engleski

Abutilon theophrasti Med. sensitivity to topramezone and adjuvants combination

Maize is the most important crop in Croatia with production occurring on 400, 000 ha (i.e. 35% of total arable land) in Croatia. Herbicide use totals 1, 015, 000 kg a.i. in Croatia with maize accounting for 370, 000 kg a.i. In last two decades Abutilon theophrasti (ABUTH) become a very important weed in maize. Although ABUTH is relatively sensitive to topramezone, in some cases its absorption can be reduced due to leaf morphology (hair and epicuticular wax. The goal of this research was to determine the application rate of topramezone that results in 90% ABUTH growth reduction (GR90). Topramezone was applied at 8.25 ; 16.5 ; 33, and 66 g a.i. ha-1 in combination with the following adjuvants: nonionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), urea ammonium nitrate (UAN), ammonium sulfate (AMS) and combinations thereof (NIS+UAN ; NIS+AMS ; COC+UAN ; COC+AMS ; MSO+UAN ; MSO+AMS ; UAN and AMS). A non-treated check was included for comparison purposes. Abutilon theophrasti plants were grown under controlled conditions at the constant temperature of 250C:200C (day:night) with a photoperiod of 16:8 h (light:dark) and a relative humidity of 75%. All herbicide/adjuvant combinations were applied to ABUTH with four to six leaves. Plant shoots were harvested three weeks after treatment to determine biomass weight per pot. An interaction between adjuvant system x topramezone application rate was present for ABUTH biomass. Abutilon theophrasti was sensitive to topramezone even at 33 g a.i. ha-1 applied alone. However, the addition of adjuvants to topramezone increased ABUTH control particularly when combinations of adjuvants were applied (COC+UAN ; COC+AMS ; MSO+AMS ; NIS+UAN and NIS+AMS). The calculated topramezone application rate when applied with selected adjuvants required for 90% ABUTH dry matter reduction was lower than the half the normal topramezone application rate (33 g a.i. ha-1) and ranged from 2.5 g a.i. ha-1 (MSO+AMS) to 21.5 g a.i. ha-1 (NIS).

Topramezone, adjuvants, Abutilon theophrasti, maize

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