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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.


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).