Unusual weather conditions lead to challenging decisions on grass weed control

UK - October 06, 2006

Winter oilseed rape crops in Lincolnshire and Nottinghamshire need treating with a grass weed killer as soon as possible, says agronomy company Cropwise. 

Andy McMunn, based at Cropwise’s Newark office, reports that the hot summer and early autumn is having a significant impact on winter oilseed rape grass weed control choices.  Black-grass and other grass weeds are growing away far quicker than usual due to recent warm, moist conditions combined with low dormancy in black-grass resulting from very hot weather during grain ripening.    

“We are seeing very high germination levels of grass weeds which are growing unusually fast, especially where low oilseed rape seed rates are giving less crop competition. These crops need a graminicide such as Aramo right now to tackle the very early weed competition. Delay using Quaver (propyzamide) until later in the season as conditions are not suitable for its use yet,” says Mr McMunn. 

The early graminicide will reduce weed competition from volunteers and brome grass present as well as some of the black-grass.  But Mr McMunn emphasises that most black-grass, depending on its resistance type and the graminicide used, will not be controlled.   

“Using Quaver later will control more than 95% control of all strains of resistant black-grass.  Application should be delayed until the soil is moist down to a depth of at least 5 cm, and the soil temperature is below 6ºC.  These conditions are usually reached in early November, when Quaver should be applied at the full 2.1 l/ha rate with the addition of a graminicide.” 

The Pesticides Safety Directorate recently restricted dims and fops to two sprays of different active ingredients per crop to reduce the spread of resistance in black-grass. For both efficacy and to stay within the rules Mr McMunn suggests Aramo is used early and followed with a Raptor + Quaver mix.