Management of thrips (Thrips tabaci Lindeman) on organically raised rose onion

Rose onion (Allium cepa L.) is a special type of onion more pungent than normal onions and cultivated in parts of south India exclusively for export to Malaysia, Singapore, Indonesia, Bangladesh and Sri Lanka. Only medium sized (25 to 35 mm diameter) bulbs are preferred for export. Onion thrips, Thrips tabaci (Lindeman), a regular pest of onions, is often a serious pest on rose onions too. At present, rose onion is grown exclusively under inorganic condition with fertilizer and insecticide regimes. Bulbs that are organically grown are free of pesticide residue, contribute to value addition and fetch premium price in international market. Studies were carried out at the Indian Institute of Horticultural Research, Bangalore from December to April 2004–05 and 2005–06 to compare the management of thrips on rose onion under organic and inorganic cultivation. Organic and inorganic plots received a basal dose of NPK (as farm yard manure or inorganic fertilizers). Further, neem seed kernel extract 4% for organic plots and acephate 75 SP @ 0.1125% (1.5g/liter) for inorganic plots were sprayed at 15 days interval from the first appearance of thrips. Results indicated that incidence of thrips and total yield was on par in both inorganic and organically raised rose onion. However, bulbs when graded into small <25 mm), medium (25–35 mm) and large (>35 mm), significantly higher yield of medium sized (11.33 tonnes/ha) export quality bulbs was recorded in organic cultivation compared to inorganic cultivation (3.68 tonnes/ha). Further, higher number of large and split bulbs were recorded in inorganically raised rose onions. Total soluble solids (TSS) content was higher in organically raised bulbs. Bulbs resulting from organic cultivation were lustrous. The importance of the study on organic farming and export of rose onion is discussed.