137 Purple Amaranth Larvae of the stem borer Lixus truncatulus Pest The basal part of the plant containing the pupae swells and plant growth is much retarded. Many commercial growers now spray with insecticides regularly, up to twice a week, instead of using the traditional control method of spreading wood ash to dispel insects. In order to avoid harmful residues, the use of less toxic chemicals is strongly recommended. 8,668