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Very close up shot of wheat crop ears in field

Disease survey highlights

CROPMONITOR - WINTER WHEAT COMMERCIAL CROPS SURVEY 2012

HEADLINES:

  • Each crop received an average of 3.7 fungicide applications, the highest ever recorded since the survey began in 1975.
  • Four crops were untreated, 3 of these were organic crops.
  • There was a marked increase in SDHI fungicides for the second year running, with 64.3% crops treated in 2012, compared to 23.2% in 2010 and 50.3% in 2011.

  • The proportion of crops receiving sprays at T1 (91%) decreased from last year (96%). At T0 (67%), T2 (88%) and T3 (79%) the proportion of crops receiving sprays increased compared with 2011 (61%, 76% and 69% respectively).
  • This season, total foliar disease recorded on the top two leaves was the highest since 1985.
  • With 97% crops affected, the incidence of Septoria tritici was the highest ever recorded since the survey began and it remains the most common foliar disease.
  • Powdery mildew affected 4% of crops, this is the lowest proportion of crops affected by powdery mildew since the survey began and markedly lower than last year when 34% crops were affected.
  • Tan spot was the third most common foliar disease in the survey, affecting 14% of crops. This is the lowest incidence of tan spot since 2008.
  • Yellow rust was recorded in 3% of samples, slightly lower than last year when it affected 6% of surveyed samples.
  • Brown rust was recorded in 17% of samples, the highest incidence recorded since 2007 (when 50% of samples were affected). This year, brown rust was the second most common foliar disease.
  • Septoria nodorum was not recorded in the survey for the second year running.
  • Cephalosporium leaf stripe was not recorded in the survey for the second year running.
  • The incidence of Didymella exitialis was markedly higher than in previous years, affecting 7.4% crops in the survey – the highest incidence since 1988 when 15.8% crops were affected. This year D. exitialis was the fourth most common foliar disease.
  • The incidence and severity of eyespot was at the highest level since 2008. 
  • Fusarium stem base symptoms were the highest ever recorded since the survey began. There was a marked increase in ear blight incidence, with the highest incidence ever recorded since the survey began.
  • Incidence of glume spot decreased from the levels recorded in 2011.  

National and regional severity of diseases

Septoria tritici levels were the highest of all the foliar diseases, with 5% mean area of the flag leaf and 9.6% mean area of leaf 2 affected. This is the highest severity of S. tritici since 1985 (when 5% and 15% mean area of the flag leaf and leaf 2 respectively were affected). Mildew levels (with less than 0.01% area of both the flag leaf and leaf 2 affected) were markedly reduced from previous years and the long-term mean (1998-2007), and is the lowest severity of powdery mildew since the survey began. The severity of tan spot (0.04% mean area of leaf 2 affected) was slightly lower than last year (when 0.07% mean area of leaf 2 was affected) but higher than the long-term mean. (Figure 1).

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

Nationally, 97%of surveyed samples were affected by S. tritici, this is the highest proportion of samples affected since the survey began and markedly higher than levels seen in previous years and the long-term mean (1998-2007). S. tritici remains the most common foliar disease – a position it has held since 1990. Mildew incidence (3.7% samples affected) was markedly lower than in any other year since the survey began and also markedly lower than the long-term mean. The previous lowest incidence was in 2007, when 11% of samples were affected. Since 2007, mildew has been the second most common foliar disease but this year it became the fifth most common disease. Tan spot was the third most commonly occurring disease for the fourth year in succession, however, with 14% samples affected this year, the incidence was the lowest seen since 2008 (Figure 2).

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

The incidence and severity of S. tritici were both highest in the North West region, with 100% crops and 14.3% of leaf 2 affected. The incidence was lowest in the South West, where 87.5% samples were affected, and severity was lowest in the North East where 4.2% mean area of leaf 2 was affected. (Figure 3).

Figure 3 - Regional incidence and severity of S. tritici

Tan spot was recorded in all regions in the survey, with the exception of the North West. The incidence of tan spot was highest in the East Midlands where 24% crops were affected. Severity was low in all regions but was highest in the East where 0.1% leaf 2 area was affected. In all other regions less than 0.05% leaf 2 was affected. (Figure 4).

Figure 4 - Regional incidence of tan spot

Brown rust was the second most common foliar disease in the survey and affected 17% of samples. This is the highest incidence of brown rust since 2007 (when 50% samples were affected). Brown rust was recorded in all regions in the survey, with the exception of the North West and incidence and severity were both highest in the East where 35% samples and 0.1% leaf area were affected. The incidence of yellow rust was slightly lower than last year, with 3% samples affected compared with 6% in 2011. The region with the highest incidence was the South West, with 6% samples affected, followed by the South East, with 5% samples affected (Figure 5).

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

Mean levels of damaging eyespot (as moderate + severe symptoms) were the highest recorded since 2008. (Figure 6).

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

Regionally, Yorkshire had the highest levels of damaging eyespot and the East had the lowest.There were no severe symptoms recorded in the South West region (Figure 7).

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

The incidence of Fusarium stem base diseases, with 34% stems affected, was the highest recorded in the survey since 1993 (when 48% stems were affected). Nodal fusarium affected 25% of stems which is the highest level since 1993 when 28% stems were affected. Mean levels of severe symptoms of nodal Fusarium were the highest ever recorded since the survey began. Internodal fusarium affected 14% stems in the survey, the highest level since 2008 when 22% stems were affected. Severe symptoms of internodal fusarium affected 1.1% stems which is by far the highest ever recorded since the survey began - the previous highest ever figure was only 0.25% stems affected (in 2011) (Figure 8).

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

Ear blight symptoms were recorded at the highest ever levels since the survey began, with 96% of samples and 54% ears affected, previous to this, the highest ever incidence was in 2007 when 82% crops and 20% ears were affected.Glume spot on the other hand was recordedat lower levels thanlast year,with 45% crops and 4% ears affected compared with 57% crops and 6% ears in 2011. (Figure 9)

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

Cultivar use

Thirty five different cultivars of winter wheat were encountered during the 2012 survey(Fig. 10). Oakley was the most popular cultivar for the fourth year running and accounted for 11.5% of the sample. Of the ten most popular cultivars (see Figure 10), the highest average level of S. tritici was recorded on Alchemy with 14.4% of leaf 2 affected. The lowest was on Invicta, with 2.2% of leaf 2 affected.

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

The incidence of tan spot was highest in JB Diego with 34.4% samples affected (Figure 11). This was followed by Invicta with 27.3% samples affected. In 2011, JB Diego was also the most commonly affected of the ten most popular cultivars, with 33.3% samples affected and in 2010, was the second most commonly affected cultivar, with 22.2% samples affected.

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 Invicta had the lowest total foliar disease severity with 2.7% area of leaf 2 affected (Fig. 12) and the cultivar with the highest was Alchemy, with 14.6% area of leaf 2 affected. Alchemy was also the cultivar with the highest disease severity in 2011, with 2.1% area of leaf 2 affected. S. tritici and tan spot were the only foliar diseases present on leaf 2 in all ten most popular cultivars. In a comparison of the 10 most popular cultivars, mildew was most severe on Oakley, S. tritici on Alchemy, tan spot on Solstice, yellow rust on KWS Santiago and brown rust severity was highest on Invicta. Levels of moderate + severe eyespot were highest on Invicta (with an average of 16.0% stems affected) and were the lowest on Alchemy (with an average of 2.1% stems affected). The highest severity of Fusarium stem base symptoms was the highest on Duxford, with an average of 21.4% of stems affected with moderate or severe symptoms, which was predominantly by moderate nodal infections. Cordiale was the next highest, with and average of 15.4% stems affected – again predominantly by moderate nodal infections. Invicta was the least affected, with an average of 7.3% stems affected.

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.

Sowing dates

In 2012, 18.4% of crops were drilled before the 20th September (Fig. 13), this is slightly lower than last year, when 19.1% of crops were sown during this period. This is the second highest proportion sown at this time since 2007. 39.9% of crops were sown between the 20th and 30th September, this is highest proportion of crops sown at this time since the survey began. 21.6% of crops were drilled between the 1st and 10th of October, this is slightly lower than last year, when 19.5% crops were sown at this time. Between the 11th and 20th October, 11.5% crops were sown, the lowest proportion of crops sown during this period since 2006, when 11.2% were sown. The proportion of crops (2.9%) sown later than the 20th October was the lowest ever recorded in the survey.

Figure 13 - Sowing dates of survey crops (%)

This year, the eyespot index was generally higher than last year at all sowing dates (Fig 14.). Historically, there has been a trend for eyespot to be less severe on crops sown after 10thOctober, however, this year the eyespot index was highest for those crops.

Figure 14 – Eyespot index with sowing dates

Fungicide use

  • The use of chlorothalonil, from the phthalonitrile group, was slightly higher than last year (with 72% crops treated compared with 69%) and was the second most used fungicide group in the survey this year. Although the proportion of crops treated with chlorothalonil was slightly higher than last year (when the proportion of crops treated with chlorothalonil dropped markedly) it was still lower than those seen in years previous to 2011. This year, chlorothalonil treated crops received an average of 1.6 applications/crop, this was lower than last year when they received an average of 1.7 applications/crop and continues the downward trend seen in recent years. Chlorothalonil use in all treated crops averaged 1.13 applications each, the lowest amount since 2004, when crops received an average of 1.12 applications each.

  • At key stage T0, chlorothalonil use increased to 39% this year from 37% in 2011. The proportion of crops receiving T1 and T2 applications containing chlorothalonil decreased from last year, with 50% and 15% of crops receiving application containing chlorothalonil compared with 52% and 19% respectively in 2011. There was a slight increase at T3 when 9% crops were treated this year compared with 7% last year.

  • 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, which was the same as last year. DMI treated crops received an average of 3.3 DMI sprays each, compared with 3.0 in 2011, 3.1 in 2010 and 2.9 in 2009.

  • DMI applications at each key stage this year were broadly similar to those in 2011. Nineteen per cent of DMI applications were applied at T0 (18% in 2011), 28% at T1 (32% in 2011), 27% at T2 (26% in 2011), 24% at T3 (23% in 2011) and 2% at T4 (1% in 2011). Sixty per cent of crops received 3 or more applications containing at least one DMI product per application.

  • The use of fungicides from the strobilurin group decreased markedly from last year, with 71% crops receiving a strobilurin treatment compared with 81% in 2011. The majority of strobilurin treatments were single sprays applied only once per crop (61%). Six per cent of applications were aimed at T0 this year, compared to 4% aimed at T0 last year. Forty-one per cent of applications were aimed at T1, an increase from the 40% aimed at T1 last year. At T2, 31% crops received a strobilurin treatment, less than the 41% aimed at T2 last year and at T3, 20% of crops received a strobilurin treatment compared with 24% last year.

  • This year crops treated with a strobilurin received an average of 1.4 applications/crop, slightly lower than last year’s average of 1.5 applications/crop. Strobilurin use across all treated crops averaged 1.0 applications/crop. This was lower than the average of 1.2 applications/crop last year.

  • The proportion of crops receiving morpholine fungicides remained consistent of 2011. This year, 38% of treated crops received at least one application compared with 38% in 2011. Like last year, the most common spray timing was T1; 35% of crops treated at this time received applications of fungicides from this group (39% in 2011), followed by T0 with 26% of crops treated (16% in 2011). On average, crops received 1.4 applications/crop of morpholine fungicides, which was the same as last year.

  • There was a marked increase in the use of SDHI fungicides (succinate-dehydrogenase inhibitors) for the second year running. Sixty-four per cent of crops received at least one application of SHDI fungicides, this compares with 28%, 23%, 23% and 50% from 2008 – 2011 respectively. The most common spray timing for this fungicide group was T2 when 41% crops were treated at this time, followed by T1 when 38% crops were treated. SDHI treated crops received an average of 1.3 applications/crop, an increase from the average of 1.2 appications/crop in 2011.

  • Overall, surveyed crops received an average of 3.7 fungicide applications, higher than last year’s average of 3.2 fungicide applications. This is the highest average number of fungicide treatments applied to surveyed crops since the survey began and continues the upward trend in fungicide usage.

Figure 15 – Fungicide applications during the growing season.

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).