Winter Annuals Research Articles

Crop Analysis through Growth Survey after Wintering of Winter Annual Forages Grown from 2014 to 2015

ABSTRACT In order to identify the causes of various problems related to forage crop growth, such as winter survival, coldness, rainfall, drought etc., and to provide basic data for the stable production and supply of forage year round, we performed a growth survey after the wintering of winter forage crops grown from mid-Sep. 2014 to late-Feb. 2015. The growth of winter forage crops after wintering in the country was generally bad. As shown in the regional distribution in the country, regions with 80% or higher winter survival rates comprised 66%, regions with 79 to 50% winter survival comprised 24.9% and regions with less than 50% winter survival comprised 9.1%. In conclusion, the average winter survival rate was 79% in the country. Winter survival rate and coverage rate after the wintering of winter forage crops under installed drain channels in paddy fields were good at 83% and 80%, respectively. However, the rates without installed drain channels were bad at 67% and 66%, respectively. It was predicted that the crop production of winter forage crops was reduced by 10-15% in Gangwon, Chungbuk, Chungnam, Gyeongnam and Jeonnam regions, reduced by 30% in Gyeonggi, Gyeongbuk and Jeonbuk regions and reduced overall by approximately 19% nationwide.(

제주도 밭의 외래잡초 분포

We surveyed the distribution of exotic weeds in the 141 crop fields of Jeju island. The exotic weeds were summarized as 66 taxa including 18 families, 50 genera, 64 species and 2 varieties. In winter crop fields there were 45 species of exotic seeds in 18 families, in summer crop fields 50 species in 16 families, and in perennial crop fields 39 species in 17 families. Total exotic weeds were classified to 39.4% of summer annuals, 36.4% of winter annuals, 7.6% of summer and winter annuals, and 16.7% of perennials. The ratio of summer annuals were high in the summer crop fields. Compositae was dominant family, followed by Gramineae, Malvaceae and Solanaceae. Malvaceae did not appear in perennial crop fields. Dominant exotic weeds in winter crop fields were Chenopodium album, Amaranthus viridis, Senecio vulgaris and Coronopus didymus, in summer crop fields, Chenopodium album, Amaranthus viridis, Senecio vulgaris and Sonchus oleraceus and in perennial crop fields, Conyza sumatrensis, Gnaphalium calviceps and Senecio vulgaris. The dominant exotic weeds in the crop fields of Jeju island were Chenopodium album, followed by Amaranthus viridis, Senecio vulgaris, and Conyza sumatrensis. This information could be useful for establishment of exotic weed control methods in Jeju island.

Variation in Life History Traits ofGentiana nivalis(Gentianaceae) in Alpine and Sub-Alpine Habitats in the Norwegian Mountains and Its Implications for Biodiversity in Relation to Environmental Change

The alpine gentian, Gentiana nivalis, is an obligate annual. Because of its complete population turnover every year, it is likely to be more responsive to environmental shifts than are perennials, and also likely to undergo more rapid genetic change in response to selection pressure. The detected morphological differentiation between habitats was related to different proportions of spring- and autumn-germinating individuals with a larger proportion of winter annuals in the subalpine habitats. The spring-germinating annuals that have shorter time for development and have a shorter stature can still develop at the alpine sites where competition is weaker. The subalpine habitats are all semi-natural, shaped by livestock grazing and human activities related to summer farming. Declining human impact is leading to successional changes in the mountain landscape. The future of G. nivalis in the light of current trends in landscape development and climate change is discussed.

Effects of precipitation change and neighboring plants on population dynamics of Bromus tectorum.

Shifting precipitation patterns resulting from global climate change will influence the success of invasive plant species. In the Front Range of Colorado, Bromus tectorum (cheatgrass) and other non-native winter annuals have invaded grassland communities and are becoming more abundant. As the global climate warms, more precipitation may fall as rain rather than snow in winter, and an increase in winter rain could benefit early-growing winter annuals, such as B. tectorum, to the detriment of native species. In this study we measured the effects of simulated changes in seasonal precipitation and presence of other plant species on population growth of B. tectorum in a grassland ecosystem near Boulder, Colorado, USA. We also performed elasticity analyses to identify life transitions that were most sensitive to precipitation differences. In both study years, population growth rates were highest for B. tectorum growing in treatments receiving supplemental winter precipitation and lowest for those receiving the summer drought treatment. Survival of seedlings to flowering and seed production contributed most to population growth in all treatments. Biomass of neighboring native plants was positively correlated with reduced population growth rates of B. tectorum. However, exotic plant biomass had no effect on population growth rates. This study demonstrates how interacting effects of climate change and presence of native plants can influence the population growth of an invasive species. Overall, our results suggest that B. tectorum will become more invasive in grasslands if the seasonality of precipitation shifts towards wetter winters and allows B. tectorum to grow when competition from native species is low.

Seedbank and Field Emergence of Weeds in Glyphosate-Resistant Cropping Systems in the United States

A segment of the debate surrounding the commercialization and use of glyphosate-resistant (GR) crops focuses on the theory that the implementation of these traits is an extension of the intensification of agriculture that will further erode the biodiversity of agricultural landscapes. A large field-scale study was initiated in 2006 in the United States on 156 different field sites with a minimum 3-yr history of GR-corn, -cotton or -soybean in the cropping system. The impact of cropping system, crop rotation, frequency of using the GR crop trait, and several categorical variables on seedbank weed population density and diversity was analyzed. The parameters of total weed population density of all species in the seedbank, species richness, Shannon's H′ and evenness were not affected by any management treatment. The similarity between the seedbank and aboveground weed community was more strongly related to location than management; previous year's crops and cropping systems were also important while GR trait rotation was not. The composition of the weed flora was more strongly related to location (geography) than any other parameter. The diversity of weed flora in agricultural sites with a history of GR crop production can be influenced by several factors relating to the specific method in which the GR trait is integrated (cropping system, crop rotation, GR trait rotation), the specific weed species, and the geographical location. Continuous GR crop, compared to fields with other cropping systems, only had greater species diversity (species richness) of some life forms, i.e., biennials, winter annuals, and prostrate weeds. Overall diversity was related to geography and not cropping system. These results justify further research to clarify the complexities of crops grown with herbicide-resistance traits to provide a more complete characterization of their culture and local adaptation to the weed seedbank.

Overwintering Sites ofIris yellow spot virusandThrips tabaci(Thysanoptera: Thripidae) in Colorado

Iris yellow spot virus (family Bunyaviridae, genus Tospovirus) and its insect vector, onion thrips, Thrips tabaci Lindeman, are of economic concern worldwide in regions where onions (Allium cepa L.) are grown. Several weed species have been described as additional hosts and likely green bridges for survival of Iris yellow spot virus, however, there is little work regarding the overwintering habits and potential of onion thrips as a source of inoculum during the following season. The results of this work confirm onion thrips and Iris yellow spot virus presence near three Colorado onion fields throughout the winter, onion thrips reproduction on six non-allium plant species, and larval acquisition of Iris yellow spot virus from two non-allium plant species. Thrips were monitored by sticky traps during the winter months from 2011 to 2013. Thrips activity seemed to cease when the average temperature was cooler than 0°C and resumed once the average temperature warmed above 0°C. Onion cull piles were constructed and were apparently conducive to survival of thrips, but no live thrips were collected from the piles after onion bulbs began to decay. Iris yellow spot virus was detected by RTPCR in live adult and larval thrips from onion; common mallow, Malva neglecta Wallr.; dandelion, Taraxacum officinale Weber in Wiggers; flixweed, Descurainia sophia (L.) Webb. Ex Prantl; prickly lettuce, Lactuca serriola L.; and salsify, Tragopogon dubius Scop. during the winters from 2010 to 2013. Iris yellow spot virus was detected in prickly lettuce and flixweed. The five weed species were grown from seed in a greenhouse and exposed to viruliferous thrips to elucidate their potential as green bridges. Of the five weeds, Iris yellow spot virus was detected in eight of 15 salsify leaf samples and in three of six thrips larval samples reared on the plant. Winter annuals play a role in overwintering survival of onion thrips and Iris yellow spot virus, providing inoculum the next growing season, and weed management during the winter might be warranted.

Flowering time and seed dormancy control use external coincidence to generate life history strategy.

Climate change is accelerating plant developmental transitions coordinated with the seasons in temperate environments. To understand the importance of these timing advances for a stable life history strategy, we constructed a full life cycle model of Arabidopsis thaliana. Modelling and field data reveal that a cryptic function of flowering time control is to limit seed set of winter annuals to an ambient temperature window which coincides with a temperature-sensitive switch in seed dormancy state. This coincidence is predicted to be conserved independent of climate at the expense of flowering date, suggesting that temperature control of flowering time has evolved to constrain seed set environment and therefore frequency of dormant and non-dormant seed states. We show that late flowering can disrupt this bet-hedging germination strategy. Our analysis shows that life history modelling can reveal hidden fitness constraints and identify non-obvious selection pressures as emergent features.

Dormancy in cereals (not too much, not so little): about the mechanisms behind this trait

AbstractAs in other cultivated species, dormancy can be seen as a problem in cereal production, either due to its short duration or to its long persistence. Indeed, cereal crops lacking enough dormancy at harvest can be exposed to pre-harvest sprouting damage, while a long-lasting dormancy can interfere with processes that rely on rapid germination, such as malting or the emergence of a uniform crop. Because the ancestors of cereal species evolved under very diverse environments worldwide, different mechanisms have arisen as a way of sensing an appropriate germination environment (a crucial factor for winter or summer annuals such as cereals). In addition, different species (and even different varieties within the same species) display diverse grain morphology, allowing some structures to impose dormancy in some cereals but not in others. As in seeds from many other species, the antagonism between the plant hormones abscisic acid and gibberellins is instrumental in cereal grains for the inception, expression, release and re-induction of dormancy. However, the way in which this antagonism operates is different for the various species and involves different molecular steps as regulatory sites. Environmental signals (i.e. temperature, light quality and quantity, oxygen levels) can modulate this hormonal control of dormancy differently, depending on the species. The practical implications of knowledge accumulated in this field are discussed.

Winter Annual Weed Response to Nitrogen Sources and Application Timings prior to a Burndown Corn Herbicide

Autumn and early preplant N applications, sources, and placement may affect winter annual weed growth. Field research evaluated (1) the effect of different nitrogen sources in autumn and early preplant on total winter annual weed growth (2006–2010), and (2) strip-till and broadcast no-till N applied in autumn and early preplant on henbit (Lamium amplexicauleL.) growth (2008–2010) prior to a burndown herbicide application. Total winter annual weed biomass was greater than the nontreated control when applying certain N sources in autumn or early preplant for no-till corn. Anhydrous ammonia had the lowest average weed density (95 weeds m−2), though results were inconsistent over the years. Winter annual weed biomass was lowest (43 g m−2) when applying 32% urea ammonium nitrate in autumn and was similar to applying anhydrous ammonia in autumn or early preplant and the nontreated control. Henbit biomass was 28% greater when applying N in the autumn compared to an early preplant application timing. Nitrogen placement along with associated tillage with strip-till placement was important in reducing henbit biomass. Nitrogen source selection, application timing, and placement affected the impact of N on winter annual weed growth and should be considered when recommending a burndown herbicide application timing.

2014年映像情報メディア学会冬季大会

2014年映像情報メディア学会冬季大会

경기도 밭의 외래잡초 분포

We surveyed the distribution of exotic weeds in the 350 upland crop fields of Gyeonggi-do. The exotic weeds were summarized as 78 taxa including 19 families, 52 genera, 74 species and 4 varieties. Among the total exotic weeds, the summer annuals were 48.7%, the winter annuals 28.2%, and the perennials 23.1%. Compositae was dominant family (32%), followed by Gramineae (8%), Polygonaceae (8%) and Malvaceae (7%). Dominant exotic weeds in northern Gyeonggi-do were Amaranthus lividus, Ambrosia trifida, Chenopodium album, Bidens frondosa and Erigeron Canadensis, and in southern Gyeonggi-do were Chenopodium album, Erigeron Canadensis, Erigeron annuus, Taraxacum officinale and Galinsoga ciliate. The most dominant exotic weeds in the Gyeonggi-do were Chenopodium album, followed by Amaranthus blitum, Erigeron canadensis. Canonical correspondence analysis for investigation of correlation between exotic weeds occurred in northern and southern Gyeonggi-do showed that the exotic weeds in northern Gyeonggi-do were more diverse then in southern Gyeonggi-do. This information could be useful for establishment of exotic weed control methods in Gyeonggi-do.

Plant community – soil relationships in a topographically diverse grassland in southern interior British Columbia, Canada

The current management focus for many of British Columbia’s grasslands is on sustaining their high natural and economic values in light of concerns over climate change and spread of exotic species. To that end, scientific information on plant community – soil – topographic relationships is required to assist with the often complex decisions that managers face. We collected data on vegetation, topography, and soil properties at 38 sites over a range of elevation zones and aspects at Lac du Bois Grasslands Provincial Park near Kamloops, British Columbia. Cluster analysis of the vegetation data validated the current three-zonal system used for grazing management but indicated that boundaries between adjacent plant communities are interspersed according to aspect. Principal component analysis (PCA) of environmental variables identified a gradient from the less productive, lower grasslands (higher soil bulk density, bare soil, coarse fragment content), to the more productive, upper grasslands (higher litter cover, total soil C and aggregate stability). Projection of six exotic species functional groups into the PCA-environment space showed significant associations of winter annuals with the lower grasslands, versus perennials (both clonal reproducers and seed bankers) with the upper grasslands. Our analysis showed promise in identifying fine-scale linkages between plant community patterns and key environmental factors. This approach may be useful as part of a proactive management plan for maintaining the health of British Columbia grasslands.

Effects of Seedling Emergence Timing on the Population Dynamics of Horseweed (Conyza canadensisvar.canadensis)

Horseweed is a surface-germinating ruderal facultative winter annual. The ruderal nature is a key adaptive characteristic that implicates emergence timing as an important recruitment factor. Experiments were established at three sites in southern Ontario, Canada, from 2009 to 2012 to determine the possible effect of emergence timing of horseweed on plant number, fecundity, and flowering timing. Emerged seedlings were tagged in 0.25-m2plots in five 2-wk cohorts in the fall and spring of each experimental season. Each plot was followed though until the plants contained within each plot completed their life cycle. Generally, spring-emerging plants were found to flower earlier than fall-emerging plants, but with fall emergence there were higher plant densities in August each season compared with spring emergence. Overall, there was no difference in fecundity between spring- or fall-emerging cohorts, but when cohorts were parsed beyond just spring or fall emergence, we found that plants emerging in early fall and early spring were more fecund and flowered earlier than plants emerging in late fall and late spring. Disturbance (tilled versus not-tilled) significantly affected emergence levels but not emergence timing. The differences in performance among emergence cohorts are likely due to spatial or temporal density-dependent growth advantages. These results show that spring-emerging cohorts of horseweed, especially early spring–emerging cohorts, should not be discounted when considering the weediness of this species, and this may hold true for other facultative winter annual weeds as well.

Characterization of Fragaria virginiana and F. chiloensis in a Minimal-chill, Winter Annual Production System

Wild Fragaria supercore accessions from the U.S. Department of Agriculture (USDA) National Plant Germplasm System collection have been evaluated in temperate climates; however, there have been no characterizations of supercore accessions in non-temperate climates or in annualized production systems. Because Florida can serve as a model system for annualized winter and spring production worldwide, the objective of this study was to characterize an elite group of wild strawberry accessions under field and high tunnel production systems for mortality and the phenological responses of flowering and runner production. The wild accessions along with cultivars were planted in open-field and high tunnel production environments in a randomized complete block design within each environment with raised beds serving as blocks. Four replications of five-plant plots were planted in each of two environments in 2 separate years. With the exception of Darrow 72, F. chiloensis accessions did not perform well in the minimum-chill annualized winter production system. The accessions of this species generally did not flower and were prolific instead in runner production. The F. virginiana accessions performed better with F. virginiana subsps. grayana and virginiana accessions appearing more adapted for minimum-chill winter production because they flowered well and had few runners. We conclude that NC 96-48-1 (PI 612324), NC 95-21-1 (PI 612569), Darrow 72 (PI 236579), and RH 30 (PI 612499) would be attractive for inclusion in germplasm development in a minimal-chill, winter annual production system. In addition to producing many flowers and few runners, these accessions had low mortality.

Violet Biology and Management in Turf

Violets (Viola spp.) are diverse winter annuals and perennials. Perennials form rhizomes or long stolons. Many have heart-shaped leaves on long petioles and have a rosette growth habit. Some have linear leaves and others have palmate leaves. Flowers are generally purple, but can be white, pink or yellow. They reproduce by seed or, when produced, rhizomes. This 2-page fact sheet was written by Darcy E. P. Telenko, Barry J. Brecke, Ramon Leon, and J. Bryan Unruh, and published by the UF Department of Environmental Horticulture, December 2013.
 ENH1235/EP496: Violet Biology and Management in Turf (ufl.edu)

Application time and herbicide rate effects on weeds in oilseed rape (Brassica napus var. oleifera)

Field trials were conducted in 2010 and 2011 to evaluate different application time of metazachlor (Butisan 400 SC) and dimethachlor (Teridox-500), and their rate effects on weeds in oilseed rape (OSR). The weed population was consisted of winter and summer annuals, some perennial weeds, and volunteer wheat. Veronica spp., Triticum aestivum, Camelina sativa and Alopecurus myosuroides infestations were heavy throughout the experimental areas in both years. Efficacy of PRE herbicides was lower in comparison with early POST herbicides; it was ranged from 77.8% (Teridox – 2.0 L/ha) in Bitola locality to 86.9% (Butisan – 3.5 L/ha) in Skopje locality. Efficacy of early POST herbicides was ranged from 88.3% (Teridox – 2.0 L/ha) in Bitola locality to 98.6% (Butisan – 3.5 L/ha) in Skopje locality. Control of prevailing weeds was ranged from 53% to 97%, and 66% to 100% with PRE and early POST herbicide treatments, respectively. Particularly high efficacy showed Butisan applied early POST at 2.5 and 3.5 L/ha, respectively which excellent controlled prevailing weeds in both localities. All applied herbicides showed high selectivity to OSR; no visual injuries were determined by any rates in both years. OSR grain yield of herbicides applied PRE was lower in comparison with their early POST application.

Henbit (Lamium amplexicaule), Common Chickweed (Stellaria media), Shepherd's-Purse (Capsella bursa-pastoris), and Field Pennycress (Thlaspi arvense): Fecundity, Seed Dispersal, Dormancy, and Emergence

Winter annual weeds protect the soil from erosion and retain nutrients during the winter; however, they can also act as a host for crop pests and pathogens and impede planting. Increased knowledge of the reproductive biology and the seed fate of winter annuals would be useful to improve management and crop productivity. The objectives of this research were to determine the recruitment biology of shepherd's-purse, henbit, common chickweed, and field pennycress, including seed production, dispersal, dormancy, and seedling emergence, based on growing degree days (GDD). Henbit was the least prolific of the four weeds studied, producing 800 to 40,000 seeds m−2at naturally occurring densities; shepherd's-purse was the most prolific, producing 11,000 to 400,000 seeds m−2with 40 to 230 plants m−2. Fifty percent seed rain occurred for henbit, common chickweed, shepherd's-purse, and field pennycress at 620, 790, 880, and 1300 GDDBase,0C, respectively. Overall, seeds were dormant for all species at the time of dispersal. In 2 of 3 yr, dormancy of later-dispersed common chickweed decreased after 6 mo of storage at natural, fluctuating temperatures in the absence of water. The emergence patterns of the four species followed the Gompertz equation and were indicative of facultative winter annuals. The emergence patterns by rate were similar between henbit and common chickweed and between shepherd's-purse and field pennycress. Seed production, dispersal, dormancy, and seedling emergence were influenced by moisture; therefore, including a precipitation or soil moisture component into a GDD model (such as the use of hydrothermal time) would improve the accuracy of predicting winter annual reproduction, seed fate, and emergence.

Growth Stage Affects Response of Selected Weed Species to Flaming

Propane flaming could be an alternative tool for PRE control or suppression of early-emerging weeds in organic and conventional crops. The objective of this study was to test the tolerance of selected early-season weeds to broadcast flaming in no-till systems. Four winter annuals (tansy mustard, henbit, cutleaf evening primrose, and field pennycress), one summer annual (common lambsquarters), and one perennial (dandelion) species were included in the study. Except for dandelion, the response to propane flaming was evaluated at two growth stages. Flaming treatments were applied using an all-terrain-vehicle-mounted flamer moving 4.8 km h−1, and propane pressure was adjusted to deliver doses of 0 (nonflamed control), 22, 34, 48, 67, and 90 kg ha−1. The response of each species to propane doses was described by log-logistic models based on visual ratings of weed control and dry matter reduction. Response to broadcast flaming varied among species and growth stages. Common lambsquarters, tansy mustard, and henbit were more susceptible to flaming than cutleaf evening primrose, field pennycress, and dandelion. On the basis of visual ratings, propane doses between 54 and 62 kg ha−1 effectively controlled (90% control) common lambsquarters at the early growth stage (five-leaf), tansy mustard at both growth stages (nine-leaf and flowering), and henbit (flowering). However, a higher propane dose (> 80 kg ha−1) was necessary to obtain 90% control of common lambsquarters in later growth stage (11-leaf) and early growth stage of henbit (nine-leaf). Cutleaf evening primrose, field pennycress, and dandelion exhibited higher levels of tolerance to broadcast flaming. A 90% control of these species was not achieved even with the highest propane dose (90 kg ha−1) utilized in the study. Results of this study indicate that a single application of broadcast flaming can be an effective tool for controlling tansy mustard, henbit, and common lambsquarters and temporary suppression of cutleaf evening primrose, field pennycress, and dandelion.

Environmental Triggers of Winter Annual Weed Emergence in the Midwestern United States

Winter annual weeds are becoming prolific in agricultural fields in the midwestern United States. The objectives of this research were to understand the roles of soil temperature (daily average and fluctuation) and moisture on the emergence of nine winter annual weed species and dandelion and to develop predictive models for weed emergence based on the accumulation of modified thermal/hydrothermal time (mHTT). Experiments were established at Lincoln, NE; Mead, NE; and at two sites (irrigated and rainfed) near Clay Center, NE, in 2010 and 2011. In July of each year, 1,000 seeds of each species were planted in 15 by 20 by 6-cm mesh baskets installed between soybean rows. Soil temperature and water content were recorded at the 2-cm depth. Emerged seedlings were counted and removed from the baskets on a weekly basis until no additional emergence was observed in the fall, resumed in late winter, and continued until emergence ceased in late spring. Weather data were used to accumulatemHTT beginning on August 1. A Weibull function was selected to fit cumulative emergence (%) on cumulativemHTT (seven base temperature [Tbase] by six base water potential [Ψbase] by three base temperature fluctuation [Fbase] candidate threshold values = 126 models); it was also fit to days after August 1 (DAA1), for a total of 127 candidate models per species. The search for optimal base thresholds was based on the theoretic-model comparison approach (Akaike information criterion [AIC]). All three components (Tbase, Ψbase, andFbase) were only important for Virginia pepperweed. For downy brome and purslane speedwell, includingTbaseand Ψbaseresulted in the best fit, whereas for dandelion includingTbaseandFbaseresulted in the best fit. A model including onlyTbaseresulted in the best fit for most species included in this study (Carolina foxtail, shepherd's-purse, pinnate tansymustard, henbit, and field pansy). For field pennycress, the model based on DAA1 resulted in the best fit. Threshold values were species specific. Soil temperature was the major environmental factor influencing winter annual weed emergence. Even though soil moisture and often temperature fluctuation are essential for seed germination, ΨbaseandFbasewere not as critical in the predictive models as initially expected. Most seedlings (> 90%) of downy brome, pinnate tansymustard, Carolina foxtail, henbit, and field pansy emerged during the fall. Virginia pepperweed, purslane speedwell, dandelion, shepherd's-purse, and field pennycress seedlings emerged during both fall and spring. The results of this research provide robust information on the prediction of the time of winter annual weed emergence, which can help growers make better management decisions.

The relationship between vernalization saturation and the maintenance of freezing tolerance in winter rapeseed

Vernalization requirement maintains winter annuals in a cold hardy vegetative state during the winter. Vernalization saturation has been shown to be followed by a loss of freezing tolerance under controlled experimental conditions. The objective of this study was to determine a possible relationship between vernalization saturation and the maintenance of cultivar specific freezing tolerance levels in winter rapeseed (Brassica napus L.) under field conditions. Two cultivars, ‘Banjo’ and ‘Californium’, with differing vernalization requirements were chosen after a screening of 18 cultivars under controlled conditions. Vernalization response and freezing tolerance of the two cultivars grown under field conditions were compared on five different dates throughout the winter of 2010/11 at Apelsvoll Research Station, Norway (60° 42′ N, 10° 52′ E, 250m a.s.l.). ‘Californium’ reached vernalization saturation on 11 Oct. whereas ‘Banjo’ did 13 days later. Maximum freezing tolerance of both cultivars was attained in early December and it was maintained for 31 days in ‘Californium’ and 67 days in ‘Banjo’. Our results indicate that there is no simple relationship between freezing tolerance and saturation of vernalization. Increasing contents of water, d-glucose and d-fructose and decreasing sucrose and starch levels in the shoot apex from mid to late winter were significantly correlated with a decrease in freezing tolerance (LT50) and shoot regrowth following a −12°C low temperature treatment and so these parameters may be good predictors of plant survival and vitality in the spring.