INTERNATIONAL JOURNAL OF AGRICULTURE & BIOLOGY 1560–8530/2005/07–6–889–891 http://www.ijab.org Determining Suitable Combination of Sorgaab and Pendimethalin for Weed Control in Cotton (Gossypium hirsutum L.) ZAHID ATA CHEEMA 1 , BASHARAT ALI AND ABDUL KHALIQ Weed Science Allelopathy Lab, Department of Agronomy, University of Agriculture, Faisalabad–38040, Pakistan 1 Corresponding author’s e-mail: zahidata@uaf.edu.pk ABSTRACT A field trial to determine the suitable combination of Sorgaab (sorghum water extract) with reduced rates of Pendimethalin for weed control in cotton was carried out at Agronomic Research Farm, University of Agriculture, Faisalabad. Sorgaab @ 12 and 16 L ha -1 was combined with Pendimethalin at reduced rates as 833, 625 and 416 g a.i. ha -1 , respectively and were compared with full dose of Pendimethalin @ 1.25 kg a.i. ha -1 . A weedy check was maintained as control. Results of the study showed that combined spray of Sorgaab @ 12 L ha -1 + 2/3 Pendimethalin @ 833 g a.i. ha -1 showed maximum reduction (85.17%) in total weed dry weight recorded at 45 DAS and was statistically at par with all other treatments except control. Combined spray of Sorgaab @ 16 L ha -1 +1/3 Pendimethalin @ 416 g a.i. ha -1 showed maximum reduction (31.75%) in the total weed dry weight recorded at 65 DAS and was at par with full dose of Pendimethalin @ 1.25 kg a.i. ha -1 . The increase in seed cotton yield was maximum with Sorgaab @ 12 L ha -1 + ½ Pendimethalin @ 625 g a.i. ha -1 and higher by 31.5% than control, and also it was the most economical as compared with other treatments. Key Words: Allelopathy; Cotton; Sorgaab (sorghum water extract); Pendimethalin; Weeds INTRODUCTION Use of allelopathic materials in combination with reduced rates of herbicides is major focus of present research in Pakistan. Sorgaab (Sorghum water extract) is being investigated for this purpose. Several studies conducted by Cheema and associates (Cheema et al., 2002; Cheema et al., 2000; Ahmad et al., 2000; Khaliq et al., 2002) have revealed that weed inhibition with Sorgaab ranged between 40-50% which is less than weed control achieved with herbicides (80-100%). Although herbicides are very effective in controlling weeds yet certain risks as environmental pollution and human health are involved in herbicide use. Use of herbicides require technical know how which is generally lacking in the country. Improper use of herbicides may lead to crop injury, health hazards, soil and water pollution and in certain cases, target weeds are not controlled because of low doses used by farmers. Herbicide resistance in weeds due to continuous use of the same herbicide for several years is also an emerging problem. These problems have opened new avenues of research i.e. identifying new herbicides, utilizing natural and biological control measures and combining and integrating one or more methods of weed control. One approach may be reduction in herbicide usage in combination with allelopathic materials as Sorgaab, which contains a number of allelochemicals, which are mainly phenolic compounds. Cheema et al. (2002) has investigated the possibilities of reducing the herbicide dose in combination with Sorgaab and reported that Sorgaab @ 12 L ha -1 combined with Pendimethalin @ 0.5 kg a.i. ha -1 (reduced by 60%) applied at sowing was quite effective in suppressing the density and growth of Trianthema portulcastrum. In another study, Cheema et al. (2003) found that doses of Pendimethalin and S-metolachlor can be reduced by 67% in combination with Sorgaab. Despite these initial trials, the need still exists to verify the previous results and maximize possible reduction in herbicide dose. This study was, therefore, aimed at determining the best dose combination of Sorgaab and Pendimethalin for weed control in cotton crop under agro- ecological conditions of Faisalabad (Pakistan). MATERIALS AND METHODS The present research was carried out at the Agronomic Research Area, University of Agriculture Faisalabad. The experiment was laid out in RCBD with four replications in plots measuring 7 x 3 m. Sorgaab @ 12 and 16 L ha -1 was combined with Pendimethalin at reduced rates as 833, 625 and 416 g a.i. ha -1 , respectively and were compared with full dose of Pendimethalin @ 1.25 kg a.i. ha -1 . A weedy check was maintained as control. Cotton variety F.H. 1000 was sown on a well-prepared seedbed in 75 cm spaced rows with hand drill on May 27, 2003. Nitrogen and phosphorous was applied @ 110 and 60 kg, ha -1 , respectively in the form of urea and diammonim phosphate (DAP) as a basal dose. Thinning was done manually when the plants attained 20-25 cm height to maintain 30 cm plant-to-plant distance. Insect pests were controlled by using recommended insecticides. Sorgaab was prepared by following the method devised by Cheema and Khaliq (2000). Volume of the spray was 350 L ha -1 and was sprayed in respective plots by using knapsack hand sprayer fitted with T jet nozzle. The data regarding weed density