The Carrot Weevil IT IS STILL AROUND BY JUAN R. ANCISO
Adult Carrot Weevil
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carrot weevil, Listronotus texanus (Stockton), has been the key pest affecting carrot, parsley, root parsley, dill and fennel production in South Texas for the past seventy years. The feeding damage by the larvae can kill the young plants of these crops but really this stage makes the insect difficult to control since it is protected from foliar insecticides. While this insect can be quite devastating to these five crops, it is processing carrots that can have the most economic impact by this insect. The presence of larvae and feeding damage in the root are of major concern to carrot processors because of stringent FDA quality control of insect parts in processed food that can lead to loads of carrots being rejected. In addition to loads being rejected, yields can be greatly reduced in processing carrots as well as fresh market carrots, parsley, root parsley, dill and fennel. The cream-white larvae which are legless and relatively slow-moving have proven to be very 6
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difficult to control with insecticide sprays in the crown area and not controllable once in the roots. Once these larvae become pupae in the soil it is impossible to attain any level of chemical control. The adult stage is targeted for chemical control and this chemical application is based primarily on sampling for eggs as an action threshold as an indication that adult carrot weevils have moved into the field. The eggs are difficult to sample due to their pinhead size (1mm long by 0.5 mm wide) and color but still possible for a well trained scout. The coloration and behavior of adults makes them impractical for monitoring either by traps or visual inspection. Management programs from 1961 to 1989 were dependent on six insecticide applications on a calendar schedule specified in producer contracts. During the 1980’s the product often specified in producer contracts was Pydrin (fenvalerate). An iso-
