Soil Moisture critical to grassweed control success

UK - October 07, 2005

For the most effective blackgrass control with Kerb Flo (propyzamide) on winter oilseed rape crops assess your soil moisture, not crop or weed size, says Dow AgroSciences.

"A four-year trials programme with ADAS Boxworth has underlined the crucial importance of soil moisture, down to at least 8 cm, in activating Kerb Flo," says Mr Pollak.  "It may be December before the soil moisture deficit has recovered to that level."   

 Mr Pollak advises growers track weekly Met Office figures and check local field conditions to be sure that soils are uniformly moist.  Kerb Flo can be applied at 2.1 l/ha after the oilseed rape crop has three true leaves, from 1st October through to 31st January. 

Minimal tillage can conserve soil moisture, and it leaves grassweed seeds nearer the soil surface.  Blackgrass, brome and other grassweeds emerging from less than 5 cm down have shallow roots emerging into the Kerb Flo treated zone, resulting in almost total control.  

In fields where 100% blackgrass control is needed, Dow AgroSciences recommends oilseed rape is established with the absolute minimal soil disturbance then rolled after drilling. 

"Experience and trials results have consistently shown the less soil is disturbed the better the weed control," says Mr Pollak.  "We've seen Kerb Flo control blackgrass up to 99% in our minimal tillage experiments, year after year after year." 

He advises that soil moisture is as critical in ploughed fields where Kerb Flo's activity has been shown to increase when applied during late November to December.

Where blackgrass is germinating from depths of below 5 cm Kerb Flo should be complimented in a programme or tank-mix with a contact dim or fop graminicide, even where resistant blackgrass is found. 

"Irrespective of the resistance profile of a field, in our experience, sequencing or tank mixing of dim or fop herbicides with Kerb Flo can enhance overall blackgrass control levels.

"Low soil moisture deficits, the position of grassweed seed after minimal tillage and well-timed Kerb Flo applications are all key factors to consistently achieve the best blackgrass control in oilseed rape," says Mr Pollak.