Sugar beet varieties tolerant to ALS-inhibiting herbicides: A novel tool in weed management

The main aim of the present study was to evaluate benefits of the new technology of sugar beet varieties tolerant to foramsulfuron (FSN) + thiencarbazone-methyl (TCM) herbicides commercialised as Conviso® Smart (four weed management strategies were tested) compared to conventional herbicides (two weed management strategies). Plot-field trials were carried out in Prague (Czech Republic) in 2016–2019. Efficacy on Chenopodium album L., Amaranthus retroflexus L., Echinochloa crus-galli (L.) P. B., Abutilon theophrasti Med. and weed beet were evaluated.FSN + TCM controlled all tested weeds very well (efficacy more than 97%) in case of split application with an oil adjuvant. When only one application of FSN + TCM was performed in dry weather conditions, efficacy on C. album and A. theophrasti was insufficient (less than 90%). FSN + TCM fully controlled weed beet at all tested weed management strategies in all experimental years and a residual activity of this herbicide did not allow new plants to emerge. The conventional tank-mixes (TM) controlled C. album and A. retroflexus well (efficacy more than 96%). Efficacy of conventional TM on E. crus-galli ranged from 78 to 100%. Efficacy on A. theophrasti was affected by herbicides used and weather conditions, but did not exceed 92% with either of the conventional TM. The tested conventional herbicides were not able to control weed beet.A relatively high reproductive ability of C. album and A. retroflexus (13,000–157,000 and 7000–10,000 seeds m⁻², respectively) was seen in plots where these weeds were not fully controlled. The seed production of A. theophrasti was relatively low (not exceeded 25,000 seeds m⁻²). However, mature seeds were present in most plots. The reproductive ability of E. crus-galli in sugar beet canopy was much lower (200 - 1800 seeds m⁻²) compared to the other species, due to its late emergence. Weed beet competed with sugar beet only when other weeds were controlled and weed beet survived the treatment. In these plots, fruit production of weed beet was significantly higher (5000–75,000 fruits m⁻²).The highest sugar beet yields (78–100 t ha⁻¹) were in weed-free plots or plots with a low weed infestation (split application of FSN + TCM). A significantly lower yield (45–52 t ha⁻¹) was recorded when C. album and A. theophrasti were not sufficiently controlled. In plots where the weed beet was the only weed not controlled, sugar beet yield ranged from 23 to 61 t ha⁻¹. The lowest sugar beet yield (less than 10 t ha⁻¹) was observed in untreated plots where mainly C. album and A. theophrasti predominated. There was a negative relationship between sugar beet yield and total weed biomass.