عنوان مقاله [English]
Introduction: Sugar beet competes with weeds for light, nutrients and water resources and is so sensitive especially at the early stages of growth. Weeds are the most important factors limiting sugar beet production in Iran. Although, about 20 herbicides were registered to control weeds, but their effectiveness would be high only if farmers use them properly. Due to sensitivity of weeds to herbicides at certain times, determination of the best herbicide application time is very important. Cloridazon is one of the selective herbicides registered for broadleaf weeds control of sugar beet. Both pre and post-emergence applications of this herbicide were recommended but the effectiveness of treatment should be evaluated.
Material and Methods: In order to determine the best application time of Cloridazon (Pyramin, WP 65%) to control broad leaf weeds in sugar beet field, an experiment was conducted in two locations i.e. Golestan province (Gonbad station) and Khozestan province (Safiabad, Dezful station), Iran, during 2018. Experiments were arranged as randomized complete block design with 4 replications. Treatments were: application of Cloridazon at 3, 4 & 5 kg/ha, and two different application times (i.e. pre-emerge and post-emerge at 4 leaf stages), application of Phenmedipham+Desmedipham+ Ethofumesate (Betanal Progress O.F. at 3 lit/ha at 2-4 leaf stages), and weed free as the check. Each experimental plots were divided into two parts including: uncontrolled part (as weedy control) and treatment part. Efficacy of the treatments on weed population and control was evaluated based on the percent of reduction in weeds density and dry weight and EWEC scoring system at 30 days after herbicides application. Root yield of sugar beet was also measured at the end of the growing season. The weed spectrum was not similar in both locations. Polygonum aviculare and Sonchus arvensis were dominant in Gonbad and Malva sylvestris and Sinapis arvensis were dominant in Dezful. Experimental data were analyzed by SAS (version 9.1) program and means were compared with the Duncan's multiple range test.
Results: The results indicated that the effects of treatments on weeds were significant. Application of Cloridazon at 3 kg/ha controlled sinapis arvensis by 95 to 100% and Sonchus arvensis by 86 to 93%. In both locations, the difference between this treatment and Phenmedipham+ desmedipham+ ethofumesate (Betanal Progress OF) was not significant. Chloridazon (as pre-emergence treatment) performed better in controlling broad leaf weeds compared with post treatment. The pre-emergence application of Chloridazon (at 3 , kg/ha) was the best treatment (with more than 85% weed population control) in both studied areas. In addition, this treatment had no significant difference with Phenmedipham+ desmedipham+ ethofumesate (Betanal Progress OF). The results show the low efficacy of Pyramin on weeds when it was applied late (after 2 leaf stages). However, due to different germination time of weeds, single application of Pyramin is not enough to achieve the desired results. Application of post-treatments (like Betanal Progress OF) is necessary as complementary treatments. However, using 3 kg/ha of Pyramin, cannot control Malva sylvestris if this weed is dominant in the field, and the Pyramin dose should be increased to 4 kg/ha. Anyway, application of Chloridazon at more than 4 kg/ha is not recommended as it would have negative effects on sugar beet seed germination. It should be noted that both cultivars (Roza Gold and Silvetta) used in Gonbad and Dezful were monogrm and more sensitive to herbicides with respect to polygerms. The probability of seed damage on monogrm cultivars will be higher by pre emerge herbicide application. Based on our results, application of Chloridazon (at 3 kg/ha as pre-emerge treatment) was the best treatment for sugar beet root yield and showed no significant difference with the application of Phenmedipham+desmedipham+ ethofumesate (Betanal Progress OF).