Weed control in potatoes (2008-2009)

The work was commissioned in response to changes in the availability of herbicides for use in potatoes as a result of pesticide regulatory changes (withdrawal of paraquat and introduction of reduced rates of linuron).

This project evaluated the efficacy and crop safety of herbicide programmes based on alternatives to paraquat and higher rates of linuron.  The evaluations were based on a series of six replicated small plot trials undertaken during 2008-2009 in the east of England.  This period consisted of two, very dry springs, which allowed good comparison of contact herbicides but did not provide good soil conditions for the comparison of efficacy and crop safety of residual herbicides.

The contact herbicides Basta (glufosinate), Retro (diquat) and Shark (carfentrazone) were compared with paraquat + diquat (PDQ) in terms of weed control and crop safety.   

 The reduced rates of linuron (1.2l/ha), were shown to contribute very useful levels of grassweed and BLW control but in no situation did this rate provide sufficient residual weed control alone.  In 2009, early applications of Stomp (pendimethalin), in programme with other herbicides applied at crop emergence, were evaluated to look for more effective polygonum weed control.  

The suitability of Sencorex (metribuzin) as a partner for linuron (1.2l/ha) posed questions about crop safety on lighter soils.  To answer such questions, a range of Sencorex rates (0.25kg/ha – 1.5kg/ha) was applied to a loamy sand in 2009.  No crop effects were observed.  This was almost certainly due to a dry spring and the results should not imply similar levels of crop safety in a spring with normal rainfall.

 The work highlighted the need for more complex mixtures of herbicides necessary to provide adequate contact / residual activity and maintain broad-spectrum weed control.