Comparison of the effectiveness of flaming and spraying with glufosinate-ammonium in controlling weeds in thyme (Thymus vulgaris L.) sowing

Abstract

The purpose of this four-year study was to compare the effectiveness of flame weeding applied on two dates to that of spraying with glufosinate ammonium in controlling weeds in common thyme grown from sowing directly into the field. Flaming (90 kg propane∙ha–1) was applied immediately before thyme emergence or 6 days later, and glufosinate-ammonium (450 g∙ha–1) was applied on the same date as the first flaming. Emergence of thyme began 15–18 days after sowing, was very uneven and in some years it was extended up to 4 weeks. Thyme seedlings were very fine and their initial growth was very slow, which made them highly sensitive to the competition of weeds. The growth rate of thyme  increased over time, reaching its greatest value in the last ten days prior to harvest, when the plants gained their average height, depending on the year, from 18.3 to 22.4 cm and developed from 17 to 21 first and second order branches. Weeds started to emerge 8–11 days after thyme was sown and about 3 weeks later their number in the control plots varied depending on the year from 175 to 541 pcs.∙m–2. All methods were very effective in controlling weeds immediately after treatment, but had no soil residual activity and soon new weeds emerged. Four weeks later, the most effective method was spraying with glufosinate-ammonium, which, depending on the year, reduced both the number and fresh weight of weeds by 43 to 85%. Flaming applied at the first or second dates controlled 33–59% and 37–68% of weeds, respectively. After first weeding, the differences between compared treatments disappeared. Essential oil content in the grated herb obtained from the control plants ranged from 2.5 to 3.4%. In the oil, a total of 39 compounds were identified, with the number ranging from 33 to 36 in individual years. More than half of the essential oil was thymol and two other important compounds were γ-terpinene and p-cymene.