grass (Bromus sp.) in the winter were increased from vertical mowing when herbicides were not applied for control. None of the herbicide treatments injured bermudagrass turf except oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] when applied in the fall.

Reserve polysaccharides were stored at high levels in rhizomes of mugwort (Artemisia vulgaris L.). Polysaccharide level in the rhizome dropped within 24 hr after treatment with 2,3,6-trichlorophenylacetic acid (fenac). Fructosans were hydrolyzed to yield increased levels of simple sugar. Sucrose concentration was slightly lower in treated rhizomes. Glucose was low in untreated rhizomes, and fenac treatment resulted in slight increases in glucose levels. Rhizomes became enlarged, the epidermis was disrupted, and “root primordia” were observed in rows parallel to the main rhizome axis after 1 to 5 days in 10 ppmw of fenac solution. The new primordial growth occurred through activation of the interfascicular cambium.

Absorption, translocation, and metabolism of the methyl ester of 14C-flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] (hereafter referred to as flamprop-methyl) and 14C-barban (4-chloro-2-butynyl-m-chloro carbanilate) in wild oat (Avena fatua L.) were investigated to determine the basis of the synergistic interaction between the two herbicides. The mutual effects of the two herbicides were studied when they were applied together to wild oat at the two- and four-leaf stage. The addition of the commercial formulation of barban, barban formulation additives, technical barban, or the nonionic surfactant polyoxyethylene-6-tridecylether resulted in varying degrees of increase in the absorption of 14C-flamprop-methyl. Translocation of 14C-flamprop-methyl following leaf application in wild oat was mainly acropetal. The addition of commercial barban to 14C-flamprop-methyl did not influence the pattern of 14C translocation. Metabolism of flamprop-methyl by wild oat at either leaf stage was not influenced by barban. Absorption of 14C-barban was increased by the addition of the commercial formulation of flamprop-methyl and by polyoxyethylene-6-tridecylether. The addition of flamprop-methyl did not influence the pattern of translocation and metabolism of 14C-barban in wild oat at either leaf stage. It is concluded that increased absorption of flamprop-methyl and barban by wild oat at the two- and four-leaf stages is the most important factor in the synergistic interaction between these herbicides. Translocation and metabolism of the herbicides do not seem to be important factors in the synergism observed.

Chromatographic procedures were developed for use in the laboratory studies of the breakdown of N-(p-bromophenyl)-N′-methoxy-N-methoxyurea (metobromuron) in soils. Both thin-layer and gas chromatographic procedures were developed to determine the known and/or suspected metabolic products occurring from the microbiological transformations in soil. Extraction of 3 soils, after 5 days of equilibration, yielded all the metabolites. Neither the gas chromatographic or thin-layer procedures were affected by soil extractives.

Field trials were conducted to evaluate the season long population dynamics and location (in leaf or on leaf surface) of an antibiotic resistant strain of the bacterium Pseudomonas syringae pv. tagetis (PST) applied to Canada thistle leaves. An application preceding 2 to 3 d of hot dry weather was compared to an application preceding 2 to 3 d of cool wet weather. Leaf samples were taken weekly to assess the population of PST found inside the leaves and on the leaf surface. While PST populations initially differed, populations were similar for both treatments one week after application. While this suggests that environment did not have a major impact, weather conditions for testing this hypothesis were not ideal. Over the first 35 d of the experiment, little rainfall was observed. PST populations were low and stable. However, rain events over the 40 d that followed resulted in great oscillations in mean PST populations and in some cases significant population increases. During dry periods, internal and total PST populations differed significantly, suggesting the external populations played a major part in population composition. However, the two sampling periods that closely followed three consecutive days of rainfall indicated internal populations were not significantly different from the total, suggesting that internal populations played the primary role in population composition. The results of this research provide evidence that rain events lead to overall PST population increases and to greater proportions of PST inside Canada thistle leaves, suggesting that it is better to apply PST during wet periods than dry.

Dicamba (3,6-dichloro-o-anisic acid) dissipated in 4 weeks and in 9 to 16 weeks when sprayed on grassland soils of Texas at 0.28 kg/ha and 0.56 kg/ha, respectively. At three of four locations ranging from humid to semiarid and from clay to sandy loam and sampled from 9 to 63 weeks after treatment, usually residues were no deeper than 120 cm and never deeper than 150 cm. However, dicamba residues were detected 120 cm deep 53 weeks after application of granules at 1.68 or 2.24 kg/ha to sand of semiarid grassland. Since dicamba sprays are usually applied at 0.56 kg/ha or less for grassland restoration in Texas, it is unlikely that residues of dicamba will persist in soil through the growing season from spring applications.

Greenhouse experiments were conducted to determine the effect of salinity, imazethapyr, and chlorimuron on weed growth. Five species, barnyardgrass, common cocklebur, ivyleaf morningglory, common purslane, and yellow nutsedge, were grown in potting soil and irrigated with nonsaline (EC ∼ 2 dS m−1) or sulfate-dominated saline (EC ∼ 7 dS m−1) nutrient solution. Plants were treated after emergence with imazethapyr (Pursuit formulation) at 70 g ae ha−1 or chlorimuron ethyl (Classic formulation) at 8.8 g ai ha−1. Results indicated that irrigation with saline water had no overall effect on the growth or survival of most tested weed species. Growth of yellow nutsedge (maximum height and stem diameter) was reduced for plants irrigated with saline water. Observed growth and survival trends in saline and nonsaline treatments were consistent with information on the herbicide label. Complete control of common purslane was not achieved by either chlorimuron or imazethapyr. Growth and survival of ivyleaf morningglory and yellow nutsedge were greater when plants were treated with imazethapyr than when treated with chlorimuron, whereas for barnyardgrass, growth and survival were significantly greater when plants were treated with chlorimuron. Both herbicides affected common cocklebur growth and survival in a similar way. For all tested species, most surviving plants were not vigorous and would not be highly competitive with crop plants. The results of these experiments suggest that weed control information mentioned on the labels for these herbicide formulations will not require modification for moderately saline soils.

Field experiments were conducted from 1995 to 1997 to test approaches to managing atrazine-resistant Datura stramonium. Eight weed management programs in a Zea mays and Glycine max rotation were evaluated for their effects on the dynamics of atrazine-resistant and -susceptible D. stramonium populations. Overall D. stramonium density and relative abundance of resistant (R) biotypes were greatly reduced in no-till Secale cereale L. (rye) cover crop management programs without triazine compared to conventional-tillage systems with the application of triazine herbicides. The negative effects of no-till on D. stramonium were greater under a G. max–Z. mays—G. max (SCS) rotation than under a Z. mays–G. max—Z. mays (CSC) rotation. A cropping system involving more G. max phases under no-till reduced both the resistant and susceptible D. stramonium populations. Results from this study support the use of soil management, crop rotation, and negative cross-resistant herbicides to manage atrazine-resistant biotypes.

Weed competition in the commercial production of woody ornamentals results in substantial economic losses annually due to increased labor costs and reductions in plant growth and quality. Container and field experiments were established in 1975 and continued through 1976 to evaluate oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] as a weed control agent and to determine its effect on ornamentals at selected test sites throughout the United States. Test programs were conducted with container and field grown ornamentals at 10 locations during 1975 and subsequently increased to 12 locations in 1976. Rates evaluated included 3.4, 4.5, 5.6 and 11.2 kg/ha. Highly effective control of 17 weeds was obtained for 3-month periods at rates as low as 4.5 kg/ha. Oxadiazon gave commercially acceptable control of common groundsel (Senecio vulgaris L.), a very serious weed problem in containers. Control of common chickweed [Stellaria media (L.) Cyrillo], however, was poor at all rates tested. Ornamental tolerance to oxadiazon was generally excellent. Of the 50 ornamental species evaluated in 1975, only two displayed phytotoxic symptoms; scarlet firethorn (Pyracantha coccinea Roem.) and Chinese privet (Ligustrum sinense Lour.) at 5.6 and 11.2 kg/ha following three successive applications at 3-month intervals. In 1976 trials on 63 species, phytotoxic symptoms could not be reproduced on the above species; chemical intolerance was limited to growth inhibition of aloe yucca (Yucca aloifolia L.) at 5.6 and 11.2 kg/ha.

We studied the early root growth of four Setaria taxa: giant foxtail (Setaria faberi Herrm.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], robust white foxtail (Setaria viridis var. robusta-alba Schreiber), robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber). Growth studies in controlled environments showed significant differences in root elongation among the taxa at three photoperiods. Seminal root lengths after 4 days followed the order presented for selectivity and metabolism of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] (robust white foxtail > giant green foxtail = robust purple foxtail > giant foxtail). Giant foxtail had the greatest root diameter, resulting in the greatest surface area and volume when lengths were equated. The order of seminal root lengths or diameters changed little after 7 days. Robust white foxtail had the most and longest first order lateral roots. Diameter of first order laterals showed giant foxtail > giant green foxtail = robust purple foxtail > robust white foxtail.

The effect of temperature and soil moisture content on the toxicity of soil-applied 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) to sugar beets (Beta vulgaris L. ‘U.S. H-8’) was studied under controlled environmental conditions. High temperatures during or after germination increased the susceptibility of sugar beets to pyrazon while variations in soil moisture content did not have a significant effect. Sugar beet seeds absorbed three times more pyrazon at 35 C than at 18.3 C. During imbibition more than 90% of the pyrazon taken up by sugar beet fruits was concentrated in the pericarps surrounding the seeds. Furthermore, the herbicide which had been accumulated in the pericarp during imbibition did not move into the tissues of the developing seedling during or after germination. Comparative studies showed that there was a lag period in absorption of pyrazon by sugar beet seeds enclosed within their pericarps. This lag period did not occur in sugar beet seeds from which the pericarps had been removed, or in seeds of common lambsquarters (Chenopodium album L.). It is concluded, therefore, that the pericarp contributes to a physical mechanism of selectivity which enables sugar beets to avoid great accumulation of pyrazon when the mechanism of biochemical inactivation of the herbicide is not yet operative.