Seasonal growth and shading potential of sugarcane (Saccharum spp. hybrids) and shade response of perennial weeds

Seasonal growth characteristics and shading ability of six sugarcane varieties were compared during the second production year. For each variety, trend analysis of data showed a significant linear trend. Differences in shoot emergence among the varieties were observed beginning in early April and as the season progressed, shoot production and shoot height increased for ‘L 97-128’, ‘Ho 95-988’, ‘L 99-226’, and ‘L 99-233’ but lagged for ‘HoCP 96-540’ and ‘LCP 85-384’. Beginning in mid-April ground cover increased most rapidly for L 99-233. In late May ground cover was around 60% for LCP 85-384 and HoCP 96-540; around 70% for L 97-128, Ho 95-988, and L 99-233; and was approaching 90% for L 99-226. Sugarcane canopy height across the growing season was consistently greater for L 97-128 and L 99-233 and averaged 21% more than for the other varieties in early June and 15% more in mid-July. Based on photosynthetically active radiation (PAR) data collected in the row middles, sunlight in the sugarcane canopy at ground level was reduced an average of 61% in early June for L 97-128 and L 99-226 compared with 29% for LCP 85-384 and HoCP 96-540. By late July PAR reduction was equal and averaged 90% for L 97-128, Ho 95-988, L 99-226 and L 99-233 compared with 78% for LCP 85-384 and HoCP 96-540. Shade studies were conducted in fields with natural infestations of bermudagrass and johnsongrass using enclosures (0.61 x 0.61 x 0.61m) covered with shade cloth providing 30, 50, 70 and 90% shade. At 55 days, bermudagrass ground cover under full sunlight was 88% compared with 10% for 90% shade; above ground biomass for 90% shade was reduced 95%. Exposure to 90% shade for 35 days decreased johnsongrass plant population 86% and above ground biomass 90%. With 30% shade, dry weight of bermudagrass was reduced 30% and johnsongrass biomass was reduced 45%. Based on this research the varieties L 97-128, L 99-226, and L 99-233 should be competitive with bermudagrass and johnsongrass. In contrast, the open canopy of HoCP 96-540 would be conducive to weed reinfestation