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Disease survey highlights

Brown rust risk map
Monitoring Regional Disease Risk
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.

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).
Figure 2 - National foliar disease incidence, main three diseases (mean % samples affected).
Figure 3 - Regional incidence and severity of Z. tritici.
Figure 4 - Regional incidence of tan spot.
Figure 5 - National foliar disease incidence, rusts (mean % samples affected).
Figure 6 - National levels of eyespot (mean % stems affected).
Figure 7 - Regional levels of eyespot (mean % stems affected).
Figure 8 - Incidence of stem base Fusarium (mean % stems 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).
Figure 11. Incidence of tan spot on the main cultivars (% crops affected) and popularity of cultivars (percentage of survey sample).
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.
Figure 13. Percentage of survey crops sown by date.
Figure 14. Levels of damaging eyespot (as moderate + severe symptoms) (% stems affected) in relation to sowing date.
Figure 15. Percentage changes in tillage practice from 1998-2018.
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)).
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).
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).