Good potato quality samples will be hard to achieve this year and now, when the weather is cooler and wetter, foliar and tuber blight has become a real threat in many areas. Consequently Dow AgroSciences are advising growers to make sure that they keep the blight protection going and invest in sprays with tuber blight protection, such as Electis, that are physically compatible with desiccants.
Desiccating potatoes whilst maintaining tuber blight protection right to the end of harvest has become more complicated with the trend to split dose desiccation treatments and the need for adding adjuvants to certain blight fungicides. Whatever haulm destruction method is preferred, it is essential to maintain effective protection against tuber blight right up to the time the haulm has died and lifting has started, especially this year when conditions are optimal for tuber blight infection, advises Andy Leader, Principal Biologist for Dow AgroSciences.
"Mature potato foliage and stems are an active source of zoospores. These drop off or are washed into the soil through which tubers will be lifted. An effective blight programme that prevented zoospore production in the first place should be used, but this protection must extend right throughout the desiccation process so that the risk of blight infection is reduced as far as possible.
The trend towards split applications of desiccants, with the first spray opening up the canopy and the second spray desiccating the crop more thoroughly, has complicated this process. Using split treatments can mean that the crop is exposed to blight infection for a longer period of time and could increase the risk of tuber blight overall. MORE……………..
"The choice of fungicides late on in the programme makes a significant difference in the overall fight against tuber blight and in the quality of the end sample. Growers should use products with known, proven zoospore activity and which can be mixed with desiccants." adds Andy.
"Zoxium in Electis stops the formation and release of zoospores. When used in a suitable programme, it protects against tuber blight and it is physically compatible with diquat, glufosinate-ammonium and carfentrazone desiccants, protecting the crop through to lifting. Because of its action, sulphuric acid is not mixed with any blight fungicides or adjuvants. Diquat and glufosinate are not recommended with adjuvants, as this practise could jeopardise crop safety, but they can and should be mixed with blight fungicides with known zoospore activity especially when used in a split dose sequence," concludes Mr. Leader.
Editors Notes : Electis contains 8.3% w/w zoxium and 66.7% w/w mancozeb, formulated as a WDG. It is recommended on all varieties of potatoes at spray intervals of 7 to 14 days. It has a dose rate of 1.8 kg/ha in 200-600 litres of water per hectare. It has a maximum number of treatments of 10 per crop and a harvest interval of 7 days. It is packed in a 3-ha pack (5.4 kg).
