Determination of the active growth state of weeds may lead to more reliable predictions of herbicide efficacy. Experiments were conducted at Lacombe and Lethbridge, Alberta, Canada, from 1996 to 1998 to determine if wild oat leaf extension (growth) rate could be used to predict the efficacy of imazamethabenz and ICIA 0604. As expected, wild oat control increased and wild oat biomass decreased with increasing imazamethabenz and ICIA 0604 rates. Mean wild oat growth rates ranged from 6 to 44 mm over a 24-h time interval. Wild oat control at 25% of the recommended doses of ICIA 0604 or imazamethabenz increased as wild oat growth rate increased. However, wild oat growth rate did not influence herbicide efficacy at higher herbicide rates. Regression analysis confirmed that wild oat control at the lowest application rates increased 6 or 14% for every 10 mm of wild oat growth during the 24 h preceding herbicide application of ICIA 0604 or imazamethabenz, respectively. Covariance analysis confirmed the influence of wild oat growth rate on wild oat control by imazamethabenz but not by ICIA 0604. Monocot leaf extension rates may be useful for predicting herbicide efficacy in integrated weed management or decision support systems.
Nomenclature: ICIA 0604, 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-cyclohex-2-enone (proposed common name: tralkoxydim); imazamethabenz; wild oat, Avena fatua L. #3 AVEFA.
Additional index words: Active growth, integrated weed management, predicting efficacy, reduced rates.