Sunflower is an important oilseed crop worldwide and its successful cultivation requires careful control of weed species. The Clearfield® technology in sunflower has been developed to allow the use of imidazolinone herbicides as a post-emergence weed control option. The Clearfield hybrids are tolerant to imazamox, aherbicide of the imidazolinone group with the trade name Pulsar 40, produced by the BASF Chemical Company. However, after imazamox treatment a temporary yellowing of the meristem tissue of the sunflower leaves is observed. The herbicidal stress increases in combination withun suitable weather conditions such as long term high temperatures and drought.
The aim of the study was to examine the response of Clearfield sunflower hybrids to higher doses of the imazamox herbicide. Five hybrids were examined: LG 56.58, Tektonic, Alego, Meldimi andPrimis. The doses of imazamox treatment were as follows: non-treated control,the recommendable dose of imazamox (4.8 g a.i./da= 120 ml /da Pulsar 40) and doubled imazamox doses (9.6 g a.i. / da = 240 ml/da Pulsar 40). Treatment with the herbicide was done at 4th-6th-leave stage. The biometric and photosynthetic analyzes were carried out after the treatment. The photosynthetic leaf gas exchange, quantum yield of PSII photochemistry and growth parameters (height, fresh weight and leaf area) were determined.
The obtained results showed that the treatment with the recommendable dose of imazamox caused a temporary negative impact on the photosynthetic performance and growth of the sunflower plants, which recovered after 14 days.The doubled dose of imazamox seriously damaged the existing top leaves of the sunflower plants, but the newly developed leaves were without toxicity symptoms. The studied sunflower cultivars expressed good tolerance to imazamox, applied in the recommendable dose.