Eureka! Institutional Repository

The cultivation of lavender (Lavandula angustifolia Mill.) has been growing continuously in Greece over the past 10 years. The most important problem in its cultivation is the weed control because there are no registered herbicides. In addition, the potential selectivity of the available herbicides is unknown. In a 3-year field experiment established at the farm of the University of Thessaly (Larissa), phytotoxicity of various post-emergence herbicides with different mechanisms of action on lavender was assessed. Each year, herbicide applications were made during the breakdown of vegetation development of lavender (late winter). The herbicide treatments included dicamba, clopyralid, aclonifen, imazamox, metribuzin, bromoxynil, tribenuron plus mecoprop, and iodosulfuron plus mesosulfuron at their recommended rates, as well as two untreated (weedy and weed-free) controls. The application of the herbicides was carried out with a precision sprayer adjusted to apply 300 L/acre with a pressure of 2.8 atm. The experimental pattern was that of the complete groups in a free layout with 4 replicates and the size of the test pieces was 3 x 4 m. The phytotoxicity of the herbicides in the crop was assessed by recording macroscopic symptoms at 2, 4, 6 and 8 weeks after application, and by comparing the fresh and dry weight of the drug at harvest. In addition, the yield of essential oil was also evaluated. The herbicides evaluated did not cause visible symptoms of phytotoxicity in lavender during the three years of the experiment. However, the metribuzin herbicide caused a 23% to 28% decrease in the essential oil yield, while the oil yields of the other chemical treatments did not differ from that of the untreated weed-free control. In general, the presence of weeds reduced the essential oil yield of lavender by 75%. No differences in essential oil constitutes were detected among controls and chemical treatments.