Weeds, Pests and Diseases

Abstract

Weeds, innocuous and yet undesirable plants, need to be managed effectively in the widely spaced sugarcane crop. According to Peng (1984), 200 weed species are known to infest sugarcane fields and 30 are of economic importance. The most common families are Cyperaceae (35%), Umbelliferae (30%) and Gramineae (18%). Quoting FAO figures, May (1980) has listed that globally there are 10 noxious weed species and 7 which are difficult to control. These are Cyperus rotundus, Cynodon dactylon, Echinochloa crusgalli (sensitive to dalapon), Sorghum halepense, Imperata cylindrica, Panicum maximum and Eleusine indica. Other weeds of economic importance in sugarcane fields include Ageratum conyzoides, Panicum repens, Tridax procumbens, Portulaca oleracea and Digitaria sp. In Asia and the Pacific region, Ipomoea hederacea has reduced the cane yield by up to 25% by twining around clumps. This results in bending of the cane which reduces the height and girth and interferes with harvest operations. A similar effect of I. hardwichii has been seen in India and Taiwan. The root parasite Aeginetia indica takes food from the sugarcane through its haustorium. This parasite produces enzymes which reduce sucrose to glucose. Peng (1984) observed that healthy plants contain 13.08% sucrose compared with 5.09% in affected plants and he observed that NCO310 is highly resistant to this parasite. Thus, the losses caused by weeds are enormous as they compete for light, moisture and soil nutrients in addition to serving as alternative hosts for many pests, diseases, viruses and mycoplasmas.