Phoma control information now available

Phoma leaf spot is already appearing in oilseed rape and will soon require treatment.

The latest HGCA fungicide performance trials show that a range of fungicide products can provide good control of phoma leaf spot and stem canker.

Phoma can be a problem for rape crops throughout autumn and winter. Early epidemics in the first half of October or earlier are most damaging and typically put 0.5 t/ha yield at risk. Fortunately, conditions this year have prevented early epidemics from occurring. According to Dr Peter Gladders, Plant Pathologist at ADAS, “We are heading for an average year regarding the development of phoma, very few crops have reached the control threshold but do have the first spots.” Now is a vital period for monitoring crops so that fungicides can be applied at the optimum time.

HGCA trials found that good control is possible with two sprays at half dose. Correct timing of the sprays is a key part of getting the best control. The first spray should be made when 10–20 % of plants have phoma leaf spot, the second when there are visible signs of reinfection.

When choosing a control product it is important to take other effects into account. Curative activity is possible with flusiazole and prothioconazole-based fungicides. Metconazole and tebuconazole-based products also act as plant growth regulators.

Farmers should also be aware of late epidemics which happen from December onwards and are especially damaging to smaller plants. Many parts of the UK have experienced a difficult start to the growing season with slow plant development, as a result, late epidemics could be an issue later this year.

Full details of fungicide performance in oilseed rape, wheat and barley will be presented at the Agronomists’ Conference in Peterborough on 11 December.