Field observations of the contact herbicide Atlantis (iodosulfuron-methyl-sodium + mesosulfuron-methyl) plus BioPower indicate that its performance was improved when Auxiliary (prosulfocarb and clodinafop-propargyl) was added to the mix. Weed expert John Cussans of NIABTAG has seen the performance of this mix for a number of seasons in field trials and has observed that the addition of Auxiliary appeared to be better than other herbicides. “The benefit we saw was disproportionate to what we would have expected.”
His theory was that the formulation of Auxiliary contributes as an extra wetting agent. “The combination of Atlantis and Auxiliary is definitely a good option. In one particular trial spring-applied Atlantis + BioPower applied to resistant black-grass at the beginning of tillering – so quite a challenge - gave around 30% control; the addition of Auxiliary doubled this – quite remarkable! This level of enhancement was not seen with other partner herbicides.”
This observation in the field prompted work to be done in the lab to see if the additive effect could be repeated. “We wanted to understand what was happening and whether it was repeatable,” says John.
Trials by Silsoe Spray Applications Unit were then set up to answer the question ‘Why does Auxiliary work so well with contact herbicides?’ Clare Butler Ellis of NIABTAG reports that this lab work showed that Auxiliary boosted the amount and the speed of uptake of Atlantis into black-grass plants, by increasing droplet spread by greater than 10% across the leaf blade, leading to better coverage of the target weed.
“It also increased the solubility of both active ingredients in Atlantis. The addition of Auxiliary to Atlantis + BioPower reduces crystalline deposits forming on the leaf surface which tends to indicate solubility has improved. This translates to a 30% increase in uptake of iodosulfuron-methyl (in Atlantis) and 10% increase in mesosulfuron (the 2nd a.i. in Atlantis),” she says.
She explains that the hypothesis was tested to firstly develop an understanding of the qualitative assessment of leaf surface interaction after droplets are applied and secondly to understand the effect of varying tank mix on the uptake of the active ingredients in Auxiliary into black-grass plants over a period of 24 hours. “Atlantis + BioPower tank mix was compared to two tank mixes - Auxiliary and also Topik plus Defy,(the two active ingredients in Auxiliary.)”
“Photographic images were taken over a period of time after an application of a droplet to individual leaves to see how the liquid behaved on a black-grass leaf. Droplet spreading was significantly improved with the presence of Auxiliary in the tank mix. However, after the droplets had dried, there were clear deposits of crystallized chemicals remaining on the leaf with Atlantis + BioPower tank mixes which were not visible when tank mixes with added components were used. The chemical matrix with the additional constituents appeared to improve the solubility of Atlantis,” Clare explains.
Dr Butler Ellis explains that this evidence is supported by the uptake of both iodosulfuron-methyl sodium and mesosulfuron-methyl into the plant. “Both active ingredients in Atlantis gave an improved uptake by black-grass in the presence of Auxiliary, or Topik and Defy, over the 24 hours monitored in 3 time slots. The rate of uptake of these actives was greatest over the first 5 hours. After 24 hours, 55% of the iodosulfuron-methyl sodium and 98% of the mesosulfuron-methyl was taken up, when Auxiliary was in the tank mix. Without this only 26% and 88% were taken up respectively.”
“The post-emergence graminicide Atlantis (iodosulfuron-methyl sodium + mesosulfuron-methyl) + BioPower is widely used in winter wheat, but its performance has declined over the years on farms where ALS resistance has developed. Auxiliary has consistently been the best tank mix partner for either Atlantis or Unite (pyroxsulam + flupyrsulfuron-methyl-sodium) across a range of trials and field scale operations carried out by a number of organisations including BASF, AICC, Dow AgroSciences and NIABTAG. Research shows that even though black-grass has high levels of ACCase resistance in the UK, the addition of Auxiliary gives significant benefits in terms of black-grass control,” says Iain Ford, Agronomy Manager of BASF.
