Relationships between phoma leaf spot and development of stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus) in southern England

Models were constructed to describe the relationships between incidence of phoma leaf spot at different growth stages in autumn/winter or early spring and incidence of stem canker (basal canker or stem lesions) in summer on winter oilseed rape in southern England. Model 1, describing the phoma leaf spot/basal canker relationship, was y₁=β₀+β₁x₁+β₂(x₂ ‐ x₁) if x₂ > x₁, and y₁=β₀+β₁x₁ if x₂≤x₁, in which y₁ was the incidence (% plants affected) of basal canker at harvest, x₁ was the maximum incidence of phoma leaf spot during the period from sowing to growth stage (G.S.) 1,6‐1,7 (about 100 days after sowing) and x₂ was the maximum incidence of phoma leaf spot between G.S. 1,7 and G.S. 2,0 (start of stem extension). Model 2, describing the phoma leaf spot/stem lesion relationship, was y₂=α₀+α₁x₃+α₂x₄, in which y₂ was the incidence of stem lesions at harvest, x₃ was the incidence of phoma leaf spot at G.S. 3,3–3,5 (flower buds visible) and x₄ was the incidence of phoma leaf spot at G.S. 4,5–5,5 (flower buds opening). Data from field experiments with four winter oilseed rape cultivars at Boxworth or Rothamsted in the 1992/93, 1993/94, 1996/97, 1997/98 or 1998/99 seasons were used to test the models. The values of R² for the regression equations testing model 1 for the phoma leaf spot/basal canker relationship were 0.75, 0.93, 0.91 and 0.89 for cvs Apex, Bristol, Capitol and Envol, respectively. The values of R² for the regression equations testing model 2 for the phoma leaf spot/stem lesion relationship were 0.58, 0.57, 0.54 and 0.71 for cvs Apex, Bristol, Capitol and Envol, respectively. The phoma leaf spot/basal canker relationship (model 1) could also be fitted to the combined data set for all four cultivars (R²= 0.65), whereas the phoma leaf spot/stem lesion relationship (model 2) could not to be fitted to the combined data set for the four cultivars. The relationships between incidence and severity of stem canker were examined and the values of R² for the regressions of severity on incidence were 0.91 for basal canker and 0.89 for stem lesions.     

Autumn sowing increases severity of pasmo (Mycosphaerella linicola) on linseed in the UK

Surveys and field experiments showed pasmo to be the most serious disease affecting UK winter linseed in the 1997–98, 1998–99 and 1999–2000 growing seasons. Survey data indicated that pasmo was widespread in England and Scotland, causing extensive loss of leaves and stem and capsule symptoms, on both winter and spring linseed crops. In winter linseed experiments at ADAS Boxworth and Rothamsted, when severe epidemics occurred (1997–98 and 1999–2000), control of pasmo with one or two MBC fungicide sprays increased yield. In experiments when severe pasmo epidemics did not occur (1998–99), fungicide applications did not increase yield. In all three growing seasons, large numbers of air-borne Mycosphaerella linicola ascospores were collected in the summer months. At the time when the winter linseed crop was emerging and becoming established in October/November, there were more air-borne M. linicola ascospores in 1999 than in 1998. April/May rainfall was much greater in 1998 (135 mm) and 2000 (223 mm), when severe pasmo epidemics developed by July, than in 1999 (68 mm) when disease severity in July was less. Regression analyses suggested that yield decreased as percentage area affected by pasmo on leaves or stems in July increased. The formulae relating yield loss to pasmo severity, derived from these experiments, were combined with disease survey data to estimate, retrospectively, the UK national losses from pasmo. Estimated national losses from pasmo on winter linseed, although >50% of crops were sprayed with fungicide, were approximately £2.9M in 1998, £1.6M in 1999 and £0.37M in 2000 (when the area of winter linseed had decreased greatly). Estimated combined losses on winter and spring linseed were approximately £14.8M in 1998, £34.9M in 1999 and £11.0M in 2000.     

Analysis of leaf appearance,leaf death and phoma leaf spot,caused by Leptosphaeria maculans,on oilseed rape (Brassica napus) cultivars

Development of phoma leaf spot (caused by Leptosphaeria maculans) on winter oilseed rape (canola, Brassica napus) was assessed in two experiments at Rothamsted in successive years (2003–04 and 2004–05 growing seasons). Both experiments compared oilseed rape cultivars Eurol, Darmor, Canberra and Lipton, which differ in their resistance to L. maculans. Data were analysed to describe disease development in terms of increasing numbers of leaves affected over thermal time from sowing. The cultivars showed similar patterns of leaf spot development in the 2003–04 experiment when inoculum concentration was relatively low (up to 133 ascospores m⁻³ air), Darmor developing 5.3 diseased leaves per plant by 5 May 2004, Canberra 6.6, Eurol 6.8 and Lipton 7.5. Inoculum concentration was up to sevenfold greater in 2004–05, with Eurol and Darmor developing 2.4 diseased leaves per plant by 16 February 2005, whereas Lipton and Canberra developed 2.8 and 3.0 diseased leaves, respectively. Based on three defined periods of crop development, a piece-wise linear statistical model was applied to the progress of the leaf spot disease (cumulative diseased leaves) in relation to appearance (‘birth’) and death of leaves for individual plants of each cultivar. Estimates of the thermal time from sowing until appearance of the first leaf or death of the first leaf, the rate of increase in number of diseased leaves and the area under the disease progress line (AUDPL) for the first time period were made. In 2004–05, Canberra (1025 leaves ×°C days) and Lipton (879) had greater AUDPL values than Eurol (427) and Darmor (598). For Darmor and Lipton, the severity of leaf spotting could be related to the severity of stem canker at harvest. Eurol had less leaf spotting but severe stem canker, whereas Canberra had more leaf spotting but less severe canker.     

Epidemiology of Leptosphaeria maculans in relation to forecasting stem canker severity on winter oilseed rape in the UK

In the UK, ascospores of Leptosphaeria maculans first infect leaves of oilseed rape in the autumn to cause phoma leaf spots, from which the fungus can grow to cause stem cankers in the spring. Yield losses due to early senescence and lodging result if the stem cankers become severe before harvest. The risk of severe stem canker epidemics needs to be forecast in the autumn when the pathogen is still in the leaves, since early infections cause the greatest yield losses and fungicides have limited curative activity. Currently, the most effective way to forecast severe stem canker is to monitor the onset of phoma leaf spotting in winter oilseed rape crops, although this does not allow much time in which to apply a fungicide. Early warnings of risks of severe stem canker epidemics could be provided at the beginning of the season through regional forecasts based on disease survey and weather data, with options for input of crop-specific information and for updating forecasts during the winter. The accuracy of such forecasts could be improved by including factors relating to the maturation of ascospores in pseudothecia, the release of ascospores and the occurrence of infection conditions, as they affect the onset, intensity and duration of the phoma leaf spotting phase. Accurate forecasting of severe stem canker epidemics can improve disease control and optimise fungicide use.     

First Record of Bacterial Canker (Clavibacter michiganensis ssp. michiganensis) on Tomato in Cyprus

Symptoms of bacterial canker disease on tomato were first observed in June 1998, in three tomato fields in the semi‐mountainous region of Eptagonia (Limassol district). In two of these fields, which were planted with cv. FA 179, infection was almost 100%, with heavy losses. The third field, planted with cv. Graziella, had only sporadic infections. An extensive survey during 1998–99 detected 10 additional cases of bacterial canker, all in the wider agro‐ecological zone of initial disease detection. The pathogen Clavibacter michiganensis. ssp. michiganensis was consistently isolated from diseased plants, identified, and its pathogenicity proved. This is the first report of bacterial canker disease on tomato in Cyprus.     

Effects of foliar applications of fungicides during plant growth on grain development and grain germinability in spring barley

In 1990 and 1991 grain samples of spring barley were obtained from plots in which fungal diseases were controlled until ear emergence using fungicide sprays, and from comparable plots which had received no fungicide applications. The grain was stored at 10^oC, and tested for germination at intervals during storage. Grain from plots treated with fungicide consistently exhibited more dormancy than grain from untreated plots. In 1992, grain development was monitored from anthesis to harvest-ripeness in treated and untreated plots of cvs Blenheim, Camargue and Tyne. In cvs Blenheim and Camargue, grains in fungicide-treated plots had a greater dry weight at harvest-ripeness, and dehydrated later in development than grains in untreated plots. Neither of these differences was observed in cv. Tyne. Possible interpretations of the effects of fungicide treatment of the parent plant on the physiology of the grain are discussed.     

Effects of temperature and rainfall on date of release of ascospores of Leptosphaeria maculans (phoma stem canker) from winter oilseed rape (Brassica napus) debris in the UK

Data from a controlled environment experiment investigating effects of temperature on maturation of Leptosphaeria maculans pseudothecia were used to derive equations describing the times until 30% or 50% of pseudothecia were mature as a function of temperature. A wetness sensor was developed to estimate the oilseed rape debris wetness and operated with debris exposed in natural conditions in 2000 and 2001. The maturation of L. maculans pseudothecia on debris and concentrations of airborne L. maculans ascospores were observed from 1999 to 2004. There were considerable differences between years, with the first mature pseudothecia observed in September in most years. There were linear relationships between the first date when 10% of maximum ascospore release was observed and the dates when 30% or 50% of pseudothecia were mature. By summing the daily temperature‐dependent rate of pseudothecial maturation for days after 1 August with rainfall >0.5 mm, the dates when 30% or 50% of pseudothecia were mature were predicted. There was good agreement between predicted and observed dates when 30% or 50% of pseudothecia were mature. These equations for predicting the timing of L. maculans ascospore release could be incorporated into schemes for forecasting, in autumn, the severity of phoma stem canker epidemics in the following spring/summer in the UK.     

Seasonal dispersal patterns of Frankliniella fusca (Thysanoptera: Thripidae) and tomato spotted wilt virus occurrence in central and eastern North Carolina

The seasonal abundance and temporal pattern of Frankliniella fusca Hinds dispersal were monitored from 1996 to 2000 at 12 locations in central and eastern North Carolina. The predominant vector species of tomato spotted wilt virus (TSWV) captured across all locations was F. fusca (98%). The temporal patterns of F. fusca dispersal observed during spring seasons varied among locations in all years except 2000. Regression analysis estimated that times of first flight in the spring seasons varied among locations, whereas flight duration intervals were similar. Temporal patterns of F. fusca captured varied significantly between aerial traps placed 0.1 and 1.0 m above the soil surface. Fewer total thrips were captured at 0.1 m, although thrips dispersal occurred earlier and over a greater time interval compared with 1.0-m traps. Temporal patterns of TSWV occurrence differed among locations in the spring seasons of 1999 and 2000, whereas patterns of virus occurrence were similar during the fall seasons. Patterns of F. filsca dispersal and subsequent TSWV occurrence were synchronous at locations in 1999 and 2000 where the greatest number of TSWV lesions was recorded. Knowledge of the temporal patterns of F. fiasca dispersal and TSWV occurrence may be a useful indicator for describing the time when susceptible crops are at highest risk of TSWV infection.     

Susceptibility of eight potato cultivars to tuber infection by Phytophthora erythroseptica and Pythium ultimum and its relationship to mefenoxam-mediated control of pink rot and leak

In addition to cultural practices, the application of the fungicide mefenoxam is an important disease management tactic used to control both pink rot and leak on potato tubers grown in the USA. Mefenoxam resistance has been identified in many of the potato growing regions, and therefore resistance management strategies are very important for retaining this fungicide as a tool to manage these storage rot diseases. The relationship between mefenoxam efficacy and cultivar susceptibility to pink rot and leak was assessed in post‐harvest inoculation studies. Mefenoxam was applied to potato (Solanum tuberosum) cultivars known to express varying levels of susceptibility to pink rot and leak caused by Phytophthora erythroseptica and Pythium ultimum, respectfully. Tubers harvested from plants treated with in‐furrow and foliar applications of mefenoxam were inoculated with isolates sensitive to the fungicide. Incidence and severity of both diseases ranged widely among cultivars. Russet Norkotah was the most susceptible to infection by P. erythroseptica, while cvs Pike and Atlantic were the most resistant. Cultivars Dark Red Norland, Russet Norkotah, Goldrush and Russet Burbank were most susceptible to infection by P. ultimum whereas Snowden was most resistant. Control of pink rot differed significantly among cultivars following mefenoxam treatment, ranging from 28% (cv. Goldrush) to 67% (cv. Snowden) and generally provided the greatest level of disease control on susceptible and moderately susceptible cultivars such as Russet Norkotah and Snowden, respectively. In contrast, the impact of mefenoxam on leak development was minimal and disease control did not differ significantly among the cultivars. The fungicide failed to control leak in the susceptible cvs Atlantic and Pike and control ranged from 1.7% to 5.2% in cvs Goldrush, Russet Norkotah, Dark Red Norland, Russet Burbank and Kennebec. The greatest level of leak control was achieved with the moderately resistant cv., Snowden, at 12.7%. Cultivars most likely to benefit from mefenoxam treatments should be targeted as part of a pink rot management programme. Judicious use of the fungicide, when matched with the level of cultivar susceptibility, may prove to be an efficient and effective approach to reduce infection rates and possibly manage mefenoxam resistance thereby maintaining longevity of the compound.     

Breeding success of the colonist species Bubulcus ibis (Linnaeus, 1758) and four native species

This work evaluated the breeding success of Bubulcus ibis (Ardeidae), Egretta thula, Nycticorax nycticorax, Phimosus infuscatus and Plegadis chihi in Rio Grande do Sul during two consecutive nesting seasons. Mean clutch size for B. ibis was 2.59 in 1998/1999 and 2.49 in 1999/2000. The species with both the smallest and largest clutch was P. infuscatus, with 2.04 in 1999/2000, and 3.16 in 1998/1999. The highest mean number of nestlings per nest was 2.86 for P. chihi in 1998/1999 and the lowest was 1.85 for B. ibis in 1998/1999 and P. infuscatus in 1999/2000. In both nesting seasons all the species had major success, laying three eggs and raising two nestlings, exept for B. ibis. The breeding success for P. chihi varied from 1.54 young/nest in 1998/1999 to 0.4 in 1999/2000, whereas B. ibis ranged from 1.16 in the first period to 0.99 in the second.     

Effectiveness of some substances in the control of carrot and parsley roots against fungal diseases

Field experiments were carried out in the years 2005 and 2006 on carrot cv. 'Koral' and 'Perfekcja', and parsley cv. 'Berlinska' and 'Cukrowa'. Effectiveness of substances: Biochikol 020 PC (biologically active substances BAS--chitosan 20 g/dm3), Bioczos BR (extract of garlic 10 g/1 brick) and Biosept 33 SL (extract of grapefruit 33%) on seedling roots of carrot and parsley was studied. As the standard fungicide Zaprawa Funaben T (carbendazim 20% + tiuram 45%) was used. Roots of carrot and parsley were treated one of tested substances spring immediately before planting seedling roots. During vegetation period the growth of seedling shoots and setting of seeds, and their infestation by fungal and bacterial pathogens was noticed. Among substances used for spring dressing of carrot and also parsley seedling roots, the best efficacy exhibited Zaprawa Funaben T in both years of observation. The highest yield of carrot seeds had combination roots cv. 'Koral' and parsley seeds roots cvs 'Berlińska' and 'Cukrowa' dressed Zaprawa Funaben T. Effectiveness of biopreparates Biochikol and Biosept was lower in comparison with the standard fungicide, but their protective effect was significantly higher than in control. Bioczos had the lowest control efficacy.     

The influence of wind on spiral grain formation in conifer trees

The correlation between spiral grain formation and crown asymmetry was investigated in 18 Scots pine (Pinus sylvestris L.) and 17 Norway spruce [Picea abies (L.) Karst.] trees selected from clones of each species growing in the south of Sweden. The angle between the longitudinal direction of the tracheids in the outermost year ring compared to the longitudinal direction of the stem was measured by scribing lines which followed the direction of the tracheids. The crown asymmetry was measured by taking photographs of the trees followed by a simple picture analysis of the tree. Wind data for the growing seasons of 1997 and 1998 were obtained from the Swedish Meteorological and Hydrological Institute. The results showed a significant correlation between the angle of the tracheids compared to the stem longitudinal direction going from a left-handed angle if the trees had a crown projected to the north towards a right-handed angle the more the crown projects to the south. Received: 6 September 1999 / Accepted: 20 January 2000     

Interactions between perennial ryegrass ( Lolium perenne L.) and white clover (Trifolium repens L.) under contrasting nitrogen availability: productivity,seasonal patterns of species composition,N2 fixation,N transfer and N recovery

Nitrogen (N) fertiliser and clover cultivar choice affect competition and productivity in grass-clover mixtures. Pure stands and mixtures of perennial ryegrass and white clover cultivars with contrasting growth habits were examined. The aim of this work was to study the effect of repetitive nitrogen (N) application and cultivar combination on competition and productivity, N yield in the harvested herbage, N₂ fixation in mixtures and pure stands, and transfer of N from clover to the companion grass. Large-leaved white clover cultivar Alice and small-leaved cv. Gwenda and perennial ryegrass cvs. Barlet (erect) and Heraut (prostrate) were sown in pure stands and as four binary grass-clover mixtures on a sandy soil in 1995. In the mixtures, two levels of N fertiliser were applied: 0 (-N) and 150 and 180 kg ha^-1 y^-1 N (+N) in 1996 and 1997, respectively, while the grass monocultures received three N levels (0, 140/180 and 280/360 kg ha^-1) in 1996 and 1997, respectively. No N was applied to pure clover. The plots were cut five times during 1996 and six times during 1997. Fertiliser N was applied in early spring and after every harvest. The treatments were continued until the summer of 1999. In pure grass, the applied N was effectively recovered. In mixtures, N application affected competition by enhancing grass growth and the overall effect of N application was 17 kg DM per kg N applied in 1996. However, there was no yield response to N fertilizer in 1997, because this was compensated for by a higher clover production in unfertilised mixtures. In 1997, -N mixtures yielded more N than +N mixtures, owing to the higher clover content and N₂ fixation. Large-leaved clover cv. Alice was better able to withstand the negative effect of repetitive N application on clover production in mixtures and increased its proportion during the growing season of the second harvest year. In 1997, mixtures with Alice yielded more N than mixtures with Gwenda, but in pure clover swards, there was no cultivar effect on N yield. Also, during the autumn of 1998 and the spring of 1999, the clover content was highest in mixtures with Alice. Harvested N and apparent N₂ fixation were almost twice as high in 1997 as in 1996. N yield and apparent N₂ fixation were higher in pure clover than in mixtures. In mixtures, the apparent N₂ fixation in 1996 was 142 kg N ha^-1, irrespective of cultivar or N treatment. In 1997, it was on average 337 kg N ha^-1, and higher in -N mixtures and in mixtures with Alice. For each tonne of clover DM in the harvested herbage, 65 and 57 kg N was harvested in 1996 and 1997 in -N mixtures, respectively. The apparent transfer of clover-derived N to grass was on average 29 and 70 kg N ha^-1 yr^-1 in 1996 and 1997, respectively. It was highest in +N mixtures and highest in mixtures with Gwenda in 1997. In contrast to clover, the grass cultivars were very similar in their productivity and seasonal patterns, despite their contrasting growth habits. Seasonal trends in N yield, N transfer and N recovery are discussed in relation to fertilizer application regimes and variation in production patterns in mixtures and pure stands. This revised version was published online in June 2006 with corrections to the Cover Date.     

Systemic fungicides in the control of strawberry wilt (Verticillium dahliae)

In a series of experiments between 1970 and 1973 the application of benomyl or thiophanate methyl to field-grown strawberries, planted on Verticillium-mtested land, gave control of wilt for up to 5 months, the duration of control being related to the amount of fungicide applied in the spring. Treatment of inoculated plants grown on in chloropicrin-fumigated soil was effective for at least two seasons. An autumn-planted multi-factorial experiment in heavily-infested soil showed that, to achieve maximum wilt control, it was advantageous to grow cv. Gorella rather than cv. Cambridge Vigour; to drench the runners at planting rather than to dip them in the fungicide suspension; and to use a high concentration (0–075 % a-i-) and large volume (600 ml per plant) for a supplementary treatment in May rather than a lower concentration (0.025 %) ^or smaller volume (400 ml). There were small but significant advantages in applying benomyl rather than thiophanate methyl, and in using 0–2% a.i. suspension at planting rather than 0–05%. No advantage was gained by dividing the spring application into two equal doses applied 2 wk apart. Extrapolation from the logarithmic relation between wilt index and total dose of fungicide applied in the spring suggested that I.I g/plant would have given almost complete control until October; such control had been achieved in an earlier experiment in which 1–2 g/plant was applied. Crop yield in the second year was determined by the treatment applied in the first year, but although these treatments had given significantly better control of wilt in Gorella than in Cambridge Vigour, the greater growth and yield potentials of the latter cultivar had an over-riding effect on crop production; Cambridge Vigour yielded more than Gorella under all chemical treatments, but in the absence of treatment Gorella gave a larger crop than Cambridge Vigour. A proposed regime, entailing spring and autumn applications, is aimed at minimizing the colonization of the plant throughout the year, thus reducing the production of new inoculum and, by limiting the quantity of the pathogen in contact with the systemic chemicals, minimizing the probability of selecting fungicide-resistant variants of V. dahliae.     

Genetic diversity among cultivars of spring barley revealed by random amplified polymorphic DNA (RAPD)

RAPD (random amplified polymorphic DNA) polymorphism was studied in 23 malting and non-malting spring barley cultivars included in the official list of Polish cultivated varieties. Twenty-four 10-mer primers were tested in each cultivar, giving altogether 149 amplification products, 45% of which were polymorphic. The number of polymorphic bands revealed by one primer ranged from 1 to 6, with an average of 2.8. Genetic distance for all pairs of compared varieties was estimated and a dendrogram was constructed using unweighted pair group method of arithmetic means. The genetic distance between cultivars ranged from 0.11 for cvs. Apex and Bryl to 0.62 for cvs. Orthega and Madonna. Of the seven malting cultivars only two (Brenda and Stratus) formed one group at D = 0.25. The genetic distance between cvs. Brenda and Scarlett, especially recommended for brewery, was equal to 0.34. The detected polymorphism appeared to be sufficient for assessing genetic distances between cultivars, but on the basis of this polymorphism groups of malting and non-malting cultivars were not clearly distinguished.     

Chemical techniques for control of stem canker and black scurf (Rhizctonia solani) disease of potatoes

Thiabendazole, iprodione and benodanil were tested for control of stem canker and black scurf disease of potatoes using seed tubers with or without black scurf planted in soil infested or not with Rhizoctonia solani . Dormant seed tubers were treated with fungicide dusts, dips or sprays and before planting dusts were applied to soil or to sprouts on seed tubers.
Plants grown from seed tubers with black scurf had more stem canker, stolon infection and Thanatephorus cucumeris and progeny tubers had more black scurf than from seed without black scurf. Infesting soil with R. solani increased black scurf but not stem canker or stolon infection.
Fungicide treatment of seed tubers controlled all phases of the disease and sprout and soil treatments also had significant effects. Numbers of tubers in July were usually increased by treatment although by harvest many small tubers (>3 cm) had been resorbed. Fungicide treatment substantially increased yield only when shoot tips were pruned by R. solani .
Regression analyses showed that stolon pruning, Thanatephorus and black scurf were significantly related to stem canker, and numbers of tubers in July but not in September were inversely related to stolon pruning.
The significance of sources of inoculum and the effects of controlling disease on tuber production are discussed in relation to methods of fungicide use.     

Bee population returns and cherry yields in an orchard pollinated with Osmia lignaria (Hymenoptera: Megachilidae)

During 1998-2003, we used populations of the solitary bee Osmia lignaria Say to pollinate a commercial sweet cherry orchard in northern Utah. Bee densities released each year ranged from 1290 to 1857 females/ha, with approximately twice as many males. Female progeny produced each year were greater than parental populations released, except in 2003, when nesting was poor due to bird predation. Despite poor weather during bloom, and in contrast to most other local producers, the study orchard produced harvestable crops in 1999 (2,964 kg/ha) and 2001 (3,154 kg/ha). In 1998 and 2000, record yields were obtained (10,625 and 12,096 kg/ha, respectively). Including only those years with harvestable crops, average production was 2.2 times higher in 1998-2003 (when O. lignaria populations were used) compared with 1992-1997 (when 10 Apis mellifera hives were used). This is the first study reporting multiyear cherry yields in an orchard pollinated with O. lignaria in North America.     

Additional human remains from Blombos Cave, South Africa: (1999-2000 excavations)

The uppermost Middle Stone Age (MSA) layers at Blombos Cave contain high densities of Still Bay bifacial points. Information from other regional sites places the Still Bay prior to the Howiesons Poort industry, which has been dated at 65-70 ka. The Blombos Cave MSA strata have yielded nine human teeth or dental fragments. Four that were recovered during the 1997-1998 excavations have been published elsewhere. The remaining five were discovered during the 1999-2000 field seasons; these are described here. Three of the new specimens are deciduous teeth, and two are permanent premolar and molar crown fragments. The entire dental sample probably represents at least five and as many as seven individuals. The deciduous teeth from the upper MSA levels are likely to have been exfoliated in the cave. One deciduous tooth and the permanent tooth fragments from the lower MSA levels probably represent three individuals who died in or near the cave. The Blombos Cave premolars preserve horizontal circum-cervical striae suggestive of palliative tooth pick use. Approximately half of the permanent and deciduous crown diameters exceed those of recent Africans; for the remainder, the fossil values fall among modern African sample means. The Blombos Cave tooth crowns tend to be smaller than the majority of penecontemporaneous Neandertal teeth. The morphology of the Blombos Cave di is comparable to MSA homologues from the nearby, and presumably somewhat younger site of Die Kelders Cave 1.     

Habitat of the corn leafhopper (Hemiptera: Cicadellidae) during the dry (winter) season in Mexico

Although the corn leafhopper Dalbulus maidis (DeLong and Wolcott) is the most important vector of maize pathogens in Latin America, little is known about how and where it overwinters (passes the dry season), particularly in Mexico. The objectives of this study were (1) to monitor the abundance of D. maidis adults throughout the dry season in maize and maize-free habitats and (2) to determine where and how D. maidis adults, exposed or nonexposed to the maize pathogen Spiroplasma kunkelii Whitcomb, overwinter in a maize-free habitat. Work for the first objective was done during the two consecutive dry seasons of 1999-2000 and 2000-2001; the second objective was done during the dry seasons of 2003-2004 and 2005-2006. During the dry winter seasons, D. maidis was prevalent as long as maize was present in irrigated areas. The leafhopper was found in 52 of the 58 irrigated maize fields sampled in Mexico at the end of the dry seasons of 1999-2000 and 2000-2001. However, leafhopper adults were not found in nonirrigated maize-free habitats at high elevation during the dry winter season (February, March, and April), although leafhopper adults were prevalent on perennial wild grasses in January after maize harvest. Additional experiments revealed, however, that corn leafhopper adults, although few in number, survived the entire dry season in these nonirrigated maize-free fields. Also, no detectable difference in survival existed between leafhoppers exposed and those not exposed to S. kunkelli during the two dry seasons in the maize-free habitat.     

Effects of previous cropping and fungicide timing on the development of light leaf spot (Pyrenopeziza brassicae), seed yield and quality of winter oilseed rape (Brassica napus)

Light leaf spot, caused by Pyrenopeziza brassicae, was assessed regularly on double-low cultivars of winter oilseed rape during field experiments at Rothamsted in 1990-91 and 1991-92. Previous cropping and fungicide applications differed; seed yield and seed quality were measured at harvest. In each season, both the initial incidence of light leaf spot and the rate of disease increase were greater in oilseed rape crops sown after rape than those sown after cereals. The incidence of diseases caused by Phoma lingam or Alternaria spp. was also greater in second oilseed rape crops. In 1991-92 there was 42% less rainfall between September and March than in 1990-91, and much less light leaf spot developed. However, P. lingam and Alternaria spp. were more common. Only fungicide application schedules including an autumn spray decreased the incidence of light leaf spot on leaves, stems and pods, as indicated by decreased areas under the disease progress curves (AUDPC) and slower rates of disease increase. Summer sprays decreased incidence and severity of light leaf spot on pods only. In 1990-91, all fungicide treatments which included an autumn spray increased seed and oil yields of cv. Capricorn but only the treatment which included autumn, spring and summer sprays increased yields of cv. Falcon. No treatment increased the yields of cv. Capricorn or cv. Falcon in 1991-92. Fungicide applications decreased glucosinolate concentrations in the seed from a crop of cv. Cobra severely infected by P. brassicae in 1990-91, but did not increase yield.