Effects of Chlorsulfuron Herbicide and Sorghum Intercropping with Cowpea on Striga hermonthica Emergence and Sorghum Growth

Abstract

Green house and laboratory experiments were conducted, during the season 2014/2015, at the College of Agricultural Studies (CAS), Sudan University of Science and Technology (SUST) at Shambat, Khartoum North during season 2014. The green house experiment was undertaken to determine the effects of the herbicide chlorsulfuron and intercropping sorghum (cv. Wad-Ahmed) with cowpea (T100K-901-6 cv.) on S. hermontica incidence and sorghum growth. Treatments were arranged in a Randomized Complete Block Design (RCBD) with four replicates. The laboratory experiment was undertaken to study the effects of the herbicide chlorsulfuron on S. hermonthica seed germination. The results of green house showed that Striga emergence increased with increasing size of the seed bank. At 30 DAS, intercropping sorghum with cowpea did not reduced Striga emergence. However, at 45 DAS, intercropping sorghum with cowpea reduced Striga emergence by 16.3%, albeit not significantly. At 30 and 45 DAS, sorghum treated with chlorsulfuron at 3.1 g a.i ha-1, irrespective of Striga seed bank size suppressed the Striga emergence by 96.6 – 100 and 49.0 – 63.6%, respectively. Intercropping sorghum with cowpea and a subsequent treatment with chlorsulfuron reduced Striga emergence (33–37%), but not significantly. Sorghum intercropping with cowpea, irrespective of Striga seed bank size, decreased Striga dry weight by 44.3-50.5%. Chlorsulfuron alone, reduced Striga dry weight by 10-44.3%, but not significantly. Intercropping sorghum with cowpea and a subsequent treatment with chlorsulfuron, decreased Striga dry weight by 22.8 – 70.7%. At 45 DAS, Striga at seed bank size of 16 mg/pot reduced sorghum height significantly (37.8%). At 60 and 75 DAS, S. hermonthica irrespective of seed bank size reduced sorghum height and stem diameter. At 60 DAS, S. hermonthica reduced chlorophyll content and the observed reductions increased progressively with increasing Striga seed bank size. Striga at seed bank size of 8 and 16 mg/pot, reduced significantly sorghum dry weight by 64.8 and 53.5%, respectively. At Striga seed bank of 16 mg/pot, cowpea intercropped sorghum exhibited significant reduction in sorghum height. 60 DAS, Striga at seed bank size of 4 and 8 mg/pot reduced the chlorophyll content in sorghum intercropped with cowpea significantly by 27.4 - 28.5 %. At 60 and 75 DAS, irrespective of Striga seed bank size, cowpea intercropped with sorghum X displayed significant reductions in stem diameter (19.0-56.7%).Sorghum intercropped with cowpea at Striga seed bank size of 16 mg/pot resulted in significant reduction in sorghum dry weight (61.6%). At 30 and 45 DAS, chlorsulfuron treated sole sorghum, displayed a significant reduction in sorghum height. However, at 60 and 75 DAS displayed a significant reduction in sorghum height only at the highest Striga seed bank size (16 mg/pot). At 60 DAS, Striga at a seed bank size of 16 mg/pot reduced chlorophyll content in chlorsulfuron treated sole sorghum by (24.7%). Chlorsulfuron applied to Sole sorghum at Striga seed bank size of 16 mg/pot reduced sorghum dry weight by 51.9%. Sorghum intercropped with cowpea and subsequently treated with chlorsulfuron at Striga seed bank size of 16 mg/pot decreased sorghum height significantly (20.8 – 29.5%). 60 DAS, Striga at seed bank size of 8 mg/pot, decreased chlorophyll content significantly in sorghum intercropped with cowpea and treated with chlorsulfuron. 60 and 75 DAS, sorghum intercropped with cowpea and subsequently treated with chlorsulfuron displayed significant reductions in stem diameter (28-33.3%). Sorghum intercropped with cowpea and subsequently treated with chlorsulfuron, irrespective of Striga seed bank size, reduced sorghum dry weight (28.1- 47.6%).The results of laboratory experiment showed that Striga seeds conditioned in water and subsequently treated with GR24 at 0.01 and 0.1 ppm displayed 65.2 and 76.8% germination, respectively. Chlorsulfuron applied during conditioning reduced Striga seed germination significantly in response to subsequent treatments with GR24.