Effect of herbicides and soil moisture on weed control,yield and quality of sugar cane (saccharum officinaruml) at Kilombero, Tanzania

Abstract

Field experiments were conducted at Kilombero Sugar Company estate one under rainfed and another under rainfed plus supplemental irrigation condition to evaluate the effects of herbicides on weeds and sugarcane (Saccharum officinarum L) yield and quality. Experiments were laid out in a randomized complete block design with four replications. Plot sizes of 5.8 m x 4 m were used. Treatments were Volmazone (2-(2-chlorobenzyl)-4,4- dimethyl-1,2-oxazolidin-3-one) at 2.9 and 3.8 kg a.i ha-1; Acetochlor 2-chloro-Nethoxymethyl- 6-ethylaceto –o-toluidide at 4.5 and 6.0 kg a.i ha-1 and Metribuzin 4-amino- 6(1,1-dimethyl)-3-Methilthio-1,2,4 triazin-5(4H) 6.0 and 7.5 kg a.i.ha-1. Which were applied as early post emergence. These were compared with weed free check which was hand weeded every two weeks and untreated check. Results revealed that there was significant difference between herbicides treated plots as compared to unweeded check plots (p < 0.05). There was no significant difference between herbicide treated plots and weed free check. All herbicides were effective in controlling grasses and broadleaf weeds to an acceptable level above (90%) up to 8 WAT for both irrigated and rainfed crop, a period which is quite satisfactory for sugarcane. There were variable herbicide treatment effects on individual grass weed species. Itchgrass was best controlled by Volmazone, while Leptochloa and Echnochloa spp were best controlled by acetochlor and metribuzin. Almost all herbicide treatments were ineffective incontrolling nut sedges the control was bellow an acceptable level 90%, although were significant (p < 0.05) as compared to unweeded check. There was a significant difference in sugarcane yield tons ha-1 between herbicides treated plots as compared to unweeded check plots (p < 0.05) for both irrigated and rainfed experiments,but no significant difference in sugarcane yield was observed between herbicide treated plots and weed free check (p < 0.05). For the irrigated experiment, the treatment with acetochlor 4.5 kg a.i ha-1increased yield by 74.7 % which was higher than all other treatments. Other treatments, volmazone 3.8 kg a.i ha-1; metribuzin 6.0 kg a.i ha-1;volmazone2.9 kg a.i ha-1; metribuzin 7.5 kg a.i ha-1; weed free check and acetochlor 6.0 kg a.i ha-1 increased yield between 37.8 and 57.3 % compared to unweeded check. For the rainfed experiment, treatment with acetochlor 4.5 kg a.i ha- 1increased yield by 50.0 % and other treatments that is acetochlor 6.0 kg a.i ha-1; metribuzin 6.0 kg a.i ha-1; weed free check; metribuzin 7.5 kg a.i ha-1; volmazone 3.8 kg a.i ha-1 and volmazone 2.9 kg a.i ha-1 increased the yield of sugarcane between 40.3 and 48.8 % over unweeded check. Both irrigated and rainfed experiments sugarcane yields tons ha-1 positively correlated with number of millable stalks population (r = 0.834 and 0.942) respectively. Different treatments of herbicides had no effect on sugarcane quality parameters (P < 0.05). Economic analysis showed that the highest net benefit and marginal rate of return of 1124.2% was achieved by treatment with volmazone at 2.9 kg ai ha-1for irrigated experiment and for the rainfed experiment the highest net benefit and marginal rate of return of 412.3 % was achieved by treatment with acetochlor at a rate of 4.5 kg a.i ha-1.