Assessment of the crop safety of post-emergence herbicides in a range of potato varieties (2012-2013)

The tolerance of twenty widely grown potato varieties to post-emergence applications of metribuzin, bentazone and a tank mixture of rimsulfuron and metribuzin was assessed. Two trial sites were established in both years (2012 and 2013), one in Staffordshire and one in Lincolnshire.

The degree of damage from metribuzin is closely related to potato variety.  Lower rates of metribuzin resulted in generally lower levels of crop damage but some varieties show very low tolerance to metribuzin, regardless of the rate applied e.g. Maris Piper, Innovator, Cabaret, Estima and Harmony. The lower rate of metribuzin usually resulted in more transitory damage compared to the higher rate of application.

No manufacturer guidelines, for tolerance to bentazone, existed for many of the varieties tested in the project. Crop damage from bentazone was more general across varieties, although some varieties were severely affected e.g. Markies, Lady Rosetta, Desiree, King Edward, Charlotte and Fontane.  Some varieties showed initial damage which later proved to be transitory.  

Overall, a level of crop damage should be expected for all combinations of post-emergence herbicides and potato varieties.  Results from this project will help with decision-making where a grower/agronomist is faced with weighing-up the effect of weed competition versus herbicide damage on crop yield. Both the initial severity and persistence of symptoms should be used to gauge potential crop yield reduction.