FIELD-EVALUATION OF A COMMERCIAL FORMULATION OF THE SPODOPTERA-EXIGUA(LEPIDOPTERA, NOCTUIDAE) NUCLEAR POLYHEDROSIS-VIRUS FOR CONTROL OF BEET ARMYWORM ON VEGETABLE CROPS IN THAILAND

Small-scale field trials were conducted in the Kanchanaburi and Ratcha buri provinces of Thailand between December 1994 and March 1996 to gat her efficacy data to support a registration dossier for a commercial f ormulation of a nuclear polyhedrois virus of beet armyworm, Spodoptera exigua, under the tradename Spod-X. A liquid concentrate formulation of Spod-X was compared with two commercial standards, Bacillus thuring iensis subsp. aizawai (Cen Turi 3.5 WDG) and the insect growth regulat or tebufenozide (Mimic 20F, a benzoylhydrazine ecdysone agonist), for control of beet armyworm on gar den pea, Chinese kale, shallot and tab le grape. Spod-X applied at 4-day intervals at 3.1-12.5 x 10(11) occlu sion bodies (OBs) ha(-1) in a splay volume of 625-1000 l ha(-1) provid ed excellent control of beet armyworm on garden pea and grape (75-100% reductions) after rite second application. On Chinese kale and shallo t, rates of Spod-X in the rate 5-60 x 10(11) OBs ha(-1) sprayed every 4 days in a spray volume of 1000 l ha(-1) provided significant protect ion fi om infestation of beet armyworm over the gr owing season; howev er, efficacy was poor to moderate. Tank-mixing Spod-X with the pyrethr oid, deltamethrin (Decis 3EC), did not improve efficacy on shallot; ho wever, combinations of viis and B. thuringiensis ol tebufenozide achie ved commercially acceptable levels of crop protection on Chinese kale compared with virus alone. Lower levels of control and clop protection observed with all materials on Chinese kale and shallot reflect, in p art, the tendency of S. exigua larvae to feed within sheltered sites a nd directly damage marketable plant parts. In general, all rates of Sp od-X performed as well as, or better than, the B. thuringiensis standa rd (56.3-105 g ha(-1) a.i.) on all crops tested. In general, reduction s of beet armyworm larval populations and plant damage provided by all labeled rates of the chemical standard tebufenozide (125-250 g ha(-1) a.i.), were marginally greater than all rates of Spod-X tested. On cr ops such as pea and grape, where beet armyworm predominately feed on e xposed leaf surfaces, our data unequivocally support the use of Spod-X for cost-effective, season-long pest management. Strategies to improv e the efficacy of virus on shallot and kale ale discussed.