Aqueous adjuvant concentrate with improved spray drift properties and method for its preparation comprising the steps of: i) dissolving from 15 to 30% by weight, on the weight of the final concentrate, of ammonium sulfate in water; ii) adding to the solution from 1 to 10% by weight, on the weight of the final concentrate, of anionic esters of alkyl polyglycosides; iii) dispersing in the solution from 2 to 10% by weight, on the weight of the final concentrate, of hydroxypropyl guar or hydroxypropyl guar acetate; iiii) adding ammonium sulfate to the dispersion to reach an ammonium sulfate final concentration comprised between 33 and 40% by weight.