عنوان مقاله [English]
Introduction: Increasing the environmental concerns emerged from the extensive use of herbicides have caused to work and introduce new approaches for their application by weed scientists. Nonetheless, weeds limit crop production especially when herbicides are removed from the weed management strategies. Optimizing herbicide doses, by increasing farmer’s knowledge about various options of herbicide application, is one of the most important strategies for reducing herbicide application. Tank-mixed herbicides, adjuvants, and split application of herbicide are more interesting, users friendly, and effective to implement this approach. Post-emergence herbicides require adjuvants to be tank-mixed or built into the formulation to enhance their performance. Utilizing these methods is very essential for crops which are very weak competiveness against weed, because of herbicides application is a common method in them. Sugar beet is an important crop grown in the most cultivation areas of Iran under cultivation about 82.5 thousand hectares over average yield 42 ton ha-1. This study was done to increase the performance of some post-emergence herbicides for controlling weeds in sugar beet using adjuvants, tank-mixed herbicide, as well as herbicide split-applied herbicide treatments.
Materials and methods: A factorial experiment based on randomized complete block design with three replications was conducted at the research field of Ferdowsi University of Mashhad (985 m altitude, longitude 59˚ 28´ and latitude 36˚ 15´) in 2013. The factors included the method of herbicide application (full and split application), herbicides (chloridazon (5 Kg ha-1) plus desmedipham (6 L ha-1), desmedipham plus phenmedipham plus ethofumesate (3 L ha-1) and chloridazon (5 Kg ha-1) plus desmedipham plus phenmedipham plus ethofumesate (3 L ha-1)), and adjuvants (Non-adjuvant, Adigor (%1.5 v/v), Citogate (%0.2 v/v) and Ammonium sulfate (%0.5 v/v)). Furthermore, two control treatments were considered as weed free and weed infested for each replication. Herbicides were applied with a backpack sprayer equipped with 8002 flat fan nozzles that calibrated to deliver a spray volume of 400 L ha-1 at 275 kPa. Commercial sugar beet seeds, ‘005’ Monogerm provided from Improvement Research Institute of sugar beet, Karaj were planted on April 25 by hand to the depth 2 to 3 cm of the soil. Each plot consisted of four rows of sugar beet spaced 50 cm apart and 5 m long and density of sugar beet was 12 plants per m2. Seedbed preparation operations consisted of moldboard plowing, double disking and application of N at 69 kg.ha-1, P2O5 at 67.5 kg.ha-1 and K2O at 50 kg.ha-1 was done according to the soil test and the fertilizer recommendations. Irrigation was performed once a week. In order to determination of total weed biomass and density, weeds existing in the area 1×1 m2 were collected, counted and weighted. Also sugar beet root yield and biomass was recorded for same area. Data were subjected to ANOVA using the PROC GLM procedure in SAS Version 9.4 and means were compared using Fisher’s protected LSD test at the 0.05 level of significance. Drawing of figures were done by SigmaPlot Version 12.5. The relationship between sugar beet root yield and weed density and biomass were described with hyperbolic decay 2 parameters model.
Results and discussion: In the experimental plots, we observed ten species of broadleaf weeds among which redroot pigweed (Amaranthus retroflexus L.), common lambsquarter (Chenopodium album L.), black nightshade (Solanum nigrum L.), purslane (Portulaca oleraceae L.), and field bindweed (Convolvulus arvensis L.) have higher relative frequency and density than others. The results showed that the highest sugar beet root yield, as value 110.29 ton ha-1, occurred in split application of chloridazon plus desmedipham with Adigor. Furthermore, the highest sugar yield obtained from the plots with split application of chloridazon plus (desmedipham plus phenmedipham plus ethofumesate) with Adigor at 16.10 ton ha-1. In split application of desmedipham plus phenmedipham plus ethofumesate without adjuvant, the lowest sugar beet root yield and sugar yield were recorded 50.07 and 7.57 ton ha-1, respectively. Full application of chloridazon plus (desmedipham plus phenmedipham plus ethofumesate) with Adigor with %17 sugar content, and split application of desmedipham plus phenmedipham plus ethofumesate Adigor with %11.74 sugar content had the highest and lowest, respectively. Split application of chloridazon plus desmedipham with Citogate and full application of chloridazon plus (desmedipham plus phenmedipham plus ethofumesate) with Citogate indicated completely weed control, and full and split application of desmedipham plus phenmedipham plus ethofumesate with ammonium sulfate had the lowest performance of weed control. The results of the regression analysis showed that the highest yield of sugar beet occurred when total weed density or biomass are zero (104.62 and 101.41 tonha-1 were estimated, respectively). Also, when weeds density and biomass increased to 24 plants m-2 or 479.13 g dry matter m-2, the root yield of sugar beet will be decreased by 50%.
Conclusion: The results of this study showed that split application of chloridazon plus desmedipham with Adigor or Citogate, created the highest sugar beet root yield and appropriate weed control among all treatments. In contrast, split application of desmedipham plus phenmedipham plus ethofumesate without any adjuvant had the lowest performance of weeds control. It was concluded that the most important factor among the experiment factors was the type of herbicide or herbicide combination.