Using chemical seed dormancy breakers with herbicides for weed management in soyabean and wheat

Summary Variable dormancies result in periodicity in the germination of weeds and make weed control a repetitive practice. Under some conditions, repeated applications of selective herbicides can lead to the dominance of perennial weeds like Cyperus rotundus . Our hypothesis was that applying a chemical dormancy breaker ( DB ) plus herbicide mixture would better control a mixture of weed species. Three experiments were designed to develop a cost‐effective DB treatment and to evaluate its dose with herbicides tank‐mixtures for effective weed management. KNO 3 and gibberellic acid GA 3 as dormancy breakers offered comparable effects, but KNO 3 was more economical than GA 3 . KNO 3 at a 6% concentration was more effective in promoting weed germination than a 3% concentration in soyabean. A combination of KNO 3 (6%) and pre‐emergence pendimethalin 0.75 kg a.i. ha −1  + imazethapyr 0.10 kg a.i. ha −1 controlled annual weeds by 99% and reduced C. rotundus growth by 83%. This treatment gave significantly higher soyabean yield and net returns. Similarly, a tank‐mixture comprising of clodinafop 0.06 kg a.i. ha −1  + metsulfuron 0.006 kga.i. ha −1 was more effective against weeds than pre‐emergence tank‐mix application of pendimethalin 0.75 kg a.i. ha −1  + carfentrazone‐ethyl 0.02 kg a.i. ha −1 and isoproturon 0.75 kg a.i. ha −1 . The use of pre‐emergence tank‐mixture of pendimethalin 0.75 kg a.i. ha −1  + imazethapyr 0.10 kg a.i. ha −1 should exhaust seed/tuber bank if repeated and reduce the application cost of herbicides by 50% and the dose, residue and cost of pendimethalin by 25%.