Influence of climatic conditions and plant physiology on glufosinate-ammonium efficacy

Under field conditions the efficacy of glufosinate-ammonium on Galium apari ne L. is quite often variable. Experiments under controlled conditions with G. aparine and the more susceptible species Brassica rapa L. showed that e specially low relative humidity (r.h.) and low light intensity reduced the accumulation of ammonia in the plants and glufosinate-ammonium performance. As the light intensity under field conditions always exceeds the intensiti es applied in the experiments this parameter may not be of practical import ance. In contrast, low r.h. often occurs under field conditions and could e xplain the variable G. aparine control. A retention study showed that reten tion on G. aparine was significantly higher than on B. rapa but ammonia acc umulation in the plants indicated that glufosinate-ammonium uptake by G. ap arine was lower than that by B. rapa. Glufosinate-ammonium performance was improved on both species by adding ammonium sulphate to the spray solution; however, the increase in efficacy by ammonium sulphate was two times highe r for G. aparine than for B. rapa. Ammonia accumulation in untreated plant parts after glufosinate-ammonium application indicated some translocation o f glufosinate-ammonium in B. rapa but none in G. aparine.