A review on weed management in sugar cane: Critical periods of Paspalum paniculatum and Paspalum urvillei

The adverse effect of weed competition in sugar cane is not experienced before several weeks following weed emergence. Weeds transplanted 10 WAP caused no significant change in cane yield response as compared to those transplanted 4 WAP. Paspalum paniculatum was often found to be more competitive than P. urvillei, although the latter produced more leaf area and grew taller to intercept more light within the canopy. This indicated that other mechanisms of weed interference were involved and competition for light was more important during the earlier (tillering) growth stages. Root competition was shown to be as important as shoot competition. Root competition effects were observed several weeks after imposing competition, suggesting that it was more important than competition for light in the post-tillering phase. The application of root exudates from the two types of grass to sugar cane confirmed an allelopathic effect on the root biomass of sugar cane. One chemical identified in the leachates from both Paspalum species for the allelopathic effects was 2-propenoic acid, 3-(4-methoxyphenyl). The main implications of the above findings for the Indian sugar industry would involve a change in the timing of the application of herbicides. A new tank-mix consisting of trifloxysulfuron + ametryn and amicarbazone has been found to meet this objective. In ratoon cane, CPWC with natural weed infestations started between 228 and 916 growing degree days (GDD), and ended between 648 and 1311 GDD, depending on the site and cane variety. These results represented a maximum CPWC of 12 to 28 weeks after harvest (WAH). In-plant cane, the CPWC started earlier (6WAP) and was longer than those in ratoon cane.