Hoeing number and time for weed control in sunflower

Abstract

Two field experiments were conducted in the Depressão Central region of Rio Grande do Sul State, Brazil, in order to establish correct time and hoeing number that would best fit the need of maintaining (Helianthus annuus L.) crop free of weed interference. The treatments tested were one, two, or three hoeings, 15 days apart, applied during a 30-day period in the first half of the crop cycle. Results showed that in the first year one hoeing, performed 20 or 35 days after sunflower emergence, was sufficient to maintain the crop free of weed interference, whilst in the second year two hoeings were needed to attain the same effect, the first one applied 15 days after emergence and the second 15 or 30 days later. One hoeing applied 45-50 days after emergence was not effective, since the sunflower plants did not recover from the initial effects of weed interference, resulting in grain yield decrease.