Effect of intervals between application and tillage on glyphosate control of Cyperus rotundus L.*

Research conducted in El Salvador, Central America, demonstrated that an interval of 3 days between application of glyphosate and tillage was sufficient to cause 90% reduction in purple nutsedge (Cyperus rotundus L.) plants, while delays of 11–23 days generally gave slightly less reduction. à second application to the same plots 35 days following tillage resulted in more than 90% reduction with all intervals. Approximately 3 months after the initial treatment, tuber numbers had been reduced to half the original population. Germination of the remaining tubers was reduced by more than 50%. Glyphosate applied during the dry season caused an average of 79% reduction in plant numbers compared with 88% in the rainy season. However, in the dry season, the remaining plants had no competition from other weeds and after 5 months there was only à 40% reduction in nutsedge population. During the rainy season, 1, 2 and 3 kg/ha were equally effective, but 1 kg/ha was not sufficient in the dry season.     

Effect of glyphosate on the sprouting of Cyperus rotundus L. tubers

Post-emergence applications of glyphosate [N-(phosphonomethyl)glycine] have been shown not to eradicate purple nutsedge (Cyperus rotundus L.) in the field. It was not known if this was due to failure to control emerged plants or if dormant tubers produced new plants after application. Studies with individual plants were conducted in screenhouse facilities to determine the effects of glyphosate rate, time for translocation, area of foliage treated, and shade on the sprouting ability of tubers attached to treated plants. Rates of 1.5–2.0 kg/ha glyphosate inhibited tuber sprouting; 72 h were required for complete translocation at 1.0 kg/ha whereas 36 h were sufficient at 2.0 kg/ha. Treating less than all of the foliage reduced foliar control and increased tuber sprouting. Shading treated plants reduced control of the foliage but did not affect glyphosate translocation to the tubers. These studies showed that glyphosate kills C. rotundus foliage and the tubers attached to treated plants. Therefore, regrowth after glyphosate application under field conditions is due to dormant tubers which sprout after treatment.     

Factors affecting glyphosate activity in Imperata cylindrica (L) Beau, and Cyperus votundus L. I. Effect of soil moisture

Established Greenhouse grown plants of cogongrass Imperata cylindrica (L) Beauv.) and purple nutsedge (Cyperus rotundusL.) were given three different soil moisture regimes; field capacity, moderate stress and extreme stress, followed 6 weeks later by glyphosate [(N-phosphonomeihyl) glydne] applications to the shoots at 0.2,0.4 and 0.8 kg/ha for Imperata and 0.3,0.6 and 1.12 kg/ha for Cyperus. Field capacity watering stimulated most vegetative growth in hoth species. Glyphosate given at field capacity decreased shoot dry weight in both species, and rhizome length, rhizome dry weight and total carbohydrate in Imperata and total number of tuber-bulbs in Cyperus. In contrast. at extreme soil moisture stress, glyphosate showed reduced activity which appeared to be related to the physiological and morphological behaviour of the plants arising from the drought trealment. Application of waier to the roots of the plants grown at soil moisture stress. I week before and I week afler glypbosate spraying, enhanced glyphosate activity, probably because of the recovery of processes disturbed by ibe soil moisture deficit.     

Tuber composition in yellow nutsedge (Cyperus esculentus (L.)) variants

Yellow nutsedge variants from California, Georgia, Illinois, Maryland, Minnesota and Oklahoma were analysed for intraspecific differences in tuber composition. Tuber size varied from 70 to 710 mg. Carbohydrates ranged from 45 to 77% of tuber dry weight. Starch was the most abundant carbohydrate in all the tubers. The saccharides, fructose, glucose, sucrose and melibiose were found at least in trace quantities in all the tubers; only tubers of the Georgia and Maryland variants contained significant quantities of all four saccharides, and the other three variants containted principally sucrose. Triglycerides constituted more than 80% of the lipids in the tubers. The major acid present in all tubers was oleic. Composition du tubercule chez divers biotypes de Cyperus esculentus (L.) Des biotypes de Cyperus provenant de Californie, de Géorgie, de l'Illinois, du Maryland, du Minnesota et de l'Oklahoma ont été analysés en vue de rechercher des différences intraspécifiques dans la composition du tubercule. Le poids du tubercule a varié de 70 à 710 mg. Les hydrates de carbone représentaient de 45 a 77% du poids sec du tubercule. L'amidon a été l'hydrate de carbone le plus abondant dans tous les tubercules. Les saccharides: fructose, glucose, saccharose et mélibiose ont été trouvés au moins à l'état de traces dans tous les tubercules; seuls les tubercules des biotypes de Géorgie et du Maryland contenaient des quantités significatives des quatre saccharides et les trois autres biotypes contenaient principalement du saccharose. Les triglycérides constituaient plus de 80% des lipides des tubercules. Le principal acide gras présent dans tous les tubercules était l'acide oléique. Inhaltsstoffe der Knollen verschiedener Herkünfte von Cyperus esculentus (L.) Herkünfte von Cyperus esculentus aus Kalifornien, Gorgia, Illinois, Maryland und Oklahoma wurden auf Unterschiede in ihrer Knollenzusammensetzung untersucht. Die Knollenge-wichte variierten zwischen 70 und 710 mg. Die Kohlenhydratgehalte schwankten von 45 bis 77% des Knollentrockengewichtes. Stärke war in alien Knollen das häufigste Kohlenhydrat. Die Saccharide Fructose, Glucose, Sucrose und Melibiose waren in alien Knollen zumindest in Spuren festzustellen. Lediglich Knollen aus Gorgia und Maryland enthielten größere Mengen aller 4 Saccharide. DieTestlichen 3 Herkünfte enthielten haupt-sächlich Sucrose. Triglyceride bildeten mehr als 80% der Knol-lenlipide. Die häufigste Fettsäure war Ölsäure.     

Plant growth inhibitors: Patchoulane-type sesquiterpenes from Cyperus rotundus L.

Two sesquiterpene ketones, cyperotundone and α-cyperone, were isolated from dried tubers of purple nutsedge ( Cyperus rotundus L.) as major constituents: ≈0.26% and 0.1% of dried tuber, respectively. These allelochemicals affect plant growth, but we consider that these terpenoids undergo modification when they are released into the rhizosphere from the donor plant. For the structure–activity relationship study, cyperotundone was oxidized with selenium dioxide in acetic acid to 4-patchoulene-2,3-dione and 4-patchoulene-2,3,6-trione. Subsequent hydrogenation of 4-patchoulene-2,3-dione and 4-patchoulene-2,3,6-trione gave hydroxylated derivatives, cyperotundon-2-ol and 3-hydroxy-4-patchoulene-2,6-dione, respectively. 4-Patchoulene-2,3-dione inhibited the hypocotyl growth of lettuce seedlings but promoted radicle elongation at 0.1−2 mg L⁻¹ concentration without chlorosis. Moreover, this radicle elongation recovered with the addition of galactose and was not antagonized by gibberellin A₃. The effect of 4-patchoulene-2,3,6-trione showed a similar chlorosis, caused by 3,6,9-sugetriol triketone, against lettuce seedlings. These ketones did not show the radicle elongation.     

Purple nutsedge tuber sprouting

Purple nutsedge ( Cyperus rotundus L.) tubers remain viable for several years and serve as its principal means of survival. The maintenance of high moisture content is essential to tuber survival. Apical dominance influences bud dormancy within a tuber and in a chain of tubers, and dormancy increases with tuber age. Several growth inhibitors were identified in tubers, but their role in tuber dormancy has not been established. Moisture levels in soil must increase to a critical level before sprouting occurs, but excess soil moisture deters sprouting. Oxygen may be a limiting factor for tuber sprouting in waterlogged soils. Although light is not a requirement for sprouting, it has promoted sprouting. Temperature regulates sprouting; no sprouting occured below 10°C and above 45°C. Optimum sprouting occurred between 25 and 35°C when provided with constant temperatures. However, daily alternating temperatures greatly stimulated sprouting. A daily short duration (0.5 h) of high temperature increased sprouting to nearly 100%, whereas less than 50% sprouting occurred without the daily high temperature pulse. Bud break occurred readily for most tubers at 20°C and in nearly 100% of the tubers with a single 0.5 h exposure to a high temperature (35°C) pulse. However, most buds did not elongate if the tuber remained at 20°C. Bud elongation occurred at higher temperatures, and daily alternating temperatures stimulated shoot elongation up to eightfold greater than at the respective mean constant temperatures. Daily soil temperature fluctuation may be a major signal for purple nutsedge emergence, such as when the plant canopy is removed, or when soils are solarized. Future research is needed to determine tuber sprouting for different ecotypes, and on the role of the rhizome chain. Systems to manipulate sprouting may provide new strategies for purple nutsedge management.     

Effect of soil placement on the activity of herbicides on Cyperus rotundus L. *

The effect of herbicide placemem in the soil on control of Cyperus rotundus L. was studied in the greenhouse with EPTC, alaehlor, norfiurazon, perlluidone, napropamide, trifluralin, and naptalam, EPTC was the mosl active herbicide, increasing the number of sprouts per tuber but inhibitmg bud development at an early stage of growth. The effect was greatest when EPTC was incorporated with the soil around the tubers. The effects of alaehlor were similar, but higher doses were required. Another active herbicide, norfiurazon, was taken up by the roots but its effect was to produce small, chlorotic leaves, Perfluidone was mosl effective when incorporated into the soil around the tubers or when placed in a layer 1 cm above them. Very little effect of napropamide trifluralin and naptalam was observed. In studies of growth and deveiopmenl with different planting depths, C. rotumtus produced basal bulbs, roots and most of its early reproductive parts in a layer of soil 1–3 cm from the surface, irrespective of the depth at which the tubers were planted. Shoots etncrged from 35 im deep but not from 50 cm.     

Effect of anaerobic soil disinfestation amendment type and C:N ratio on Cyperus esculentus tuber sprouting,growth and reproduction

Anaerobic soil disinfestation (ASD) is a cultural technique primarily targeted for control of soilborne plant pathogens, but can also impact weed propagules. A repeated pot study was conducted to evaluate ASD treatment impact on sprouting and growth of introduced Cyperus esculentus (yellow nutsedge) tubers using dry molasses‐based and wheat bran‐based amendment mixtures at four carbon‐to‐nitrogen (C:N) ratios (from 10:1 to 40:1) and compared with a non‐amended control. The mean percentage of sprouted tubers recovered after ASD treatment was lower for wheat bran‐based (42%) than dry molasses‐based (65%) amendments, and tuber production was 1.6‐fold higher in dry molasses‐based than wheat bran‐based treatments. The highest percentage of sprouted tubers (79%) and the highest mean production of large tubers (threefold higher than wheat bran‐based and 1.7‐fold higher than molasses‐based amendments) were observed for the non‐amended control. Tuber sprouting was significantly lower from all ASD treatments (regardless of amendment C:N ratio) compared with the non‐amended control at a 15 cm burial depth. New tuber production was lowest at C:N ratios of 10:1 and 20:1 and more than twofold higher in the non‐amended control. Wheat bran‐based amendments reduced above‐ground C. esculentus biomass compared with the non‐amended control and ASD treatments with molasses‐based amendments, and reduced below‐ground biomass compared with molasses‐based amendments. Above‐ground biomass was highest at amendment C:N ratio of 10:1, and below‐ground biomass was highest at amendment C:N ratio of 40:1 and the non‐amended control. ASD treatment with wheat bran‐based amendments at lower C:N ratios reduced tuber sprouting and reproduction compared with the non‐amended control, but not at rates high enough to use as a primary weed management tactic.     

Control of purple nutsedge (Cyperus rotundus) in cotton with benfuresate

The herbicide benfuresate applied preplanting to cotton (Gossypium hirsutum L.) fields infested with purple nutsedge (Cyperus rotundus L.) inhibited nutsedge growth for several weeks and was found selective for cotton. The best nutsedge control was achieved when the herbicide was mechanically incorporated following a preplant broadcast or band application which was activated by a sprinkler irrigation. The rate of benfuresate needed for effective and selective nutsedge control in cotton ranged from 0.80 to 1.60 kg/ha, the higher rates necessary in soils with higher clay and organic matter contents.     

Studies on the depth distribution and on the germination and growth of Equisetum arvense L (field horsetail) from tubers

Soil core samples taken from a sandy loam soil at Woburn during January 1972, following spring beans during the previous year, indicated that half the rhizome dry weight of Equisetum arvense (L.) occurred in the uppermost 25 cm of soil and 10% between 75 and 100 cm. Tubers occurred relatively more deeply with half the number and three-quarters of the weight deeper than 50 cm. However, after a 2-year fallow 80% of the rhizomes and tubers were in the uppermost 25 cm of soil. In general, the weight of individual tubers increased with increasing depth in the soil. In pots in the glasshouse, tubers that were formed in one season lost weight when new shoots emerged in the following year; those formed during summer germinated readily in warmth indoors when detached in the autumn, but not until June of the following year in the field. Burial of tubers at a range of depths down to 25 cm did not affect the number of shoots emerging but emergence was delayed. Plants made more growth in neutral than in acid or basic soil, more in silty clay loam than in sandy loam and appeared well adapted to growth in soils with little nitrogen. In general, rhizome growth was less affected by variations in pH and nitrogen level than were shoots and tubers. Plants grown from tubers were suppressed greatly by wheat sown densely and given a moderate amount of nitrogen fertilizer but had negligible effect on the wheat. With fewer wheat plants given less nitrogen, the species partitioned more of its assimilate into tubers than when it was grown alone. The significance of tubers in the biology of the species is briefly discussed and areas meriting further study are highlighted.     

Tuber production by purple nutgrass (Cyperus rotundus L.) in darkness

Observations were made on the development of new tubers from sprouts of isolated tubers of Cyperus rotundus grown in the dark. The metabolic events occurred primarily in the sprout itself, though the physiological state of the parent tuber affected the phenomenon. A seasonal variation in the behaviour of the sprouts was observed; maximum tuber formation was found in autumn and winter and minimum in spring and summer. The initiation of new tubers was independent of the sprout length and seemed rather to be dependent on its age. The physiological slate that enabled the sprouts to form tubers alternated with periods in which this condition was lost. Production de tubercules par le cyperus (Cyperus rotundus L.) à l'obscurité Des observations ont été faites sur le développement de nouveaux tubercules à partir de pousses de tubercules isolés de Cyperus rotundus croissant à robscurité. Les transformations métaboliques apparurent dans la pousse elle-même, bien que le phénomène fut affecté par l'état du tubercule parental. Une variation saisonniére fut observée dans le comportement des pousses: la formation maximale des tubercules fut constatée en automne et en hiver, la formation minimale au printemps et en été. L'initiation d e nouveaux tubercules fut indéependante de la longueur de la pousse et sembla plutøt dépendre de son âge. L'état physiologique, qui permet aux pousses de former des tubercules, alterna avec des péeriodes an cours desquelles cette faculté fut perdue. Knollenbildung bei Cyperus rotundus L. in Dunkelheit Es wurde die Entwicklung neuer Knollen aus den Sprossen von isolierten Knollen von Cyperus rotundus beobachtet, die bei Dunkelheit gewachsen waren. Die Stoffwechselprozesse verliefen hauptsächlich im Spross selbst, sie wurden aber vom physiologischen Zustand der Mutterknolle beeinflusst. Das Verhalten der Sprosse war von der Jahreszeit abhängig: die meisten Knollen wurden im Herbst und Winter, die wenigsten im Frühjahr und Sommer gebildet. Die Bildung neuer Knollen war von der Sprosslänge unabhängig und schien eher VOM Alter der Sprosse, abhängig zu sein. Der physiologische Zustand der Sprosse der sie zur Knollenbildung befähigte wechselte mit Perioden ab in denen keine Knollenbildung auftrat.     

Experiments with Cyperus rotundus L. III. Seasonal variations in growth

Nutgrass tubers were planted in pots on thirteen occasions at 4-weekly intervals, and growth and development followed by sampling at 5-day intervals from 10 to 45 days after planting. Growth rates, final shoot numbers, dry weights and rhizome lengths, and new tuber production were highest in plantings made 1 and 29 March and 26 April. Correlation coefficients suggested that mean daylength during growth was a major factor influencing growth and development, but mean temperature appeared to be important in determining new tuber size and the proportion of dry-matter as new tubers. Shoot number appears to be a reliable guide to rhizome and tuber production.     

Metabolic fate of methazole in purple and yellow nutsedge

The mechanisms for the tolerance of purple nutsedge (Cyperus rotundus L.) and susceptibility of yellow nutsedge (Cyperus esculentus L.) to methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] were studied. Both species absorbed and translocated[¹⁴C]methazole and metabolites from nutrient solution; however, greater amounts of ¹⁴C per unit weight were detected in yellow than in purple nutsedge. Although intact plants and excised leaves of both species rapidly metabolized methazole to DCPMU [1-(3,4-dichlorophenyl)-3-methylurea], detoxification of DCPMU to DCPU [1-(3,4-dichlorophenyl) urea] occurred more slowly in yellow than in purple nutsedge. Compared to yellow nutsedge, a greater percentage of the radioactivity in purple nutsedge was recovered as polar products. Polar products were converted to the free forms of the parent herbicide and to phytotoxic DCPMU by proteolytic enzyme digestion. Based on the findings of this study, at least three mechanisms (differential absorption, metabolism, and formation of polar products) account for the differential tolerance of these two species to methazole.     

Unrestricted growth, tuber formation and spread of Cyperus esculentus L. in Zimbabwe

The unrestricted growth and clonal spread from individual tubers of Cyperus esculentus L. were studied in Zimbabwe. Clonal material, collected from the Trelawney area, was grown in a square arrangement in the field with a 5 m spacing between original tubers. Growth was recorded at approximately monthly intervals for 2 years. The natural logarithm of clonal spread (m per month) was positively correlated to temperature and rainfall. Most growth occurred from November to March, a period of optimal moisture and temperature conditions. There was little growth during the remainder of the year. The changes in clonal spread during the year are expressed mathematically and incorporate two parameters of growth; one describes the rate of growth and the other predicts the radius once growth ceases Tuber numbers increased exponentially from December-April, the rate of tuber production being greater in the first than in the second year of growth. Tuber production was greatest during March, April and December, 1980. Dormancy of the tubers decreased during the cooler months from May to August. The value of describing unrestricted clonal growth, and conditions favouring tuber production, are discussed.     

GROWTH,TUBER FORMATION AND SPREAD OF CYPERUS ROTUNDUS L. FROM SINGLE TUBERS*

Summary. Single tubers of Cyperus rotundus L. were planted at intervals over the year. Plant growth was slow and sprouting of tubers was inhibited at temperatures below 20°C, but tubers overwintered at temperatures above freezing point. In the warm season, plant growth and tuber formation rate closely followed air temperature and tubers were forming within 1 month from planting. No inflorescence appeared during the cool season. In autumn-planted C. rotundus grown in containers, the ratio of aerial to subterranean weight decreased from 1·1 in December to 0·2–0·4 in summer. The weight of tubers in mid-summer was about 10 times more than that present in December. Tubers formed at ail times of year and at various locations on plants sprouted readily in laboratory tests (76–100% sprouting). C. rotundus planted in March at wide spacings was grown in field conditions free of other plant competition for 20 months. Within 2 months the plants had spread to 90 cm. At the end of the first and the second summer of growth, the mean area of one plant was 7·6 m² and 56·7 m², respectively, and patches had expanded then by 2·8 m and 5·4 m, respectively, from the initial shoot. After 20 months of growth all tubers were present within the 0–40 cm soil depth, 60–70% of them in the 0–20 cm layer. About 30% of the tubers were within 1 m and 60% within 2 m of the plant centre. Under the patch centre there were about 1000 tubers per m² with 0·3 kg dry weight; in the upper 20 cm more than 3500 tubers weighing 0·9 kg were present per m³ of soil. Croissance, formation de tubercules et propagation de Cyperus rotundus L. issu de tubercules uniques     

Experiments with Cyperus rotundus L.

Tubers of Cyperus rotundus L. were planted in pots, and growth and development followed by washing out every 3 days. New tubers were first recorded 16 days after shoot emergence began, and tuber production proceeded at the rate of one every 4 days. By 51 days a single tuber had produced approximately nine new tubers, nine shoots and nearly 90 cm of rhizome. Treatment with 2,4-D or paraquat at 34 days severely checked shoot growth, but tuber production appeared to he only temporarily checked. Parent tuber dry weight fluctuated between 017 and 0–55 g and the parent tuber appears to act as a source of food in times of stress. Expériences sur le Cyperus rotundus L. I. Croissance et dé-veloppement: effets du 2,4-D et du paraquat Des tuberules de Cyperus rotunds L. ont été plantés dans des pots retires d'où ols lis ont été retirés tous les 3 jours pour en suivre la croissanec et le développement. On a enregistré l'apparition de nouveaux tubercules 16 jours après le début de la levée. La production de tubercules s'est poursuivie á raison d'un tous les 4 jours. Au bout de 51 jours, un tubercule avait produit approximativement 9 nouveaux tubercules, 9 pousses et prés de 90 cm de rhizome. Le traitement avec le 2,4-D et le paraquat au bout de 34 jours a provoqué un freinage important de la croissance de la partie aérienne mais la production des tubercules n'a été ralentie que temporairement. Les poids sees des tubercules initiaux ont varié entre 0.l7 g et 0.55 get ces tubercules paraissent jouer le röle d'une source de maliéres nutritives pendant les périodes difficiles. Versuche mit Cyperus rotundus L. I. Wachstum und Entwick-lung und Wirkung von 2,4-D und Paraquat Knollen von Cyperus rotundus L. wurden in Gefässe gepflanzt und das Wachstum und Entwicklung durch Auswaschen im Abstand von jeweils 3 Tagen verfolgt. Neue Knollen wurden zuerst 16 Tage nach dem Beginn der Sprossbildung beobachtet. Alle 4 Tage wurde eine weitere Knolle gebildet. Nach 51 Tagen hatte eine einzelne Knolle etwa 9 neue Knollen und fast 90 cm Khizom produziert. Eine Behandlung mit 2.4-D Oder Paraquat nach 34 Tagen hemmte das Sprosswachstum stark, aber die Knollenbildung schien nur vorübergehend gehemmt zu sein. Das Trockengewicht der Mutterknollen schwankte zwischen 0,17 und 0,55 g. Die Mutterknolle scheint in Zeiten in denen die Pflanze Belastungen ausgesetzt ist als Nährstoffquelle zu wirken.     

Experiments with Cyperus rotundus L. II. Effects of some herbicides and growth regulators

Soil-incorporated butylate, EPTC and vernolate had only small effects on nutgrass (Cyperus rotundus L.) shoot numbers and the germination of recovered tubers. MSMA, 2,4-D, glyphosate and cyperquat all killed top growth and reduced the germination of recovered tubers in both field and pot trials. Naptalam increased shoot number and tuber production. Foliar sprays of abscisic acid, chlorflurenoi and CCDP (3-carboxy-1-(p-chlorophenyl)-4,6-dimethyl-2-pyridone) had little or no effect. Ethephon slightly increased the number of attached tubers with shoots, but NIA 10637 (.ethyl hydrogen-1-propylphosphonate) had inconsistent efl'ects. MH inhibited tuber bud germination, TIBA increased shoot numbers slightly, and daminozide reduced tuber production and the germination of detached tubers. None of the growth regulators tested appears potentially useful for nutgrass control. Expériences avec le Cyperus rotundus L. II. Action de quelques herbicides et substances de croissance Le butylate, l'EPTC et le vernolate incorporés au sol n'ont eu que peu d'efficacité contre le cyperus (Cyperus rotundus L.) en ce qui concerne le nombre de pousses et la germination des tubercules récoltés. Le MSMA, le 2,4-D, le glyphosate et le cyperquat ont tous détruit la zone terminale de croissance et réduit significativement la germination des tubercules récoltés dans les essais, soit au champ, soit en pots. Le naptalame a augmenté le nombre de pousses et la production de tubercules. Des pulvérisations sur les feuilles d'acide abscissique, de chlorflurénol et de CCDP (3-carbo.xy-1-(p-chlorophényl)-4,6-diméthyl-2-pyridone) n'a eu que peu ou pas d'effets. L'ethéphon a légérement accru le nombre de tubercuies fixés aux racines, mais le NIA 10637 (hydrogéne-1-propylphosphonate d'éthyle) n'a eu que des effets incohérents. L'hydrazide maléique a inhibé la germination du bourgeon du bulbe, le TIBA a accru légérement le nombre de pousses, et le daminozide a réduit la production des tubercules et la germination des tubercules détachés. Aucune des substance de croissance essayées n'apparait potentiellement utilisable pour la lutte contre le cyperus. Versuche mit Cyperus rotundus L. II. Wirkung einiger Herbizide und Wachstumsregulatoren In den Boden eingearbejtetes Butylat, EPTC und Vernolat hatte nur eine geringe Wirkung auf die Anzahl der Sprosse und den Austrieb der Knollen von Cyperus rotundus L. MSMA, 2,4-D, Glyphosate und Cyperquat toteten die oberirdischen Pflanzenteile ab und verringerten den Austrieb der Knollen in Feld- als auch in Gefässversuchen. Naptalam bewirkte eine Zunahme der Sprosszahl und erhöhte die Knollenbildung. Blattspritzungen mit Abscisinsäure, Chlorflurenoi und CCDP (3-Carboxy-1-(p-chlorphenyl)-4,6-di-methyl-2-pyridon) hatten eine geringe oder gar keine Wirkung. Durch Ethephon nahm die Anzahl der Knollen mit Sprossen zu, NIA 10637 (Äthyl hydrogen-1-propylphospho-nat) hingegen zeigte widersprüchliche Wirkungen. MH hemmte den Austrieb der KnoUenknospen, TIBA förderte leicht die Zahl der Sprosse und Daminozid verringerte die Knollenbildung und den Austrieb abgetrennter Knollen. Von den gepruften Wachstumsregulatoren scheint keiner fur die Bekampfung von Cyperus rotundus geeignet zu sein.     

Factors affecting glyphosate activity in Imperata cylindrica (L.) Beauv. and Cyperus rotundus L. II: effect of shade

Imperata cylindrica and Cyperus rotundus were grown under three different light regimes; unshaded, 50% shade, and 75% shade and no shade plus 75% shade before and after spraying, (temporary shade) in a heated greenhouse. Six weeks after the start of the experimenis, glyphosate was applied to the plants at 0·2, 0·4 and 0·8 kg/ha (for Imperata) or 0·3, 0·6 and 1·2 kg/ha (for Cyperus). Glyphosate toxicity was enhanced as shade increased. In Imperata, all shade regimes at all rates of glyphosate eaused greater damage to the plants than the unshaded regime. The reduction in shoot dry weight, rhizome dry weight and total carbohydrate content of Imperate rhizotties at 75% continuous and temporary shaiie conditions, with the lowest rate of glyphosate, was almost twice as much as the reduction in the same features m the unshaded plants caused by the highest rate of glyphosate. In Cyperus. glyphosate at the intermediate and highest rates decreased the shoot dry weight at 75% continuous shade by 79% and 98% respectively. Plants in 50% shade were significantly affected only at the highest rate of glyphosate. Sprouting ability of the tubers al 75% continuous shade was inhibited when the tubers were replanted for recovery. Enhanced toxicity of glyphosate in reduced light intensity was attributed to the morphological changes in the nature of the leaves caused by shade.     

Effects of humidity and moisture stress on glyphosate control of Cyperus rotundus L.*

Glyphosate at 2 kg/ha was more effective in reducing regrowth of purple nutsedge (Cyperus rotundus L.) scapes at 90% than at 50% relative humidity (r.h.), and more effective at ?2 bars than at ?11 bars of plant water potential. Regrowth of treated plants subjected to water potentials of ?1 to ?8 bars was reduced 54–60% while at ?11 bars growth inhibition was only 34%. A time interval of as little as 8 h between application and excision was sufficient to give 47% reduction in regrowth at 90% r.h. None of the treated plants, except those clipped immediately after application, produced new shoots from the basal bulb, while all the untreated control plants produced one or more new shoots. Experiments using ¹⁴C-glyphosate substantiated these results. Three times more ¹⁴C-label was translocated into the underground parts of nutsedge at 90% than at 50% r.h. Twice as much translocated at ?2 bars than at ?11 bars of water potential.     

Chemical control of perennial nutsedge (Cyperus rotundus L.) in tropical upland rice

Five herbicides were tested in the dry and in the wet season for their effectiveness in conlrolling perennial nutsedge (Cyperus rotundus L.) in direct-seeded upland rice in the tropics. K-223 [N-(α,α-dimethylbenzyl)-N'-P-tolyl urea] gave the best results. When broadcast sprayed at 8.0 kg a.i./ha in the dry season and 10 kg a.i./ha in the wet season and immediately mixed into the soit just before drilling, K-223 gave excellent perennial nutsedge control with no visible crop damage and increased the grain yield. Bentazone at 2.0 kg a.i./ha applied 7 days after crop emergence was highly selective and gave fair control of nutsedge without being toxic to the crop. MBR 8251 [1.1,1-trifluoro-4′-(phenylsulfonyl) methane-sulfono-o-toluidide] at 2.0 kg a.i./ha, mecoprop (MCPP) at 1.5 kg a.c./ha and fenoprop (silvex) at 1.0 kg a.e./ha applied 7, 14 and 7 days, respectively after crop emergence provided a fair degree of nutsedge control. Fenoprop and MBR 8251 caused slight and mecoprop moderate initial toxicity, but the injury sustained did not significantly affect crop yield.