Efficacy and selectivity of pre-em herbicide on dependence of soil types and precipitation in sunflower crop

Abstract

During the growing seasons in 2018 and 2019, two field trials were conducted to estimate how precipitation affects the efficacy of PRE-em herbicides in sunflower crop grown on different soil types. Both regions were naturally infested with a high population of Polygonum aviculare L., Solanum nigrum L., Chenopodium album L., Amaranthus retroflexus L., Portulaca olearacea L. and Echinochloa crus-galli (L.) P. Beauv. Efficacy of PRE-em herbicides varied among weed species, treatments, periods of efficacy estimation, regions and years, respectively. Overall performances of the PRE-em herbicides were correlated with the weather and soil properties. Humid April in Bitola region in 2018, particularly the first week after application (34 mm) before weed emergence caused herbicide leaching from the soil surface, which probably was the most likely reason for the lower efficacy of PRE-em herbicides in 2018, compared to their application in 2019. In 2018 precipitation above 30 years average were recorded in the Titov Veles region as well, but due to their equal occurrence particularly during the first and second week after application, as well as soil type properties (higher content of clay and organic matter) leaching did not occur and efficacy was good to excellent. Contrary, the limited precipitation after PRE-em application (five, nine, and eight mm during the first week before application, first and second week after application) may have contributed to the poor performance of PRE-em herbicides in the Titov Veles region in 2019 compared with 2018. Heavy precipitation directly following PRE-em application caused sunflower injury in the Bitola region in 2018, which ranged from 9–28% across PRE-em treatments seven days after application. Injures of oxyfluorfen and dimethenamid were more serious (24 and 28%, respectively). Sunflower yields for each treatment in both region s generally reflected overall weed control and crop injury.

Keywords

• weeds
• herbicides
• sunflower
• efficacy
• selectivity
• soil
• precipitation