What to consider before you spray KERB / ASTROKerb this season

OSR in autumnDow AgroSciences are saying that growers should be getting ready to apply ASTROKerb® (propyzamide and aminopyralid) and Kerb® Flo 500 (propyzamide) to winter oilseed rape. Rape crops have been developing rapidly and most are well past the 3 leaf stage. Most advanced crops have 10 leaves. Even when canopies are dense, excellent blackgrass control can be achieved with these herbicides.

Soil temperatures at 30 cms are cooling – but need to be around 10ºC and falling. In Scotland and the North of England soil temperatures are close – just above 11ºC and colder weather is coming in now, with many places experiencing the wintery weather with the first frosts of the year.  “With blackgrass taking its time to emerge, we need to maximise the persistency of the propyzamide active ingredient and the way to do this is to wait for cooler conditions. At cooler temperatures the herbicide breaks down more slowly and so its activity lasts longer throughout the weed germination and early growth period. The half-life of propyzamide at 10ºC is around 100 days whereas at 15ºC the half-life falls to 60 days,” explains Peter Waite of Dow AgroSciences.

He also warns growers how important it is to be keep Stewardship top of mind. “If you can travel, Kerb or ASTROKerb may be applied after taking all the necessary precautions to avoid contamination of water. But avoid application to frozen ground where subsequent rainfall could result in run-off.”

This autumn these blackgrass herbicides can be tank mixed with a wide range of fungicides for Phoma and/or Light Leaf spot control. This autumn Phoma has come early into susceptible crops and some first Phoma sprays have already been applied. Light Leaf spot is at moderate risk this year. Kerb and ASTROKerb can be tank-mixed with metconazole, prothioconazole (mix Kerb first), prochloraz, mancozeb, penthiopyrad + picoxystrobin and difenconazole and with the following tank mixes where continuous agitation is needed, prothioconazole plus pyrethroid insecticides, tebuconazole, prothioconazole + tebuconazole, procloraz + tebuconazole.

“A tank mix with your chosen fungicide and Kerb or ASTROKerb will probably be the second Phoma spray but the first Light Leaf Spot spray in the programme. But you have until the 31st January to apply Kerb or ASTROKerb, so there is still plenty of time,” he says.

Growers should use the Dow AgroSciences traffic light weather system on the Dow AgroSciences main web site (http://uk.dowagro.com/kerb-weather-data/-) and also on the Farming On-Line web site. The traffic light system indicates, down to individual postcode level, when soil conditions are getting close to the optimum for the application of these post-emergence herbicides. Peter says “This year emoji’s have been added for wind and rainfall to give a more complete picture. We want the system to be more accurate and user friendly for growers and advisors.”

“Growers enter their postcode and the system lets them know whether soil conditions are getting close to the optimal for applying ASTROKerb or Kerb Flo 500. If the traffic light shows red, conditions are not right so don’t apply these herbicides; if amber, soil conditions are closer, so get set to apply and if green, soil conditions are close to becoming right. The system is a strong indicator for growers to look carefully at conditions for any particular field or farm,” explains Peter.

“To optimise ASTROKerb and Kerb’s performance, there are two other areas in addition to soil temperature to consider – soil moisture and weed seed depth. “Soil moisture distributes the herbicides evenly in the top few centimetres of the soil. Soils must not be waterlogged or saturated. Care must be taken to avoid any risk of contamination to water. Germinating weed seed should not come from any deeper than 5 centimetres as the black-grass would be germinating below the zone where ASTROKerb and Kerb Flo 500 concentrations are high enough to give good levels of weed kill,” he advises.

ASTROKerb and Kerb Flo 500 have the same conditions of application and the same wide application window of four months, through to the end of January.  “ASTROKerb delivers the same weed spectrum as Kerb Flo 500, with the addition of key weeds such as mayweed species and common poppy. We would expect activity on sow thistle and groundsel too.” In my experience, says Peter, conditions are normally optimal for application during November.