สำนักราชบัณฑิตยสภา

The Journal of the Royal Institute of Thailand Volume III - 2011 165 Kuakoon Piyachomkwan, Morakot Tanticharoen technology as well as to increase cassava root productivity. The development of cassava-bioethanol production technology aims for a process with high-yield (litre of ethanol per kg of cassava feedstock), energy and water saving, as well as near-zero discharge to ensure that all biomass residues are completely exploited with minimal resource consumption [1]. Yields or root productivity of cassava roots vary significantly with varieties and growing conditions. Higher root yields can be obtained by well-managed farm practices including time of planting (early in the wet season), land preparation (plowing by hand or mechanically and ridging), preparation of planting materials (age of parent plants, storage of stems, length and angle of cuttings, chemical treatment), planting method (position, depth of planting and spacing), fertilization (type of fertilizers-chemical vs. organic, dosage, time and method of fertilizer application), erosion control, weed control, irrigation and intercropping [2, 3]. The most serious pests of cassava include mites, hornworms, whiteflies, mealybugs, lace bugs and stemborers. Mealybug attacks in Thailand resulted in yield losses estimated as high as 25% in 2009/2010 [4]. To minimize the use of chemical pesticides, biological control can be applied for pest management. The fungus Beauveria bassiana is a broad-spectrum insect pest that can be utilized in insect pest control. Although it can infect and kill many insect pests, its efficiency (assessed as a percentage of insect death after inoculation by the fungus) can vary greatly (approx. 20-100%). The fungus B. bassiana has been used to control the destructive mealybugs in cassava fields in Thailand. The field trial results indicated that a spray of B. bassiana spores along with water-drip irrigation could decrease the mealybug population by up to 75% compared with a no-spray, no-irrigation control. This decrease in mealybug population was prominent particularly in the dry season or in a no- or low-rainfall period during the rainy season. The use of this biological control fungus could increase a population of natural enemies of mealybugs such as lacewing, ladybug, or spider in Beauveria -treated plants compared with pesticide-sprayed plants. Better understanding of insect pathogenesis mechanisms by the fungus on insects will be fundamental for improvement of its efficiency in field use. The highest root productivity has been reported in India (i.e. 40 tons/ hectare) for a small plot of planting area which is irrigated rather than rainfed. In Thailand, the national average yield of cassava root is approximately 20-25 tons/ hectare. Instead of relying only on rainfall, irrigation by water dripping is now 160-170_mac9 5/3/12, 11:43 PM 165