East: Watch out for phoma in oilseed rape

Warm autumn days and moist soils have encouraged quick establishment of early September sown wheats and late-sown oilseed rape, although many mid to late September sown oilseed rape crops are still small and vulnerable.

Generally cereal seed-beds are good or reasonable, which should, along with moist soil conditions, help maximise the efficacy of pre- and peri-emergence herbicides. Early completion of these sprays before the target weeds have emerged and started to grow will also improve activity.

If cereals are not treated with an insecticidal seed dressing such as Deter (clothianidin), an insecticide should be applied. Typically this should be at the one to two leaf stage.  This application should be prompt as migrant aphids will be attracted as soon as the field appears green.

Deter will offer six to eight weeks protection. The persistence of foliar sprays will depend on temperature and product, but is typically two to three weeks.  Therefore, a follow up foliar application may be required depending on the length of the autumn season.

In oilseed rape, cereal volunteers and blackgrass continue to emerge and should be sprayed off before becoming competitive with the crop.  As yet, few phoma lesions have been seen, but an early infection is expected following wet conditions during August. 

Continue to monitor crops and treat once a threshold of 10% plants infected is reached.  Extra vigilance and quick reaction is required on smaller plants as there is less distance for the infection to travel before reaching the stem where it is beyond the control of fungicides. 

Typically, phoma sprays are based on flusilazole, difenoconazole or prothioconazole, in a season where early phoma infection is likely it would be wise to choose the triazole with most activity. Even varieties with a relatively high stem canker score respond well to treatment, this would include DK Cabernet and Sesame with Recommended List ratings of 6.

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