Phoma leaf spot forecast

As one of the most important diseases of winter oilseed rape in England, it is important to keep on top of the phoma threat. Varietal resistance is the foundation of control. However, a well-timed fungicide spray(s) is sometimes necessary too.
How to manage phoma leaf spot and stem canker in oilseed rape

About the phoma leaf spot forecast

The timing of fungicide applications is important to achieve phoma control. Use fungicides in response to disease forecasts, crop monitoring and thresholds.

Temperature and rainfall information (1 July to 26 September) is used to simulate the development of Leptosphaeria maculans, a key pathogen responsible for phoma leaf spot and phoma stem canker.

Accounting for subsequent crop infection, the forecast (published in October) predicts the date when 10% of oilseed rape plants could potentially show symptoms of phoma leaf spot*. This level of infection relates to a treatment threshold for varieties with lower disease ratings for stem canker (7 and below).

*Note: Localised rain events are highly influential. Dates for 10% leaf spotting can vary tremendously (by a month or more), even at sites close to those monitored in the forecast. The forecast provides a general indication of the risk trends for the season and can only support field-level data and monitoring.

Phoma forecast (autumn 2020)

Map pin colour Phoma infection forecast status

No symptoms
Infection started
10% incidence
No data

Raw data (2020)

Location 2020 forecast 2019 forecast Difference 2020-2019 Latitude Longitude
KINLOSS 10/11/2020 08/10/2020 33 57.6494 -3.5606
DYCE 19/10/2020 22/10/2020 -2 57.2036 -2.1886
LEUCHARS 15/10/2020 14/10/2020 2 56.377 -2.862
CARLISLE 16/09/2020 11/09/2020 5 54.89549 -2.93531
FYLINGDALES 29/09/2020 19/10/2020 -20 54.362 -0.673
LEEMING 12/10/2020 20/10/2020 -8 54.296 -1.53
LECONFIELD 02/10/2020 13/10/2020 -11 53.87718 -0.44691
WADDINGTON 19/10/2020 10/10/2020 9 53.16625 -0.52427
CONINGSBY 02/10/2020 09/10/2020 -6 53.094 -0.171
CRANWELL 07/10/2020 05/10/2020 2 53.031 -0.502
WEYBOURNE 26/09/2020 23/10/2020 -27 52.94454 1.133602
SHAWBURY 04/10/2020 13/10/2020 -8 52.794 -2.663
MARHAM 28/09/2020 14/10/2020 -15 52.651 0.569
WITTERING 14/10/2020 01/10/2020 14 52.6111 -0.459
COLESHILL 13/10/2020 05/10/2020 9 52.48 -1.689
TRAWSGOED 27/09/2020 09/10/2020 -12 52.33518 -3.95938
ABERPORTH 28/09/2020 29/10/2020 -31 52.139 -4.571
WATTISHAM 08/10/2020 14/10/2020 -6 52.123 0.961
BEDFORD 28/09/2020 15/10/2020 -16 52.10673 -0.42279
PERSHORE 07/10/2020 06/10/2020 1 52.09363 -2.13995
ANDREWSFIELD 10/10/2020 14/10/2020 -4 51.896 0.453
ROTHAMSTED 13/09/2020 06/10/2020 -23 51.80814 -0.36136
BENSON 13/10/2020 15/10/2020 -2 51.62 -1.097
LYNEHAM 11/10/2020 08/10/2020 4 51.5031 -1.9924
HEATHROW 08/10/2020 10/10/2020 -1 51.479 -0.449
MANSTON 18/10/2020 21/10/2020 -2 51.3422 1.3461
CHARLWOOD 23/10/2020 09/10/2020 14 51.15 -0.2333
CHIVENOR 05/10/2020 11/11/2020 -37 51.089 -4.149
YEOVILTON 07/10/2020 23/10/2020 -16 51.006 -2.64

Ten top tips for phoma management

  1. Select varieties with strong resistance to diseases, including phoma (see the AHDB Recommended Lists).
  2. During autumn, monitor oilseed rape for phoma leaf spots (prioritise susceptible varieties and backward crops).
  3. Look on the underside of leaves; if white tufts (mycelium and spores) are present, the symptom is downy mildew, not phoma.
  4. Note that crops usually start to breach treatment thresholds in October.
  5. A fungicide applied as close as possible to a threshold helps maximise its effect.
  6. AHDB fungicide performance data includes information on product efficacy against phoma.
  7. Treat varieties with lower resistance ratings for stem canker (7 and below) and backward crops first, when 10–20% of plants have phoma leaf spot.
  8. Only treat varieties with high resistance ratings for stem canker (8 to 9) if more than 20% of plants have phoma leaf spot.
  9. When reinfection occurs, consider a second spray – typically, four to ten weeks after the first spray.
  10. Adjust spray programmes to account for any late-autumn fungicide (November) required for light leaf spot control.
How to manage phoma leaf spot and stem canker in oilseed rape
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