The effects of post‐harvest curing and storage temperature on severity of black dot, caused by Colletotrichum coccodes, were investigated for potato crops grown for different crop durations (days from 50% emergence to harvest) in soils that posed a low, medium and high risk of disease. In field trials over four growing seasons (2005–8), black dot severity at harvest increased with increasing crop duration, within the range 103–146 days from 50% emergence to harvest (P < 0.05). In field trials over three growing seasons (2006–8), black dot severity on tubers at harvest increased significantly with increasing soil inoculum in each year, within the range 43–4787 pg C. coccodes DNA/g soil (P < 0.05). Storage trials were conducted to measure the influence of accumulated post‐harvest temperature on black dot. In 2005, no difference in black dot severity was observed on tubers stored for 20 weeks at 2.5 and 3.5 °C. In 2006 (but not 2007), increasing the duration of curing after harvest from 4 to 14 days increased black dot severity on tubers from 8.9 to 11.2% (P < 0.01) in long duration crops (>131 days after 50% emergence) grown under high (>1000 pg C. coccodes DNA/g soil) soil inoculum. The number of days of curing did not affect disease severity for shorter duration crops grown at high soil inoculum, or on crops grown at medium or low (100–1000 and <100 pg C. coccodes DNA/g soil, respectively) soil inoculum concentrations. Soil inoculum and crop duration together provided a reasonable prediction of black dot severity at harvest and after a 20‐week storage period.

Field trials were carried out over a 4 year period (2004–2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in‐furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004, 2005 and 2006, two field trials were performed each year and in 2007, 19 mini‐field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide‐untreated plots, 43·8% of tubers of cv. Maris Piper were unmarketable, compared with 17·0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.

Steven J Moloney, Yongji Huang, Avice Hall, M. Ashworth, Peter Gladders, Bruce D.L. Fitt, ‘How interactions between phoma stem canker pathogens are influenced by fungicides’, paper presented at the Crop Protection in Southern Britain, Peterborough, UK, 27-28 November, 2012.

Global food security is threatened by crop diseases that account for average yield losses of 16%. Climate change is exacerbating threats to food security in much of the world, emphasising the need to increase food production in northern European countries such as the UK. However, to mitigate climate change, crops must be grown so as to minimise greenhouse gas emissions (GHG); results with UK oilseed rape demonstrate how disease control in arable crops can contribute to climate change mitigation. However, work examining impacts of climate change on UK epidemics of winter oilseed rape diseases illustrates unexpected, contrasting impacts of climate change on complex plant-disease interactions. In England, phoma stem canker is expected to become more severe whilst light leaf spot is expected to become less severe. Such work can provide guidance for government and industry planning for adaptation to impacts of climate change on crops to ensure future food security.

To illustrate impacts of climate change on plant disease epidemics, an oilseed rape crop growth model, and weather-based disease forecasting models for phoma stem canker (Leptosphaeria maculans) and light leaf spot (Pyrenopeziza brassicae) were combined with projected UK temperature and rainfall under high and low carbon emissions climate change scenarios for the 2020s and 2050s. It was predicted that, if diseases are controlled, oilseed rape yields will increase, especially in Scotland. However, it was also predicted that phoma stem canker epidemics will not only increase in severity but also spread northwards from England to Scotland by the 2020s and that yield losses will increase to 50% in southern England if diseases are not controlled. There is evidence that the major gene for resistance to L. maculans Rlm6 is temperature-sensitive, since it operated at 15°C but not at 25°C. These results provide a stimulus to develop models to predict effects of climate change on other crop diseases. Such predictions can be used to guide policy and practice in adapting to effects of climate change on food security.

Global food security is threatened by crop diseases that account for average yield losses of 16%. Climate change is exacerbating the threats to food security in many areas of the world, emphasising the need to improve crop yields to increase food production in northern European countries such as the UK. However, to mitigate climate change, the crops must be grown in such a way as to minimise greenhouse gas emissions (GHG) and optimise inputs associated with their production. As examples, it is estimated that UK production of winter oilseed rape and winter barley is associated, respectively, with GHG of 3300 and 2617 kg CO2 eq. ha-1 of crop, with >70% of the GHG associated with the use of nitrogen fertiliser. Furthermore, it is estimated that control of diseases by use of fungicides in UK oilseed rape and barley is associated, respectively, with decreases in GHG of 100 and 50 kg CO2 eq. t-1 of seed. These results demonstrate how disease control in arable crops can make a contribution to both climate change mitigation and sustainable arable crop production. Climate change will affect both growth of agricultural crops and diseases that attack them but there has been little work to study its combined effects on crop-disease interactions to guide strategies for adaptation to climate change. For example, it may take 10-15 years to develop a new fungicide and it is important to identify future target diseases now. As examples, the impact of climate change on UK epidemics of phoma stem canker and light leaf spot on winter oilseed rape and fusarium ear blight on winter wheat is investigated by combining weather-based disease models, crop growth models and simulated weather for different climate change scenarios. It is predicted that climate change will increase the risk of oilseed rape phoma stem canker and wheat fusarium ear blight epidemics but decrease the risk of light leaf spot epidemics by the 2050s. Such predictions illustrate unexpected, contrasting impacts of climate change on complex plant-disease interactions in agricultural and natural ecosystems. They can provide guidance for government and industry planning for adaptation to effects of climate change on crops to ensure future food security.

Controlled‐environment and field experiments were done to quantify the individual contribution of seed‐tuber and soilborne inoculum of Colletotrichum coccodes in causing black dot disease of potato tubers. Seed‐tuber and soilborne inocula of C. coccodes were quantified using an existing real‐time PCR assay and related to subsequent incidence and severity of disease. In four field trials, a controlled‐environment experiment and through the monitoring of 122 commercial crops, seed‐tuber inoculum was found to be relatively less important than soilborne inoculum in causing black dot, and the level of seed‐tuber inoculum did not significantly affect either the incidence or severity of disease or the percentage of progeny tubers deemed unmarketable. By contrast, soilborne inoculum had the potential to result in high levels of disease and the level of C. coccodes soil infestation (pg DNA g−1 soil) was found to have a significant effect. At soil infestation levels below 100 pg DNA C. coccodes g−1 soil, 7% of commercial crops had an incidence of black dot greater than 20%, increasing to 40% and 57% of crops at levels of 100–1000 pg g−1 and >1000 pg g−1 soil, respectively. These arbitrary threshold levels for soilborne inoculum related to disease risk are discussed. Interpretation of disease risk based on inoculum levels must, in the future, be informed by agronomic variables and potential control strategies.

Global food security is threatened by crop diseases that account for average yield losses of 16 per cent, with the greatest losses experienced by subsistence farmers in the developing world. Climate change is exacerbating the threats to food security in such areas, emphasizing the need to increase food production in northern European countries such as the UK. However, the crops must be grown in such a way as to minimize greenhouse gas (GHG) emissions associated with their production. As an example, it is estimated that production of UK winter oilseed rape is associated with GHG of 3300 kg CO2 eq. ha−1 of crop and 834 kg CO2 eq. t−1 of seed yield, with 79 per cent of the GHG associated with the use of nitrogen fertilizer. Furthermore, it is estimated that control of diseases by use of fungicides in this UK oilseed rape is associated with a decrease in GHG of 100 kg CO2 eq. t−1 of seed. Winter oilseed rape cultivar disease resistance is associated with a decrease in GHG of 56 kg CO2 eq. t−1, although this figure is an underestimate. These results demonstrate how disease control in arable crops can make a contribution to both climate change mitigation and sustainable arable crop production to ensure global food security.

In June/July 2001, 2002, 2003 and 2006, regional variation in distribution of the pathogens Leptosphaeria maculans and L. biglobosa that are causally associated with phoma stem canker was surveyed on winter oilseed rape crops in England. In 2001–2003, when isolates from basal cankers were visually identified as L. maculans or L. biglobosa based on cultural morphological characteristics, 70% were L. maculans and 30%L. biglobosa. In 2001, 2002, 2003 and 2006, when amounts of DNA of each species in basal cankers were determined by quantitative PCR, the abundance of L. maculans DNA was greater than that of L. biglobosa DNA in 77% of samples. When regional differences in amounts of L. maculans and L. biglobosa DNA were mapped geostatistically, quantities of L. maculans DNA were greater in cankers from southern England and those of L. biglobosa DNA were greater in northern England. A comparison with geostatistically mapped predictions made using a weather‐based model describing stages in development of phoma stem canker epidemics suggested that these differences in Leptosphaeria populations may have been a consequence of differences in temperature after onset of leaf spotting between northern and southern England. Both PCR and morphological evidence suggested that the abundance of L. maculans in England has increased since the last surveys in the 1980s. Implications of these surveys for control of phoma stem canker are discussed.

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 pound in 1998, 1.6M pound in 1999 and 0.37M pound in 2000 (when the area of winter linseed had decreased greatly). Estimated combined losses on winter and spring linseed were approximately 14.8M pound in 1998, 34.9M pound in 1999 and 11.0M pound in 2000.