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Disease survey highlights

Brown rust risk map
Disease survey highlights
Defra Winter Wheat Commercial Crops Disease Survey 2018


Introduction

Two hundred and fifty winter wheat crops were surveyed for symptoms of disease in July 2018, 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 and the incidence of ear diseases were all lower than last year.
  • Z. tritici remains the most common foliar disease although incidence and severity were both much lower than last year.
  • Tan spot incidence was the lowest since 2004, with 2% crops affected. The disease was only the fifth most common of the main foliar diseases, having been third most common in 2017. Highest levels of tan spot were in 2011 when 23% of crops were affected.
  • Powdery mildew affected 21% of crops and was the second most common of the main foliar diseases. Although lower than last year (24% crops affected), it is the second highest incidence since 2011, indicating a slight resurgence in this disease in recent years.
  • Brown rust affected 8.7% of crops this year, lower than last year, but higher than in all other previous years since 2012.
  • Yellow rust affected 1.7% crops this year, the lowest incidence since 2015 when it was not recorded in the survey.
  • Septoria nodorum was not recorded in the survey this summer. This is the 8th 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 eighth year running.
  • Overall, stem base fusarium (both nodal and internodal) was lower than last year. Nodal fusarium levels were the lowest recorded since 2010.
  • On the ears, 22% crops were affected with ear blight which was markedly lower than last year and the lowest since 2011. Fusarium glume spot was also much lower than last year, with 17% crops showing symptoms.
  • In 2018, the sowing date profile was similar to 2017, with more later sown crops.
  • Crops received an average of 3.4 fungicide applications, lower than in 2017 (3.7) and the lowest since 2013.
  • The proportion of crops drilled after minimum tillage was the highest ever recorded (60% crops).
  • There was only one crop (organic) this year that did not receive a fungicide treatment.
  • There was a slight increase in the use of SDHI (succinate dehydrogenase inhibitor) fungicides. 97% of crops received at least one SDHI fungicide compared to 96% in 2017.
  • The proportion of crops receiving sprays was lower at all key spray timings, principally at T0.

National and regional incidence and severity of diseases


(a) Zymoseptoria tritici, mildew and tan spot

Zymoseptoria tritici levels were lower than those seen last year (Figure 1). On the flag leaf this year, a mean of 0.4% leaf area was affected compared with 1.4% leaf area affected last year. On leaf 2, a mean of 1.8% leaf area was affected compared with 2.6% mean leaf area affected in 2017. Levels of Z. tritici on both the flag and second leaf this year were much lower the long-term mean (2004-2013) of 1.2% and 3.2% mean leaf area affected respectively. The severity of tan spot, with less than 0.001% mean leaf area affected on both the flag leaf and leaf 2, was lower than both the previous year (when less than 0.02% and 0.06% mean area of flag leaf and leaf 2 were affected respectively), and the long-term mean (0.02% and 0.03% mean area of the flag leaf and leaf 2 affected respectively). This year saw the lowest severity of tan spot since 2004, when there was also less than 0.001% mean area of the flag leaf and leaf 2 affected respectively. Mildew severity was similar to both last year and the long-term mean, with the flag leaf having 0.02% mean leaf area affected compared with 0.02% in 2017 and the long-term mean of 0.03%. Leaf 2 had 0.09% mean leaf area affected compared with 0.06% last year and a mean of 0.08% over the last ten years. This year was the highest severity of mildew seen on leaf 2 since 2011, when there was also 0.09% mean leaf area affected.

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

Nationally, 71% of surveyed crops were affected by Z. tritici (Figure 2). This was lower than both last year (81% crops affected) and the long-term mean (2004-2013) of 79% crops affected. Z. tritici remains the most common foliar disease – a position it has held since 1990. Tan spot affected 2% crops this summer, markedly lower than both last year (12% crops affected) and the long-term mean (12% crops affected) and was the lowest incidence of tan spot since 2004 (when 1% crops were affected). Mildew incidence, with 21% crops affected, was slightly lower than both last year (24% crops affected) and the long-term mean (26% crops affected).

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

Regionally, the highest incidence of Z. tritici was in the West Midlands, where 87% crops were affected and the lowest was in the North West, where it was not recorded on any surveyed crops on the top two leaves (6 crops surveyed in this region) (Figure 3). Within crops, the severity of Z. tritici was highest in the West Midlands (4.2% leaf 2 affected), and lowest in the North West and North East.

Figure 3 - Regional incidence and severity of Z. tritici.

This year, tan spot was only recorded in four regions in the survey – Yorkshire, East Midlands, West Midlands and the South East (Figure 4). The incidence of tan spot was highest in the South East where 6% crops were affected, followed by the West Midlands (4% crops affected), Yorkshire (3% crops affected) and the East Midlands (2% crops affected). Severity was low in all regions where tan spot was recorded but was highest in the South East where 0.007% mean area of leaf 2 was affected.

Figure 4 - Regional incidence of tan spot.

(b) Brown rust and yellow rust

Despite the hot dry conditions in summer 2018, the incidence of brown rust was lower than last year, with 9% crops affected compared with 11% in 2017 (Figure 5). Within crops, 0.02% (flag) and 0.04% (leaf 2) mean leaf areas were recorded and this was also slightly lower than both last year (0.08% and 0.05% mean leaf area affected respectively) and the long-term mean (2004-2013) (0.07% and 0.1% mean leaf area affected respectively). Brown rust was not recorded on crops in the North East, North West and East Midlands regions of the survey (data not shown); this is the second consecutive year it has not been recorded on surveyed crops in the North East and North West. The South East was the region with the highest incidence with 23% crops affected.

Yellow rust affected 1.7% crops this year and within crops, less than 0.01% mean leaf area was affected on both the flag leaf and leaf 2. The incidence was slightly lower than both last year when yellow rust affected 2% crops and the long-term mean of 2.2% crops affected. 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 only recorded in crops in four regions of the survey, the North East, Yorkshire, West Midlands and the East. The North East had the highest incidence of yellow rust, with 10% crops affected (data not shown).

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

(c) Eyespot

Mean levels of damaging eyespot (as moderate + severe symptoms) were lower than last year, with 3.8% stems affected nationally compared with 6.0% in 2017 (Figure 6).

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

Regionally, the West Midlands had the highest levels of damaging eyespot (6.1% stems affected) and the North East had the lowest with 1.6% stems affected (Figure 7). Slight and moderate symptoms were recorded in all regions in the survey whilst severe symptoms were recorded in all regions except the North East, North West and the West Midlands.

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

(d) Fusarium stem base and ear disease

Incidence of stem base fusarium in 2018 (26% stems affected) was lower than last year (when 38% stems were affected) and was the lowest since 2007 when 21% stems were affected (Figure 8). Nodal fusarium affected 22% of stems, which was lower than last year when 32% stems were affected. Slight symptoms of nodal fusarium (17% stems affected) were the lowest recorded in the survey since 2011, when 14.9% stems were affected, however, moderate and severe symptoms (4.5% and 0% stems affected respectively) were both at the lowest levels seen since 2008, when 2.4% and 0% stems were affected respectively. Internodal fusarium affected 10% of stems which was lower than last year when 16% stems were affected. Slight, moderate and severe levels of internodal fusarium were all lower than those seen last year, with 8.4%, 1.7 % and 0.02% compared with 12.9%, 3.4% and 0.1% stems affected respectively. The levels of severe internodal fusarium were the lowest seen since 2004, when 0.01% stems were affected.

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

Incidence of ear blight symptoms was substantially lower than last year, with 22% crops and 2% ears affected compared with 76% of crops and 16% ears affected in 2017 (Figure 9). This was the lowest incidence of ear blight since 2011 when 21.0% crops were affected. Glume spot was also recorded at significantly lower levels than last year (with 17% crops and 1% ears affected compared with 47% crops and 5% ears affected in 2017) and was the lowest incidence of glume spot since 2015, when 14% crops and 1% ears were affected. Regionally, the South East had the highest incidence of ear blight, with 48% crops affected and the North East and North West had the lowest, with no crops affected in these regions (data not shown). The South East also had the highest incidence of glume spot, with 42% samples affected and again, the lowest was the North East and the North West where there were no crops affected.

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


(a) Cultivar use

Forty-one different cultivars of winter wheat were encountered during the 2018 survey maintaining a diverse number of varieties being grown and no one variety dominating the national cropping area. Skyfall was the most popular variety this year (for the second year running) and it accounted for 11.8% of the sample (Figure 10). Of the ten most popular cultivars, the highest average level of Z. tritici was recorded on KWS Barrel (rating 4.4 for resistance to Z. tritici) with 4.0% of leaf 2 affected. The lowest was on Shabras (rating 6.2), with 0.1% of leaf 2 affected and this was followed by Graham (rating 6.7), with 0.4% of leaf 2 affected. Shabras and Barrel were the least popular of the 10 most widely grown varieties in 2018.

Figure 10. Severity of Zymoseptoria tritici on the main cultivars (mean percentage area of leaf 2 affected) and popularity of cultivars (percentage of survey sample).

In the ten most popular cultivars of 2018, the incidence of tan spot was highest in KWS Barrel, with 14.3% samples affected (Figure 11). This was followed by Graham, (8.7% samples affected) KWS Kerrin, (7.7% samples) and Skyfall (3.7% samples). Tan spot was only recorded in these four out of the ten most popular cultivars in 2018.

Figure 11. Incidence of tan spot on the main cultivars (% crops affected) and popularity of cultivars (percentage of survey sample).

A comparison of disease severity on the ten most popular cultivars showed that KWS Siskin had the lowest total foliar disease severity with 0.4% area of leaf 2 affected (Figure 12) and the highest was KWS Barrel, with 4.0% area of leaf 2 affected. KWS Siskin also had the lowest total foliar disease severity last year (2017) with 0.47% of leaf 2 affected. In a comparison of the 10 most popular cultivars, mildew was most severe on Crusoe, Z. tritici was most severe on KWS Barrel, Didymella leaf spot and tan spot were most severe on Skyfall and brown rust was most severe on Costello. 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 KWS Siskin, with an average of 8.7% stems affected, and the lowest on KWS Barrel, with an average of 0.6% stems affected. The highest severity of Fusarium stem base symptoms was on KWS Barrel, with an average of 10.9% stems affected with moderate or severe symptoms, this was closely followed by KWS Kerrin, with an average of 10.2% stems affected. KWS Lili was the least affected, with an average of 2.2% stems affected by moderate and severe infections.

Figure 12. Total foliar disease levels (average percentage of 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 2018 were similar to those seen in 2017, however, in previous years the vast majority of crops have been sown between 20th September and the 10th October but, as in 2017, the survey recorded a shift towards later sown crops, with the vast majority been sown between 1st and 20th October (Figure 13). Only three per cent of crops were drilled before the 20th September (compared with 8% in 2017) and this was the lowest proportion of crops drilled at this time since 1989 (1.4%). Nineteen percent of crops were sown between the 20th and 30th September, this was lower than last year when 24% crops were drilled at this time and the lowest proportion of crops drilled at this time since 2000 (15%). Between the 1st and the 10th October 32% of crops were drilled, this was very similar to last year (33% crops). Between the 11th and 20th October, 27% of crops were sown, this was much higher than the proportion of crops sown at this time in recent years and is the highest proportion since 2000, when there were also 27% crops drilled between these dates. The proportion of crops sown between the 21st and the 31st October was 13%, this was slightly lower than last year when 15% crops were drilled during this period and the proportion of crops drilled after 31st October was 6%, which is the highest proportion of crops sown at this time since 2014 (13%).

Figure 13. Percentage of survey crops sown by date.

This year, the eyespot index was lower than last year at all sow timings, except for the timing between 11th and 20th October when it was higher (Figure 14). Historically, there has been a trend for eyespot to be less severe on crops sown after 10th October and this can be seen again in 2018.

Figure 14. Levels of damaging eyespot (as moderate + severe symptoms) (% stems affected) in relation to sowing date.


(c) Tillage practice

Use of minimum tillage (including minimum tillage and direct drilling) has continued to increase in use since the upward trend started in 1998. After a period of equivalence with the frequency of use of ploughing in the period 2012-2016, minimum tillage has been the most commonly used tillage method over the last two years and in 2018 accounted for the highest proportion of crops ever recorded (Figure 15).

Figure 15. Percentage changes in tillage practice from 1998-2018.


(d) Fungicide use

Overall, surveyed crops received an average of 3.4 fungicide applications per crop, this was a lower number compared with last year (3.7 applications per crop) and is the lowest average number of fungicide treatments since 2013 (3.1 applications per crop). When compared with last year, the number of crops receiving a spray was lower at each T timing with the most noticeable difference being at the T0 timing (Figure 16), however, the overall pattern of most applications at T1, followed by T2, T3 and then T0 remains the same as it has historically. There is emerging evidence that fungicide use may be becoming more responsive to weather conditions, overall disease risks and economic factors with the T0 timing showing the most variability in use.

Figure 16. Fungicide applications made to crops at the key spray timings (T0 (target leaf 4), T1 (target leaf 3), T2 (target flag leaf) and T3 (target ear)).

Use of fungicide groups and active ingredients (ai)
The proportion of crops treated with different fungicide groups or chlorothalonil between 2014 and 2018 in shown in Figure 17. Ninety-five percent of crops surveyed received at least one treatment of one of the three main fungicide groups (DMI / SDHI / chlorothalonil)

(a) Chlorothalonil
The use of chlorothalonil, from the phthalonitrile group, was slightly higher than last year (with 94.9% crops treated compared with 93.3% in 2017) and was the third most used fungicide group in the survey this year (Figure 17). Although the proportion of crops treated with chlorothalonil dropped markedly in 2011, its use has been increasing again steadily, even though there was a slight drop in usage in 2017 compared with 2016. Chlorothalonil use in treated crops averaged 2.1 applications per crop, which was also the same as last year.

(b) DMIs
DMI (demethylation inhibitor) fungicides, comprising the imidazole and triazole chemical groups, were the most often used fungicide group, with 99% of treated crops receiving at least one application, this was a slightly lower proportion than last year when 100% crops received a treatment containing DMI and is the lowest proportion of crops receiving a treatment containing DMI since 2007 (98.9% crops). Where DMI fungicide were used within the spray programme, crops received an average of 3.0 applications/crop which was slightly lower than the 3.3 applications/crop last year (Figure 17).

(c) Strobilurins
Following the peak in use of fungicides from the strobilurin group in 2003, with 95% crops receiving a fungicide application containing strobilurin, use showed a steady decline until 2015. Since then strobilurin use has been rising very gradually again over the last three years. Although there was a slight decrease in use in 2017 (56% crops receiving at least one application), this has risen again to 58% crops in 2018. Crops treated with a strobilurin this year received an average of 1.4 applications per crop, which was the same as last year (Figure 17).
(d) SDHIs
There was a slight increase this year in the use of SDHI fungicides (succinate-dehydrogenase inhibitors) which, despite a slight dip in use last year, continues the trend of steadily rising over the past seven years. In 2016, they became the second most used fungicide group and this has continued ever since. Ninety-seven per cent of crops received at least one application of SDHI fungicides in 2018, this compares with 28%, 23%, 23%, 50%, 64%, 85%, 92%, 94%, 98% and 96% from 2008 – 2017 respectively. On average, crops received 1.9 applications/crop of SDHI fungicides, which was slightly higher than in 2017 when there were an average of 1.8 applications/crop (Figure 17).

(e) Morpholines
After showing a slow increase in use between 2014 and 2017, the proportion of crops receiving morpholine fungicides was slightly lower than that in 2017 (Figure 17). This year, 25% of treated crops received at least one application compared with 30% in 2017, 25% in 2016, 24% in 2015 and 24% in 2014. On average, crops received 1.2 applications per crop of morpholine fungicides, which was slightly higher than last year when it was 1.0 application per crop.

Figure 17. Fungicide use: percentage of treated crops receiving applications from the major fungicide groups and the active ingredient chlorothalonil post emergence. *Includes the chemical groups morpholines, piperidines and spiroketalamines (as reductase/isomerase inhibitors).

Use of fungicide groups and active ingredients at key spray timings
Use of different fungicide groups or chlorothalonil at the key spray timings is shown in Figure 18.

(a) Chlorothalonil
At key stage T0, chlorothalonil use decreased significantly this year, with 55% of crops receiving an application, compared with 74% in 2017 (Figure 18). The proportion of crops receiving T1 applications containing chlorothalonil increased from 74% of crops in 2017 to 79% of crops in 2018. There was also an increase in use at both the T2 and T3 timings this year, with 60% and 19% respectively compared with 52% and 15% respectively in 2017. No crops received an application containing chlorothalonil at T4 for the second year running.

(b) DMIs
DMI applications at each key stage this year were lower than those seen in 2017 (Figure 18). At T0, the proportion of crops receiving an application containing a DMI fungicide dropped from 63% in 2017 to 47% this year. At T1, 88% of fungicide treated crops received an application containing a DMI fungicide, compared with 90% crops in 2017. The proportion of crops receiving T2 and T3 applications containing DMI also decreased slightly from 91% and 80% of crops respectively in 2017, to 86% and 79% respectively in 2018. At T4 the proportion of crops receiving an application of DMI also decreased from 3% of fungicide treated crops in 2017 to 2% this year. Seventy-nine per cent of crops received 3 or more applications per crop containing at least one DMI product per application, which was lower than last year when it was 88% crops. There were no DMI-treated crops which received 5 or more applications containing at least one DMI product per application, last year this figure was 2% and in 2016 it was 8% crops.

(c) Strobilurins
Use of strobilurin applications at all timings were similar to last year. This year, 11% crops received a fungicide application containing at least one strobilurin at T0, 21% at T1, 23% at T2, 26% at T3 and 1% at T4. This compares with 8% at T0, 24% at T1, 27% at T2, 21% at T3 and 0% at T4 in 2017. Where strobilurins were applied to crops, this was most often as a single treatment (61%) and 36% crops received two applications per crop.

(d) SDHIs
This year, there was an increase in SDHI use at T0, T1 and T3 and a decrease at T2 compared with last year. The most common spray timing for this fungicide group was T2 when 83% crops were treated at this time (86% in 2017), followed by T1 when 81% crops were treated (73% in 2017). At T0, T3 and T4, there were 6%, 11% and 0% crops treated with a fungicide containing an SDHI respectively compared with 3%, 9% and 0% respectively in 2017. Eighty-four per cent of crops received 2 applications containing at least one SDHI product per application, an increase from last year when 77% crops received 2 applications containing an SDHI.

(e) Morpholines
The most common spray timing was T2; 11% of crops treated at this time received applications of fungicides from this group (which was higher than the 8% last year), this was followed by T1 with 10% (12% in 2017). There was a slight increase in use at the T3 timing this year with 6% of crops treated with a product containing morpholine compared with 5% in 2017.

Figure 18. Fungicide use: percentage of all crops treated at the key timings with the major fungicide groups and the active ingredient chlorothalonil post emergence in 2018. *Includes the chemical groups morpholines, piperidines and spiroketalamines (as reductase/isomerase inhibitors).