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Disease survey highlights

Defra Winter Wheat Commercial Crops Disease Survey 2017


Introduction


Two hundred and fifty winter wheat crops were surveyed for symptoms of disease in July 2017, with the number of crops monitored in each region being proportional to the area of wheat grown.

Summary highlights

  • This season, total foliar disease recorded on the top two leaves was higher than the last two years, primarily due to higher levels of Zymoseptoria tritici.
  • Z. tritici remains the most common foliar disease. Incidence and severity were both the highest since 2014.
  • Tan spot incidence was higher than last year, with 12% crops affected. Tan spot was the third most common of the main foliar diseases.
  • Powdery mildew affected 24% of crops and was the second most common of the main foliar diseases. Mildew levels have declined in recent years but this was the highest incidence since 2011.
  • Brown rust affected 11% of crops this year, the highest incidence since 2012. Disease severity was also increased with levels being the highest since 2007.
  • Yellow rust affected 2% crops this year, which was equivalent to the long-term average for this disease.
  • Septoria nodorum was not recorded in the survey this summer. This is the 7th time this disease has not been found in the survey in the last ten years.
  • Cephalosporium leaf stripe was not recorded in the survey for the seventh year running.
  • Overall, the incidence of stem base fusarium (both nodal and internodal) was lower than last year. However, moderate symptoms of nodal fusarium were the highest seen since 1992.
  • On the ears, 76% crops were affected with ear blight, lower than last year when 84% crops were affected. Fusarium glume spot was recorded at the highest level seen since 2011, with 47% crops showing symptoms.
  • In 2017, the sowing date profile was slightly different to that seen in 2016, with more later sown crops. However, as in the last few years, the majority of crops were sown between 20th September and the 10th October.
  • Surveyed crops received an average of 3.7 fungicide applications, the same number of applications as last year.
  • All surveyed crops received at least one fungicide treatment this year.
  • There was a slight decrease in the use of SDHI fungicides this year. In 2017, 96% of crops received at least one treatment containing an SDHI fungicide.
  • The proportion of crops receiving sprays was lower at all key spray timings with the exception of T0, which was much higher than last year – 83% crops compared with 35% in 2016. This was the highest proportion of crops treated at the T0 timing since the survey began.

National and regional incidence and severity of diseases


(a) Zymoseptoria tritici, mildew and tan spot

Z. tritici levels were higher than those seen in the last two years (Figure 1). On the flag leaf this year, a mean of 1.4% leaf area was affected compared with 0.1% leaf area affected last year and this was the highest severity of Z. tritici on the flag leaf since 2014 (when 5.9% mean leaf area was affected). On leaf 2, a mean of 2.6% leaf area was affected this year compared with 0.7% mean leaf area affected last year. Levels of Z. tritici on the flag leaf this year (1.4% mean leaf area affected) was very similar to the long-term mean (2003-2012) of 1.3% mean leaf area affected but lower on leaf 2 (2.6% this year compared with 3.6% long-term mean leaf are affected). The severity of tan spot (0.02% mean area of flag leaf affected and 0.06% mean area of leaf 2 affected) was slightly higher than in the previous year (when less than 0.01% and 0.02% mean area of flag leaf and leaf 2 were affected respectively), and was also slightly higher than the long-term mean (0.01% and 0.03% mean area of the flag leaf and leaf 2 affected respectively). Mildew levels were also slightly higher this year. The incidence of 0.02% on the flag leaf and 0.06% on leaf 2 were the highest seen since 2013 when 0.03% (flag) and 0.08% (leaf 2) mean leaf areas were recorded. However, the incidence of mildew this year was lower than the long-term mean of 0.03% on the flag leaf and 0.09% mean leaf area affected on leaf 2.

Figure 1 - National foliar disease levels (mean % area leaf 2 affected)

Nationally, 81% of surveyed crops were affected by Z. tritici (Figure 2). This was higher than both last year (72% crops affected) and 2015 (61% crops affected), but lower than the long-term mean (2003-2012) of 82% crops affected. Z. tritici remains the most common foliar disease – a position it has held since 1990. Tan spot affected 12% crops this summer, this was higher than last year when 7% crops were affected and higher than the long-term mean of 11% crops affected. Mildew incidence, with 24% crops affected, was much higher than last year (7% crops affected) but lower than the long-term mean (27% crops affected).

Figure 2 - National foliar disease incidence, main three diseases (mean % samples affected)

Regionally, the highest incidence of Z. tritici was in Yorkshire, where 94% crops were affected and the lowest was in the North East, where 50% crops were affected (Figure 3). The severity of Z. tritici was highest in the South West, where 9.8% leaf 2 was affected, and lowest in the North East, where 0.3% of leaf 2 was affected.

Figure 3 - Regional incidence and severity of Z. tritici

Tan spot was recorded in all regions in the survey except the North East and the North West (Figure 4). The incidence of tan spot was highest in the West Midlands where 21.7% crops were affected, followed by the South East, where 21.2 crops were affected. Severity was low in all regions but was highest in the South East where 0.2% leaf 2 area was affected.

Figure 4 - Regional incidence of tan spot

(b) Brown rust and yellow rust

In the survey this summer, the incidence of brown rust was much higher than last year, with 11% crops affected compared with 2% in 2016 (Figure 5) and was the highest incidence of brown rust in the survey since 2012, when 17% crops were affected. Within crops, 0.09% (flag) and 0.05% (leaf 2) mean leaf areas were recorded and this was the highest severity of brown rust since 2007 when 0.27% and 1.14% mean leaf areas were recorded respectively. However, the incidence this summer was the same as the long-term (2003-2012) mean of 11% crops affected. Brown rust was recorded on crops in all regions of the survey, with the exception of the North East and North West. The South East was the region with the highest incidence with 21% crops affected.

Yellow rust affected 2% crops this year and within crops less than 0.01% mean leaf area was affected on both the flag leaf and leaf 2. This was lower than last year when yellow rust affected 7% crops. The incidence this summer was also slightly lower than the long-term mean of 2.2% crops affected and within crops the severity was also lower than the long-term mean of 0.01% mean leaf area affected on both the flag leaf and leaf 2. Yellow rust was recorded in crops in most regions of the survey, it was not recorded on crops in the North East, East Midlands and South East. The North West had the highest incidence of yellow rust, with 17% crops affected.

Figure 5 - National foliar disease incidence, rusts (mean % samples affected)

(c) Eyespot

Mean levels of damaging eyespot (as moderate + severe symptoms) were very slightly higher than last year, with 6% stems affected nationally, compared with 5.6% last year (figure 6).

Figure 6 - National levels of eyespot (mean % stems affected)

Regionally, the West Midlands had the highest levels of damaging eyespot (15% stems affected) and the East had the lowest with 3% stems affected (Figure 7). Moderate symptoms were recorded in all regions in the survey and severe symptoms were recorded in all regions except the North East, North West and the South West.

Figure 7 - Regional levels of eyespot (mean % stems affected)

(d) Fusarium stem base and ear disease

The incidence of fusarium stem base in 2017 (38% stems affected) was lower than last year (when 47% stems were affected), this has been the first drop in incidence since 2014 after which it had been showing an increasing trend (Figure 8). Nodal fusarium affected 32% of stems, which was lower than last year when 43% stems were affected. Moderate symptoms of nodal fusarium (8.5% stems affected) were the highest recorded in the survey since 1992, when 12.5% stems were affected, however, slight and severe symptoms were both lower than last year with 23.4% and 0.02% stems affected with slight and severe symptoms respectively, compared with 35.7% and 0.05% stems affected respectively in 2016. Internodal fusarium affected 16% of stems which was higher than last year when 12% stems were affected. Slight, moderate and severe levels of internodal fusarium were all higher than those seen last year, with 12.9%, 3.4% and 0.08% compared with 10.6%, 1.6% and 0.03% stems affected respectively.

Figure 8 - Incidence of stem base Fusarium (mean % stems affected)

Incidence of ear blight symptoms was lower than last year, with 76% samples and 16% ears affected compared with 84% of samples and 21% ears affected in 2016 (Figure 9). Although lower than last year, it is the second highest incidence of ear blight since 2012, when 96% samples were affected. Glume spot was recorded at much higher levels than last year (with 47% samples and 5% ears affected compared with 39% samples and 3% ears affected in 2016) and this is the highest incidence of glume spot since 2011, when 57% samples and 6% ears were affected. Regionally, the West Midlands had the highest incidence of ear blight, with 91% crops affected and the North East had the lowest (with 60% crops affected). The North West had the highest incidence of glume spot, with 67% samples affected and the lowest was the North East (with 20% crops affected).

Figure 9 - Incidence of ear Fusarium (mean % samples affected)

AGRONOMIC PRACTICE


(a) Cultivar use
Thirty-four different cultivars of winter wheat were encountered during the 2017 survey (Figure 10). Skyfall was the most popular variety this year and it accounted for 12.9% of the sample. In 2016 Skyfall was the second most popular and accounted for 13.9% of the sample. Of the ten most popular cultivars (see Figure 10), the highest average level of Z. tritici was recorded on JB Diego (resistance rating 5) with 5.96% of leaf 2 affected. The lowest was on KWS Siskin (resistance rating 7), with 0.4% of leaf 2 affected and this was followed by Skyfall (resistance rating 6), with 0.9% of leaf 2 affected.

Figure 10 – Severity of Z. tritici on the main cultivars (mean per cent area leaf 2 affected) and popularity of cultivars.

In the ten most popular cultivars of 2017, the incidence of tan spot was highest in Dickens, with 33% samples affected (Figure 11). This was followed by Leeds which had 25% samples affected. Tan spot was recorded in nine of the ten most popular cultivars in 2017, but was not recorded on Evolution for the second year running.

Figure 11 – Incidence of tan spot on the main cultivars (per cent samples affected) and popularity of cultivars.

A comparison of disease severity on the ten most popular cultivars showed that KWS Siskin had the lowest total foliar disease severity with 0.47% area of leaf 2 affected (Figure 12) and the highest was JB Diego, with 6.17% area of leaf 2 affected. In the previous two years (2016 and 2015) Skyfall was the cultivar with the lowest total foliar disease severity – this year it was the second lowest, with 1.07% area of leaf 2 affected. In a comparison of the 10 most popular cultivars, mildew, brown rust and tan spot were most severe on Leeds, Z. tritici and yellow rust were most severe on JB Diego and Didymella leaf spot was most severe on Skyfall. Z. tritici was the only foliar disease present on leaf 2 in all ten most popular cultivars. Levels of moderate + severe eyespot were highest on JB Diego, with an average of 8.5% stems affected, and the lowest on Revelation, with an average of 0.7% stems affected. The highest severity of Fusarium stem base symptoms was on KWS Lili, with an average of 18.2% stems affected with moderate or severe symptoms. Leeds was the next highest, with an average of 17% stems affected. Dickens was the least affected, with an average of 8% stems affected by moderate and severe infections.

Figure 12 – Total foliar disease levels (average per cent leaf 2 affected), eyespot severity (moderate + severe categories) and stem base Fusarium (moderate + severe categories) for the most popular cultivars.

(b) Sowing dates

The profile of sowing dates for crops surveyed in 2017 were similar to those seen in 2016, with the vast majority of crops sown between the 20th September and the 10th October. Eight per cent of crops were drilled before the 20th September – this was the same proportion as 2016. Twenty-four percent of crops were sown between the 20th and 30th September, this was lower than last year when 36% crops were drilled at this time. Between the 1st and the 10th October 33% of crops were drilled, this was higher than last year (28% crops). Nineteen per cent crops were drilled between the 11th and 20th October, which was similar to 2016 when 17% crops were sown between these dates. The proportion of crops sown between the 21st and the 31st October was 15%, this was higher than last year when 7% crops were drilled during this period. The proportion of crops drilled after 31st October was 2%, this is the lowest proportion of crops sown at this time since the survey began.

Figure 13 - Sowing dates of survey crops (%)

The eyespot index was higher than last year at the three earlier sowing timings, and lower than last year at the three later sowing timings (Figure 14). Historically, there has been a trend for eyespot to be less severe on crops sown after 10th October.

Figure 14 – Eyespot index with sowing dates

(c) Fungicide use

Overall, surveyed crops received an average of 3.7 fungicide applications per crop, which was the same amount as last year and is the second highest average number of fungicide treatments since the survey began in 1970 (2014 was the highest with an average of 3.8 applications per crop). At the T0 timing, the number of crops receiving a spray was much higher in 2017 than it was in 2016 (Figure 15), being the highest proportion of crops receiving a T0 spray since the survey began. However, the number of crops receiving subsequent sprays at T1, T2 and T3 was lower in 2017 than in 2016.

Figure 15 – Fungicide applications during the growing season.

  • The use of chlorothalonil, from the phthalonitrile group, was slightly lower than last year (with 93% crops treated compared with 95% in 2016) and was the third most used fungicide group in the survey this year (Figure 16). Although the proportion of crops treated with chlorothalonil dropped markedly in 2011, its use has been increasing again steadily, even with a slight drop in usage this year. In 2017, chlorothalonil treated crops received an average of 2.3 applications/crop, this was the higher than last year when crops received an average of 1.9 applications/crop. Chlorothalonil use in all treated crops averaged 2.2 applications per crop, also higher than last year when it was 1.8 applications/crop. At key stage T0, chlorothalonil use increased significantly this year, with 74% of crops receiving an application containing chlorothalonil, compared with 30% in 2016, 70% in 2015 and 41% in 2014. The proportion of crops receiving T1 applications containing chlorothalonil decreased from last year, with 74% of crops receiving an application containing chlorothalonil, compared with 83% in 2016 but there was a slight increase in use at both the T2 and T3 timings, with 52% and 15% respectively compared with 49% and 13% respectively in 2016. No crops received an application containing chlorothalonil at T4, compared to 2% crops in 2016.
  • DMI (demethylation inhibitor) fungicides, comprising the imidazole and triazole chemical groups, were the most often used fungicide group, with 100% of treated crops receiving at least one application, this was the same proportion as the previous two years and a slight increase from 2014 when this figure was 99.7% crops. DMI treated crops received an average of 3.3 applications/crop which was slightly higher than the 3.0 applications/crop last year.
  • DMI applications at each key stage this year were generally lower than those seen in 2016, with the exception of T0 where there was a increase in use. At T0, the proportion of crops receiving an application containing a DMI fungicide rose from 28% in 2016 to 63% this year. At T1, 90% of fungicide treated crops received an application containing a DMI fungicide, which was the lower than 2016 when it was 92% crops. The proportion of crops receiving T2 and T3 applications containing DMI also decreased slightly from 94% and 84% of crops respectively in 2016, to 91% and 80% respectively in 2017. At T4 the proportion of crops receiving an application of DMI last year also decreased from 9% of fungicide treated crops receiving an application in 2016 to 3% this year. Eighty-eight per cent of crops received 3 or more applications per crop containing at least one DMI product per application, which was slightly higher than last year when it was 85% crops. There were 2% of DMI treated crops which received 5 or more applications containing at least one DMI product per application - this figure was 8% crops in 2016.
  • Since the use of fungicides from the strobilurin group peaked in 2003, with 95% crops receiving a fungicide application containing strobilurin, their use has been in steady decline ever since. Although there was a slight increase in use last year: 57% crops receiving at least one application, this has dropped slightly to 56% crops this year. Crops treated with a strobilurin this year received an average of 1.4 applications per crop, which was the same as last year.
  • Use of strobilurin applications was similar to last year at all timings. This year, 8% crops received a fungicide application containing at least one strobilurin at T0, 24% at T1, 27% at T2, 21% at T3 and 0% at T4. This compares with 4% at T0, 23% at T1, 28% at T2, 23% at T3 and 0% at T4 in 2016. Where strobilurins were applied to crops, this was most often as a single treatment (61%). Thirty-five percent of crops received two strobilurin applications per crops and 2% per cent received three applications/crop.
  • There was a slight decrease this year in the use of SDHI fungicides (succinate-dehydrogenase inhibitors) after steadily rising for the past five years. Last year they became the second most used fungicide group and this year was the same. Ninety-six per cent of crops received at least one application of SDHI fungicides in 2017, this compares with 28%, 23%, 23%, 50%, 64%, 85%, 92%, 94% and 98% from 2008 – 2016 respectively. SDHI treated crops received an average of 1.8 applications/crop, this was the same proportion of applications per crop as both 2016 and 2015.
  • This year, there was an increase in SDHI use at T0 and T1 and a decrease at T2, T3 and T4 compared with last year. The most common spray timing for this fungicide group was T2 when 86% crops were treated at this time (90% in 2016), followed by T1 when 73% crops were treated (72% in 2016). At T0, T3 and T4, there were 3%, 9% and 0% crops treated with a fungicide containing an SDHI respectively. Seventy-seven per cent of crops received 2 applications containing at least one SDHI product per application, a slight decrease from last year when 78% crops received 2 applications containing an SDHI.
  • The proportion of crops receiving morpholine fungicides was again higher than those seen in previous years. This year, 30% of treated crops received at least one application compared with 25% in 2016, 24% in 2015, 24% in 2014 and 25% in 2013. Like last year, the most common spray timing was T1; 12% of crops treated at this time received applications of fungicides from this group (which was the same proportion as last year), this was followed by T2 with 8% (8% in 2016). At T3 and T4 timings, the proportion of crops treated with an application containing a morpholine was the same as last year, 5% and 2% respectively. On average, crops received 1.0 applications per crop of morpholine fungicides, which is slightly lower than last year when it was 1.3 applications per crop.

Figure 16 - Fungicide use: per cent of treated crops receiving applications from the major fungicide groups and the ai. chlorothalonil post-emergence. * Includes the chemical groups morpholines, piperidines and spiroketalamines (as reductase/isomerase inhibitors).

Figure 17 - Fungicide use: per cent of all crops treated at the key timings with the major fungicide groups and the ai. chlorothalonil post-emergence. * Includes the chemical groups morpholines, piperidines and spiroketalamines (as reductase/isomerase inhibitors).