Potato Review

44 POTATO REVIEW MAY/JUNE 2020 WEED CONTROL “ e loss of diquat means earlier herbicide application and we will be advocating spraying seven to 10 days after planting once ridges are settled. Contact sprays, such as Gozai or Shark, are limited to no more than 10% emerged, any later and the growth will be seriously checked,” Eric said. “In a later planting season such as 2020 this is time growers can ill a ord to lose. is is a complete change to what growers are used to, as diquat could be applied up to 40% crop emergence.” Post-planting weed control With the dilemma of which product to use as a contact option relatively straightforward to resolve, thoughts will turn to the residual programme, says John Keer, agronomist for Richard Austin Agriculture Ltd. “Residuals remain the best means of post- planting weed control and the most cost- e ective,” he said. “I tend to favour three-way mixes with Sencorex Flow (metribuzin) as the base treatment for its broad spectrum of activity. It also has better activity on weeds that escape either Gozai or Shark.” ose faced with cultivated land that has since baked hard and cloddy, may nd it more di cult to achieve a good tilth, in which case expectations of performance may need to be tempered. In these cases, John would favour a three-way mix to bolster control. “On the silts I opt for a rate of 0.4-0.7 litres/ ha of Sencorex Flow depending on variety and soil texture in combination with Emerger (aclonifen) and Defy (prosulfocarb). Emerger is not a replacement for the higher rates of Linuron, but of the recent introductions it has the best spectrum of control and is more cost e ective too.” Emerger is a residual with a di erent mode of action. As the weed emerges through the soil surface it picks up the active substance on its hypocotyl (broad-leaved weeds) or coleoptile (grasses). “Emerger’s best attribute is the method by which it is taken up by the weed as it is less constrained by soil moisture than other residuals. It’s also probably the best product for control of black-bindweed, although post- emergence treatments will still be required in several situations,” John said. Another change for this season that supports the need for strong product combinations is the extended period of control required as a result of earlier applications. ““The choice of partner products will depend on the weed spectrum present, but because applications are likely to be earlier than most are used to, the weed picture is likely to be less than complete.” Eric Anderson Eric Anderson Scottish Agronomy ➜