Control of Elymus repens by rhizome fragmentation and repeated mowing in a newly established white clover sward

Control of perennial weeds, such as Elymus repens, generally requires herbicides or intensive tillage. Alternative methods, such as mowing and competition from subsidiary crops, provide less efficient control. Fragmenting the rhizomes, with minimal soil disturbance and damage to the main crop, could potentially increase the efficacy and consistency of such control methods. This study's aim was to investigate whether fragmenting the rhizomes and mowing enhance the control of E. repens in a white clover sward. Six field experiments were conducted in 2012 and 2013 in Uppsala, Sweden, and Ås, Norway. The effect of cutting slits in the soil using a flat spade in a 10 × 10 cm or 20 × 20 cm grid and the effect of repeated mowing were investigated. Treatments were performed either during summer in a spring‐sown white clover sward (three experiments) or during autumn, post‐cereal harvest, in an under‐sown white clover sward (three experiments). When performed in autumn, rhizome fragmentation and mowing reduced E. repens shoot biomass, but not rhizome biomass or shoot number. In contrast, when performed in early summer, rhizome fragmentation also reduced the E. repens rhizome biomass by up to 60%, and repeated mowing reduced it by up to 95%. The combination of the two factors appeared to be additive. Seasonal differences in treatment effects may be due to rhizomes having fewer stored resources in spring than in early autumn. We conclude that rhizome fragmentation in a growing white clover sward could reduce the amount of E. repens rhizomes and that repeated mowing is an effective control method, but that great seasonal variation exists.     

Response to flooding intensity in Elytrigia repens, E. intermedia (Poaceae: Triticeae) and their hybrid

Response to flooding intensity in three closely related taxa, Elytrigia repens, E. intermedia and their hybrid was studied. Plants were exposed to three intensities of flooding for a 30‐day period. Response to flooding intensity was estimated by measuring dry mass of the following: total biomass, above‐ground living biomass, above‐ground dead biomass, below‐ground biomass, rhizome and root mass and by the allocation of dry mass into rhizomes and root:shoot ratio. Reduction of nearly all the biomass compartments with increasing flooding intensity was observed in the three taxa. All three taxa can thus be regarded as flood‐intolerant. Based on the parameters measured, E. repens is regarded as the relatively most flooding‐tolerant, E. intermedia as the least tolerant, while the hybrid displayed intermediate flooding tolerance. The higher flooding tolerance in E. repens was likely related to its ability to accumulate a sufficient mass of rhizomes before flooding, due to higher regeneration ability. E. repens also displayed the highest phenotypic plasticity, as deduced from the reaction norms constructed for total biomass and rhizome mass of particular clones of the three taxa studied. This indicates that, on the species level, E. repens is better adapted to changing environmental conditions and it can be expected to colonize flooded soils. Both Elytrigia species also occur as weeds: E. intermedia grows in agricultural environments in warm regions, while E. repens infests many different types of habitats. Where they co‐occur, hybridization between them may lead to the enrichment of their gene pools with genes responsible for survival of the parental species under extreme conditions; their weedy potential may thus be enhanced.     

Seasonal variation in sprouting capacity from intact rhizome systems of three perennial weeds

The three rhizomatous perennials Elytrigia repens, Equisetum arvense and Tussilago farfara are all problematic in Scandinavian agriculture, due to their low susceptibility to soil cultivation. While repeated soil tillage is a fundamental part of the integrated control of these species, it is highly energy consuming and inefficient during periods when little sprout regrowth occurs. Substituting cultivation with mowing will reduce the environmental impact and labour costs, but its efficiency will still depend on the capacity of plants to sprout. Therefore, we studied the seasonal pattern in emergence and rhizome biomass allocation from July to April in six populations for each of the species. Plants were grown outdoors in pots buried in soil and exhumed at regular intervals in a two‐year experiment. In all three species, biomass allocation to rhizomes continued until late in the autumn. Emergence was severely impaired in E. arvense and T. farfara in September–October, while in E. repens, there was no such reduction in the number of emerged shoots. However, in the latter species, the shoot/rhizome ratio decreased and remained low until the plants had been exposed to a period of low temperatures. The increase in shoot/rhizome ratio for E. repens coincided with the resumed capacity to emerge for E. arvense and T. farfara. These results imply that there is no need to repeat a defoliation of E. arvense and T. farfara, if carried out in September–October. However, removal of the aerial plant parts early in the autumn is important to interrupt the upload of storage compounds to the rhizome systems of all species.     

Effects of repeated applications of fluazifop-butyl, haloxyfop and sethoxydim on Elymus repens in strawberries

Fluazifop-butyl, haloxyfop and sethoxydim with adjuvant oil were applied for three successive growing seasons to established strawberries infested with Elymus repens. The weed was virtually eradicated by three applications of haloxyfop (0.8 kg a.e. ha^?1) in successive years. A similar effect was given by five applications of haloxyfop (0.4 kg a.e. ha^?1) and fluazifop-butyl (1.6 kg AI ha^?1) in three growing seasons. Lower rates of haloxyfop and fluazifop-butyl, and a high rate of sethoxydim (1.6 kg AI ha^?1) applied five times were less effective, the ground cover of E. repens shoots not being reduced by the end of the experiment although weight of living rhizome was only 10-30% of that on untreated plots. Fruit yields on treated plots generally reflected the level of E. repens control, but there was some evidence of crop phytotoxicity from herbicide treatments. During the experiment E. repens untreated plots increased from about 30-100% ground cover and reduced yield 13, 28 and 68% in successive years compared with weed-free plots.     

Fate of glyphosate in Agropyron repens (L.) Beauv. growing under low temperature conditions

Absorption, translocation and distribution of ¹⁴C-glyphosate were examined in Agropyron repens (L.) Beauv. plants growing under field conditions in the autumn. Glyphosate absorption did not increase beyond 3 days after application, whereas translocation to the rhizomes continued up to 7 days after application. The translocated glyphosate accumulated more in new rhizomes than in older parts of the rhizomes. Ten per cent of the glyphosate translocated out of the treated shoot was recovered in younger shoots 7 days after application. Plants harvested the following spring contained less than 20% of the glyphosate originally applied. Although a growth cabinet experiment indicated that 34% of the glyphosate in the rhizomes of treated plants could be remobi-lized into new aerial shoots, considerably less was recovered in new, aerial shoots in the spring in the field-grown plants. Freezing experiments showed that glyphosate translocation to the rhizomes was only prevented when cold treatment caused visible damage to A. repens foliage.     

Growth of seedlings of Agropyron repens (L.) Beauv. and Agrostis gigantea Roth in cereal crops

Experiments were undertaken to define the conditions under which seeds and seedlings of Agropyron repens and Agrostis gigantea may start infestations in cereal crops. When seedlings were planted early or late in spring wheat and spring barley, most growth of shoots and rhizomes was produced by Agropyron planted early in wheat. Late planting halved the amount of shoot growth and severely inhibited rhizome formation. In winter wheat given a moderate or zero amount of nitrogen fertilizer in spring, growth of the weed seedlings was slow. Rhizomes were not produced during the time the crop was growing but only after harvest. Agrostis made more growth than Agropyron in most treatments throughout most of the experiment. Late planting decreased growth more than in the spring cereals. Nitrogen fertilizer, although it had little effect on the amount of growth made by winter wheat, increased the growth of the early-planted seedlings but decreased that of the late-planted ones of both weed species. When planted into plots given nitrogen, more seedlings of both species died after late than after early planting. Clearly, the amount of growth and rhizome produced by seedlings of these two species will depend on the type of cereal, the time of emergence of the seedlings in relation to the cereal, and on other factors affecting the relative vigour of cereal and weed. Evidently, where the weed seedlings emerge early in weakly or moderately competitive cereal crops or when growth is unchecked in the cereal stubble, seedlings could give rise to infestations.     

Combining mechanical rhizome removal and cover crops for Elytrigia repens control in organic barley systems

Mechanical weed control of perennial weeds in organic crop production over long post‐harvest periods is incompatible with the establishment of cover crops for improving soil quality and preventing nutrient leaching. We suggest a new concept that comprises uprooting and immediate removal of vegetative propagules located within the plough layer to allow for quick re‐establishment of a plant cover. A field experiment comparing the effects of conventional practices (stubble cultivation) with different combinations of rotary cultivation (One, Two or four passes) and cover crops (none vs. rye‐vetch‐mustard mixture) on Elytrigia repens rhizome removal, shoot growth and suppression of a subsequent barley crop was examined in two growing seasons. Four passes with a modified rotary cultivator, where each pass was followed by rhizome removal, reduced E. repens shoot growth in barley by 84% and 97%. In general, the cover crop developed poorly and did not affect barley or E. repens. Barley yield was only affected by treatments in the first season, where yield was negatively correlated with E. repens shoot biomass. The concept has potential for the control of severe E. repens infestations, but future research aimed at identifying more effective smother crops and less intensive methods of rhizome removal is needed.     

Under‐sown cover crops and post‐harvest mowing as measures to control Elymus repens

Two potential control methods for Elymus repens, which do not disturb the soil, are post‐harvest mowing and competition from under‐sown cover crops. Our aim was to quantify the effect of cover crop competition and mowing on E. repens and to evaluate the potential for combining the two methods. We present a two‐factorial split‐plot experiment conducted at three locations in Sweden, in two experimental rounds conducted in 2011–2012 and 2012–2013. A spring cereal crop was under‐sown with perennial ryegrass, red clover or a mixture of the two (subplots). Under‐sown crops were either not mowed, or mowed once or twice post‐harvest (main plots). This was followed by ploughing and a new spring cereal crop the next year. Mowing twice reduced autumn shoot biomass by up to 66% for E. repens and 50% for cover crops compared with the control, twice as much as mowing once. Pure ryegrass and mixture treatments reduced E. repens shoot biomass by up to 40% compared with the control. Mowing twice reduced rhizome biomass in the subsequent year by 35% compared with the control, while the pure red clover treatment increased it by 20–30%. Mowing twice and treatments including red clover resulted in higher subsequent grain yields. We concluded that repeated mowing has the potential to control E. repens, but a low‐yielding cover crop has insufficient effect on rhizome biomass. Clover–grass mixtures are of interest as cover crops, because they have the potential to increase subsequent crop yield and even at low levels they reduce E. repens above‐ground autumn growth.     

SPATIAL GROWTH OF SORGHUM HALEPENSE (L.) PERS.*

Summary. Small plants of Sorghum halepense (L.) Pers. were planted in the field and grown without competition from weeds and crops for 2½ years. The plant spread by means of subterranean rhizomes from which aerial shoots developed at increasing distances from the plant centre, and by tillering around these aerial shoots to form clumps. No preferential direction of expansion was detected and established patches developed an approximately circular shape. Aerial growth stopped completely in the cold season. During the warm season the mean area increment amounted to 1·3 m²/month and was similar in both years of observations. After 2½ years of growth, patches had extended up to 3·4 m from the initial sprig and had a mean area of 17 m². In the second summer of growth, shoot density reached 190/m² and mean seed production was 84 g, or 28 000 seeds per plant. About 80% of rhizome dry weight was present in the upper 20 cm of soil and rhizomes did not penetrate deeper than 40 cm. About 80% of rhizome dry weight was present within 1 m radius from the plant centre. Croissance dans l'espace de Sorghum halepense (L.) Pers.     

Johnsongrass (Sorghum halepense) growth characteristics as related to rhizome length

Growth characteristics of johnsongrass [Sorghum halepence(L) Pers] grown in the field from rhizomes 2.5, 5, 10, 15, 20, or 25 cm long were studied in a sandy loam soil for 2 years. Plant height, number of leaves per plant, number of tillers per plant, and fresh weight of new rhizomes and shoots were significantly dependent on the length of the planted rhizome 20, 40, 60, or 80 days after planting. All growth characteristics increased significantly as the length of planted rhizome increased from 2.5 cm to 10 cm to 25 cm Growth characteristics of Johnsongrass plants grown on rhizomes of adjacent lengths (differing by 5 cm) generally were not significantly different. Longer rhizomes (15, 20, or 25 cm) initiated new rhizome growth much earlier (about 20–30 days) than shorter rhizomes (2.5, 5, or 10 cm) Although all rhizome lengths showed a parallel growth potential, the lunger rhizomes were capable of more and faster growth, especially early after planting. It is suggested that Johnsongrass plants associated with longer rhizomes in the field as a result of limited tillage, coupled with their faster growth rate, are expected to interfere with crop production earlier than plants on shorter rhizomes unless controlled.     

Pre-treatment environmental effects on the uptake, translocation, metabolism and performance of fluazifop-butyl in Elymus repens

The performance of fluazifop-butyl against Elymus repens (L.) Gould was significantly influenced by the environmental conditions in which the plants had grown prior to treatment as follows: soil moisture deficit (greatest reduction of herbicide performance) > cool temperatures > low light intensity. The level of control under conditions in which none of these factors was reduced (so-called ‘standard’ conditions) was similar to that observed for‘low light’regime plants. Significant effects of environment on spray retention, foliar uptake and amounts of herbicide translocated to the roots and rhizomes were observed. The lowest rates of herbicide uptake were found with plants grown under cool conditions, the greatest amount of basipetal herbicide translocation being associated with low light intensities. Rates of herbicide de-esterification were much lower in plants grown under low light intensities, cool temperatures, or soil moisture deficits than in those plants grown under the ‘standard’ conditions. This result was confirmed by studies of herbicide deesterification using cell-free leaf homogenates.     

Effects of ethephon pre-treatment on the response of Elymus repens to fluazifop-butyl

Growth inhibition of pot-grown Elymus repens (L.) Gould by fluazifop-butyl was occasionally enhanced by pre-treatment with ethephon. Studies with ¹⁴C-labelled fluazifop-butyl showed that ethephon increased the accumulation of ¹⁴C in basal buds and proximal parts of the rhizome system. This potential modification in the distribution of fluazifop-butyl within E. repens rhizomes may have reduced regeneration and recovery of the E. repens, particularly from the basal buds, although there was no increase in the proportion of ¹⁴C translocated into the rhizome. Also, ethephon not only activated the sinks in the rhizome but in the foliage of E. repens as well, and could initiate buds without sinks. The effects of ethephon on fluazifop-butyl phototoxicity were irregular in their occurrence and degree, and possible reasons for this are discussed. Effets depré-traitements à I'étéphon sur la réponse de Elymus repens au fluazifop-butyl Lors d'expériences en pots, des pré-traitements & 1'étéphon augmentaient occasionnellement 1'inhibition de croissance d'Elymus repens (L.) Gould traité au fluazifop-butyl. Des etudes avec du fluazifop-butyl marqué au ¹⁴C ont montré que l'éléphon augmentait l'accumulation de ¹⁴Cdans les bourgeons de la base et dans les parties proximales des rhizomes. Bien que la proportion de ¹⁴C transportée dans le rhizome ne soit pas accrue, cette modification de la distribution du fluazifop-butyl à l'intérieur des rhizomes d'E. repens pourrait limiter la régénération et la reprise de croissance, en particulier à partir des bourgeons de la base. En outre, l'étéphon activait des puits métaboliques non seulement dans le rhizome mais aussi dans le feuillage d'E. repens et pouvait initier des bourgeons qui ne se comportaient pas comme des puits métaboliques. Tant 1'existence que 1'intensité des effets de 1'étéphon sur la phytotoxicité du fluazifop-butyl étaient irréguliers et les raisons possibles en sont discutées. Wirkung einer Vorbehandlung mit Ethephon auf die Reaktion von Elymus repens (L.) Gould auf Fluazifop-butyl In Gewächshausversuchen war die Wuchshem-mung von Elymus repens durch Fluazifop-butyl gelegentlich durch eine Vorbehandlung mil Ethephon verstärkt. Untersuchungen mil ¹⁴C-Fluazifop-butyl ergaben, daß Ethephon die Ak-kumulation von ¹⁴C in basalen Knospen und proximalen Teilen des Rhizoms förderte. Die so mögliche Veränderung der Verteilung von Fluazifop-butyl in den Quecke-Rhizomen kann zu der reduzierten Regeneration der Pflanzen geführt haben, vor allem aus den basalen Knospen, obwohl insgesamt keine groBere ¹⁴C-Menge im Rhizom gefunden wurde. Ethephon aktivierte nicht nur die Sinks im Rhizom, son-dern auch in den oberirdischen Teilen und kon-nte zur Ausbildung von Knospen ohne Sinks führen. Die Wirkungen des Ethephons auf die herbizide Wirkung des Fluazifop-butyls war unregelmaßig, und die moglichen Grunde dafiir werden diskutiert.     

Regeneration of yarrow (Achillea millefolium L.) rhizome fragments of different length from various depths in the soil

The regenerative response of the rhizomes of Achillea millefolium L. to fragmentation and burial was studied in field experiments on three different soils. The percentage of buds producing shoots (estimated from surviving rhizome fragments) from 4 cm (1·6 nodes), 8 cm (3·8 nodes) and 16 cm (6·7 nodes) rhizome fragments was 63, 44 and 32 respectively averaged over all soils and depths of 5, 10 and 15 cm. The depth at which 50% of the fragments failed to produce an emerged shoot (LD₅₀ depth) was 9·3, 12·4 and 17·9 cm for 4-, 8- and 16-cm fragments respectively averaged over all soils. No fragments survived on the soil surface. The time of emergence of the first shoots was delayed and the rate of emergence and ultimate shoot population reduced with increasing depth of burial. Dry-matter production by aerial shoots and new rhizomes decreased linearly with depth of burial of the rhizome fragments. Soil type had no effect on the regeneration of the fragments. The significance of the results for the control of A. millefolium is discussed.     

Spray Application in Plantation Crops

Abstract

The effects of intraspecific competition on the growth, development and resource‐allocation of Panicum repens was studied under greenhouse conditions. Evidence of severe intraspecific competition and adjustments to plant growth as a response to stress caused by competition, was seen from fairly early stages. An eight‐fold difference in initial plant density per pot, did not produce a significant difference in the dry weight accumulation between densities by 16‐weeks. Increase in plant density resulted in a very significant decrease in dry weight accumulation on a per plant basis, as expected. In general, dry weight partitioning into rhizomes and inflorescences increased with time at all densities, with a concomitant decrease in the percent dry weight partitioned into roots and shoots. Under low density conditions more dry weight was partitioned into inflorescences than at higher densities, indicating a shift in resource‐allocation with changing density. However, the expected shift of dry weight partitioning towards rhizome production at the highest densities was not evident. Allocation of resources to rhizomes did not vary with density. Even the lowest density plants which were not subjected to competitive stress, and the plants at the highest density, all allocated about one fifth of their dry weights to rhizomes. Plants under the highest density stress showed a very significant reduction in the number of tillers they produced and tiller dry weights, on both per pot and per plant basis. The study provides several insights into the highly adaptive and competitive nature of the grass weed, which contribute greatly to its success as a species.     

Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens

Brandsæter LO, Fogelfors H, Fykse H, Graglia E, Jensen RK, Melander B, Salonen J & Vanhala P (2010). Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens. Weed Research 50 , 102–109.

Summary

The success of weed management aimed at depleting the regenerative structures of perennial weeds depends largely on the sprouting activity of rhizome and root buds. Seasonal variation in sprouting of these buds on Cirsium arvense, Sonchus arvensis and Elymus repens was studied for plants collected from Denmark, Finland, Norway and Sweden. At 2‐week intervals from July to October, 5‐cm fragments of roots or rhizomes were cut from plants grown in buckets and planted into soil in pots, half of which were placed immediately into growth chambers at 18°C for 4 weeks. The other half of the pots were initially placed in a dark room at 2°C for 4 weeks before being transferred to the same growth chamber, also for 4 weeks. During the growth chamber period, the numbers of emerged shoots in each pot were counted weekly. The sprouting activity of C. arvense and E. repens was relatively uniform during this period and bud dormancy was not apparent. In all ecotypes of S. arvensis, innate bud dormancy developed during the latter part of the growing season. For all three species, differences in sprouting readiness were found among ecotypes. The results imply that C. arvense and E. repens are more likely to be controlled by mechanical measures in autumn than S. arvensis.     

Importance of timing and repetition of stubble cultivation for post‐harvest control of Elymus repens

Without herbicides, the control of Elymus repens relies on intensive tillage, often in the form of repeated post‐harvest stubble cultivations followed by ploughing. This is costly and time‐consuming and also increases the risk of nitrogen leaching. Our aim was to quantify the controlling effect on E. repens of single and repeated cultivation and differing time of cultivation in relation to spring cereal harvest. A 2‐year experiment was conducted at two sites in the south and east of Sweden in 2011–2012 and 2012–2013. We compared no, single and repeated tine cultivation followed by mouldboard ploughing; the single cultivation was performed directly after harvest or 20 days after harvest; when repeated, the first cultivation was performed immediately or 5 days after harvest, followed by a second cultivation 20 days after harvest. Tine cultivation in combination with mouldboard ploughing resulted in 50–70% lower rhizome biomass, and increased average subsequent cereal yields by 0–130% compared with ploughing alone. Large E. repens populations appeared to be more efficiently reduced by tine cultivation than smaller populations. A single tine cultivation 20 days after harvest tended to result in a higher E. repens shoot density and more rhizome biomass in the subsequent year than tine cultivation directly after harvest. Additional cultivation 20 days after harvest did not improve control of E. repens or the subsequent cereal grain yield, compared with a single cultivation conducted directly after harvest. In conclusion, preventing the growth of E. repens during the early part of the post‐harvest autumn period was more important than starving rhizomes with repeated cultivations.     

EFFECTS OF DECREASING THE LIGHT INTENSITY ON THE GROWTH OF AGROPYRON REPENS (L.) BEAUV. IN THE FIELD

Summary. Small plots of Agropyron repens (L.) Beauv, were shaded with ‘Tygan’ screening fabric which transmitted approximately 46% of daylight. In 1968, plots were either shaded or unshaded throughout the experiment (from mid-May until September) and in 1969, some plots were also shaded early (mid-May to mid-July) or late (mid-July to September). In both experiments continuous shading halved rhizome dry weight but had a much smaller effect on shoot dry weight. It also decreased rhizome dry matter by 5%. With early shading there were fewer shoots and ears until mid-July but this difference disappeared by September, because plants shaded early produced more shoots and ears after mid-July than unshaded plants. Early shading slightly decreased the final percentage of shoots that developed ears. Early shading increased shoot height by mid-July and late shading increased it by the end of the experiment. Effets de la diminution de l'intensié lumineuse sur la croissance de l'Agropyron repens (L.) Beauv, au champ Résumé. De petites parcelles d'Agropyron repens (L.) Beauv. ont été ombragiés avec du ‘Tygan’écran en treillis qui ne laisse passer que 46% environ de la lumère du jour. En 1968, les parcelles furent ombragées ou non pendant toute la durée de l'expérience (de mi-mai à septembre); en 1969 certaines parcelles furent aussi ombragées précocement (de mi-mai à mi-julliet) ou tardivement (de mi-jmllet à septembre). Dans les deux expériences, l'ombrage continu réduisit de moitié le poids sec des rhizomes mais eut un effet beaucoup plus faible sur le poids sec de la partie aérienne. II réduisit également de 5% la matière sèche des rhizomes. Avec un ombrage précoce, il y eut moins de tiges et d'épis jusquà mi-juillet, mais cette différence n'existait plus en septembre paree que les plantes ombragées précocement produisirent après la mi-juillet, plus de tiges et d'épis que les plantes non ombragées. L'ombrage précoce diminua le pourcentage final des tiges qui produisirent des épis. L'ombrage précoce augmenta la hauteur des tiges à la mi-juillet et l'ombrage tardif eut le même effet à la fin de I'expérience. Auswirkungen verringerter Lichtintensität auf das Wachstum von Agropyron repens (L.) Beauv. Im Feld Zusammenfassung. Kleine Parzellen mit Agropyron repens (L.) Beauv. wurden mit ‘Tygan’ Abschirmmaterial, das etwa 46% des Tageslichts durchliess, beschattet. Im Jahre 1968 wurden die Parzellen während der gesamten Versuchadauer (von Mitte Mai bis September) entweder beschattet oder nicht beschattet; 1969 wurden auch einige Parzellen früh (von Mitte Mai bis Mitte Juli) oder spät (von Mittc Juli bis September) beschattet. In beiden Experimenten reduzierte durchgehende Beschattung das Rhizom-trockengewicht um die Hälfte, hatte jedoch eine weit geringere Auswirkung auf das Trockengewicht der oberirdischen Teile. Die Rhizomtrockensubstanz war um 5% vermindert, Bei früher Beschattung würden bis Mitte Juli weniger Schosse und Ahren gebildet; dieser Unterschied war jedoch bis September wieder verschwunden, da beschattete Pflanzen ab Mitte Juli mehr Schosse und Ähren produzierten als unbeschattete. Frühe Besehattung führte zu einer leiehten Verringerung des Prozentsatzes der Schosse, die Ähren bildeten. Die Länge der Sehosse war Mitte Juli durch frühe Beschattung vergrössert und am Ende des Experiments durch späte Besehattung.     

EFFECTS OF LIGHT INTENSITY, PHOTOPERIOD AND NITROGEN ON THE GROWTH OF SEEDLINGS OF AGROPYRON REPENS (L.) BEAUV. AND AGROSTIS GIGANTEA ROTH

Summary. Seeding of Agropyron repens (L.) Beauv. und Agrostis gigantea Roth were grown in two photoperiods and with amounts of nitrogen. On two occasions plants transferred between photoperiods.
The early growth of the seedlings was increased most by increasing the light intensity, but later nitrogen had the greatest effect. In short photoperiods, plants of both species were decumbent and had many more shoots than in long photoperiods. At the end of the experiment, plants of both species responded more to nitrogen in bright than in dim light, and the dry weight of Agropyron was increased more than that of Agrostis by increased photoperiod and nitrogen.
Agropyron initiated rhizomes sooner than Agrostis ; it had fewer rhizomes but they were longer and thicker and weighed more. Brighter light, longer photoperiod and nitrogen all increased rhizome weight. Photoperiod did this mainly by producing more rhizomes, light by increasing thickness or density, and nitrogen by both. The effects of photoperiod and nitrogen on the rhizome dry weight of Agropyron , but not of Agrostis , were additive.
Transferring plants from short to long photoperiods or from long to short, respectively increased or decreased total growth, but had an opposite effect on the rhizomes.     

SPATIAL GROWTH OF CYNODON DACTYLON (L.) PERS.*

Summary. Small sprigs of Cynodon dactylon (L.) Pers., were planted and grown without competition from weeds and crops for 2 1/2 years. The plant spread by means of above-ground creeping stolons and subterranean rhizomes which could also emerge as aerial shoots, producing in their turn new stolons and rhizomes. Initially there was linear extension of stolons and rhizomes, following which gaps in the sod were filled by stolon branching and new shoots. There was no preferential direction of stolon elongation and established sods developed an approximately circular shape and expanded concentrically. The rate of increase in sod area was similar in both years of observation but radial extension was smaller in the second year than in young plants. The mean sod area was 25 m² after 2½ years of growth, and mean monthly area increment was 0·9 m². Growth almost stopped in the cold season and exceeded 2 m² per month in the summer. The plants had extended up to 3·9 m from the plant centre after 2 1/2 years. The number of flowering culms per sod, produced only in the warm season, was directly proportional to sod area; seeds were infertile in the Newe Ya'ar area. After 2½ years of growth about 70% of the rhizome dry weight was present in the upper 20 cm of soil. Few rhizomes penetrated deeper than 40 cm. More than 60% of the rhizomes were present within 1 m radius of the plant centre and 90% were present within 2 m radius. Croissance spatiale de Cynodon dactylon (L.) Pers.     

Rhizome dynamics in Calystegia japonica Choisy and Calystegia hederacea Wall. in relation to overwintering

Calystegia japonica Choisy and Calystegia hederacea Wall., common perennial weeds throughout cropped and uncropped land in Japan, are known to regenerate mostly by rhizomes. The rhizome dynamics of the two species were investigated, focusing on their overwintering characteristics. The dry weight of rhizomes continued to increase for 6–7 weeks after the decrease in weight of the aerial parts began, then it decreased in winter because of the partial death and consequent fragmentation of the rhizomes. Overwintering as naturally fragmented rhizomes is a unique characteristic of the two Calystegia spp. as it is not observed in other rhizomatous weeds that maintain systematic connections at least during the following regeneration in spring. In C. japonica , rhizome degradation was more pronounced and more systematic than in C. hederacea , where thicker fragments that included apices remained. Qualitative changes in C. japonica rhizomes, such as increases in dry matter accumulation and starch, and a temporary decrease in sprouting ability, seem to relate to this specialized survival mechanism. Calystegia hederacea did not show either specialization or preparation for overwintering in its rhizome. The adaptability of Calystegia weeds to annual crop fields can be attributed to their capacity to regenerate from naturally fragmented rhizomes.