The loss of diquat to growers in the UK means potato crop desiccation will be a longer and more protracted process, which could increase the risk of late-season diseases such as tuber blight and rhizoctonia.
Rapid burndown of potato haulm was a valuable tool in helping manage disease, by rapidly removing foliage that could be at risk from virus-carrying aphids and blight.
Therefore, disease programmes may need changing for the latter part of the season.
Farmers Weekly asked three specialist potato agronomists for their thoughts on managing disease in crops desiccated without diquat.
John Sarup of Spud Agronomy noted that nitrogen management is of importance. “It is likely that soil nitrogen availability will be on the low side due to the autumn and winter rainfall, so without doing any soil min N testing, we are in the dark. If we apply too much nitrogen, crops will be difficult to kill before harvest, skin set might be delayed and there is a risk of disease – either from late blight or dry rot/gangrene on the back of damage at harvest. Where possible, for maincrop potatoes, I have always preferred to put two-thirds of the N requirement in the base, with the rest going on around tuber initiation. For salads and seed, all go on in the base. It is worth remembering that nitrate N is mainly used by the plant for foliage production. We don’t harvest foliage, so we only need enough to achieve full ground cover and maintain that cover long enough to allow the crop to bulk and achieve the desired size for the market.”
Read the full article in Farmers Weekly here
Photo: Gary Naylor