Time to apply post-emergence herbicides in winter oilseed rape

Soil temperatures are now under 10°C which makes it ideal for the use of Kerb Flo 500, assuming travelling is possible, according to Dow AgroSciences. Conditions are ideal for herbicide performance as they enable optimal and longer herbicide persistence with enough moisture to get the product to the root zone of the weeds.

David Roberts of Dow AgroSciences says that the usual spray window for Kerb Flo 500 is November and December, but before rushing out to spray, crops must have three true leaves. “We are seeing quite a variation in crop sizes across the country, with some crops being less developed. If that is the case, just wait for them to get to the right growth stage before applying Kerb – the cut-off date for propyzamide is the end of January so you still have plenty of time to control black-grass, meadow-grass or rye-grass in winter rape.”

David reports that there are also many advanced crops and recent research work has demonstrated that leaving Kerb 500 Flo applications until later in the season when canopies are larger has no detrimental effect on black-grass control.

"There may be some concern that larger crop canopies could in some instances intercept the herbicide spray and so interfere with its application to the top 5 cms of the soil where it is needed to control weeds. This is an area that we have been working on in direct response to questions from the field last year. In fully replicated field trials, the level of black-grass control was compared in crops where canopies were artificially removed to crops where the canopy was left intact. This research showed that there was no significant difference between the levels of black-grass control achieved by Kerb Flo 500 between canopy sizes.”

"This latest research demonstrates scientifically that a full oilseed rape crop canopy at time of application makes no difference to the final levels of black-grass control when using Kerb Flo 500. Waiting for optimal soil conditions to be reached remains the correct approach, regardless of ground cover by a well-developed crop canopy,” he says.

David reminds growers and advisors that, in order to get the best from Kerb Flo 500, applications should be made when soil temperatures fall below 10°C and are falling and when the soil moisture deficit is below 50mm and falling. “Meeting these criteria will result in improved residual control, particularly important this year when black-grass germination is prolonged. However care must be taken to avoid any risk of contamination to water and importantly all aspects of good Stewardship must be applied. In waterlogged situations some plant loss may occasionally occur due to shallow rooting however. You can apply Kerb Flo 500 in frosty conditions, but avoid application onto frozen ground where subsequent rainfall could result in run-off into watercourses.”

Dow AgroSciences support a range of herbicide and fungicide tank-mixes to speed up spray operations in a difficult autumn. “Extensive trials data shows that in high populations of difficult black-grass, superior control can be achieved by adding a fop/dim graminicide such as cycloxydim (Laser) to Kerb Flo 500 (even when fop/dim resistance is known to be present) over and above a carbetamide/propyzamide sequence.”

David Roberts points out that the new formulation of Kerb Flo comes in 10 litre packs with self-seal caps and no foils, making it easier and quicker to use and lowering the risk of point source contamination. “The new top dose rate is 1.7 l/ha, meaning fewer packs to open, rinse, clean and then dispose of, making the whole spray operation quicker.”