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Disease survey highlights

Brown rust risk map
Disease survey highlights
Defra Winter Wheat Commercial Crops Disease Survey 2019


Introduction

Two hundred and fifty winter wheat crops were surveyed for symptoms of disease in July 2019, 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 higher than last year.

Z. tritici remains the most common foliar disease and the incidence and severity were both higher than last year.

• Tan spot incidence was slightly higher than last year, with 6% crops affected. The disease was the joint fourth most common of the main foliar diseases. The highest levels of tan spot were in 2011 when 23% of crops were affected.

• Powdery mildew affected 12% of crops (lower than last year) and was the third most common of the main foliar diseases.

• Brown rust affected 4.5% of crops this year which was lower than last year. Brown rust was the fifth most common foliar disease in the survey this summer.

• Yellow rust affected 5.7% crops this year, the highest incidence since 2016. Yellow rust was the joint fourth most common disease 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 ninth year running.

• Overall, stem base fusarium (both nodal and internodal) was higher than last year. The incidence of internodal fusarium was the highest recorded since 2008.

• On the ears, both glume blotch and ear blight were recorded at higher levels than in the previous year.

National and regional incidence and severity of diseases

(a) Zymoseptoria tritici, mildew and tan spot

Zymoseptoria tritici levels were higher than those seen last year (Figure 1). On the flag leaf, a mean of 1.0% leaf area was affected compared with 0.4% leaf area affected last year. On leaf 2, a mean of 2.1% leaf area was affected compared with 1.8% mean leaf area affected in 2018. Levels of Z. tritici on both the flag and second leaf were however lower the long-term mean (2005-2014) of 1.7% and 4.0% mean leaf area affected respectively. The severity of tan spot, although very low, with 0.002% and 0.007% mean leaf area affected on the flag leaf and leaf 2 respectively, was slightly higher than the previous year (less than 0.001% mean leaf area of both the flag leaf and leaf 2 affected), but lower than the long-term mean (0.02% and 0.03% mean area of the flag leaf and leaf 2 affected respectively). This year saw the second lowest severity (after last year) 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 lower than both last year and the long-term mean, with the flag leaf having 0.001% mean leaf area affected compared with 0.02% in 2018 and the long-term mean of 0.02%. Leaf 2 had 0.01% mean leaf area affected compared with 0.09% last year and a mean of 0.07% over the last ten years. This year was the lowest severity of mildew seen since 2012, when there was 0.0004% and 0.003% mean leaf area affected on the flag leaf and leaf 2 respectively.

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

Nationally, 80% of surveyed crops were affected by Z. tritici (Figure 2). This was higher than both last year (71% crops affected) and the long-term mean (2005-2014) of 79% crops affected. Z. tritici remains the most common foliar disease – a position it has held since 1990. Tan spot affected 6% crops this summer, higher than last year (2% crops affected) but lower than the long-term mean (13% crops affected). Mildew incidence, with 12% crops affected, was lower than both last year (21% crops affected) and the long-term mean (23% crops affected).

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

Regionally, the highest incidence of Z. tritici was in the North West, where 100% crops were affected and the lowest was in the North East, where 73% crops were affected (Figure 3). Within crops, the severity of Z. tritici was also highest in the North West (6.6% leaf 2 affected), and lowest in the South West (1.3% leaf 2 affected).

Figure 3 - Regional incidence and severity of Z. tritici

This year, tan spot was not recorded in two regions in the survey – the North East and North West (Figure 4). The incidence of tan spot was highest in the West Midlands where 8% crops were affected. Severity was low in all regions where tan spot was recorded but was highest in the East Midlands, where 0.01% mean area of leaf 2 was affected.

Figure 4 - Regional incidence of tan spot


(b) Brown rust and yellow rust


This summer, the incidence of brown rust was lower than last year, with 4% crops affected compared with 9% in 2018 (Figure 5). Within crops, 0.04% (flag) and 0.04% (leaf 2) mean leaf areas were recorded and this was very similar to last year (0.02% and 0.04% mean leaf area affected respectively) but lower than the long-term mean (2005-2014) of 0.07% and 0.1% mean leaf area affected respectively. Brown rust was not recorded on crops in the North East, North West and West Midlands regions of the survey (data not shown); this is the third 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 12% crops affected.

Yellow rust affected 6% 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 higher than both last year (1.7% crops affected) and 2017 (2% crops affected), and also higher than the long-term mean of 2.4% crops affected. Within crops, the severity was also higher than the long-term mean on the flag leaf but slightly lower on leaf 2. Yellow rust was not recorded on crops in the North West and West Midlands regions of the survey. The East had the highest incidence of yellow rust, with 11% crops affected (data not shown).

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


(c) Eyespot


Although mean levels of slight eyespot were lower than last year (8.8% compared with (9.5%), mean levels of damaging eyespot (as moderate + severe symptoms) were slightly higher than last year, with 3.9% stems affected nationally compared with 3.8% in 2018 (Figure 6).

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

Slight and moderate symptoms were recorded in all regions in the survey whilst severe symptoms were recorded in all regions except the North West, South East and the South West (Figure 7). Regionally, the West Midlands had the highest levels of damaging eyespot (8.2% stems affected) and the South East had the lowest with 0.4% stems affected.

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


(d) Fusarium stem base and ear disease

Incidence of stem base fusarium in 2019, with 35% stems affected, was higher than both last year (26% stems were affected) and the long-term mean (2005-2014) of 29% stems affected (Figure 8). Nodal fusarium affected 26% of stems, which was higher than both last year (22% stems affected) and the long-term mean (20% stems affected). Symptoms of slight, moderate and severe nodal fusarium were all higher than in the previous year with 21.7%, 4.5% and 0.03% stems affected respectively compared with 17.2%, 4.5% and 0% stems affected respectively in 2018. Internodal fusarium affected 20% of stems which was much higher than last year when 10% stems were affected and this was the highest incidence since 2008, when 22% stems were affected. Slight, moderate and severe levels of internodal fusarium were all higher than those seen last year, with 15.2%, 4.5% and 0.2% compared with 8.4%, 1.7% and 0.01% stems affected respectively in 2018. The levels of slight internodal fusarium were the highest seen since 2013, moderate symptoms the highest since 2008 and severe symptoms the highest since 2014.

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

Incidence of ear blight symptoms was markedly higher than last year, with 70% crops and 10% ears affected compared with 22% of crops and 2% ears affected in 2018 (Figure 9). Glume spot was also recorded at much higher levels than last year (with 51% crops and 5% ears affected compared with 17% crops and 1% ears affected in 2018) and was the highest incidence of glume spot since 2011, when 57% crops and 6% ears were affected. Regionally, the East Midlands had the highest incidence of ear blight, with 96% crops affected and the South East had the lowest, with 45% crops affected (data not shown). The South East also had the lowest incidence of glume spot, with 33% crops affected and the highest was the North West, with 83% crops affected.

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