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 Ratchaburi provinces of Thailand between December 1994 and March 1996 to gather efficacy data to support a registration dossier for a commercial formulation 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 thuringiensis subsp. aizawai (Cen Turi 3.5 WDG) and the insect growth regulator tebufenozide (Mimic 20F, a benzoylhydrazine ecdysone agonist), for control of beet armyworm on gar den pea, Chinese kale, shallot and table grape. Spod-X applied at 4-day intervals at 3.1-12.5 x 10(11) occlusion bodies (OBs) ha(-1) in a splay volume of 625-1000 l ha(-1) provided excellent control of beet armyworm on garden pea and grape (75-100% reductions) after rite second application. On Chinese kale and shallot, 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 protection fi om infestation of beet armyworm over the gr owing season; however, efficacy was poor to moderate. Tank-mixing Spod-X with the pyrethroid, deltamethrin (Decis 3EC), did not improve efficacy on shallot; however, combinations of viis and B. thuringiensis ol tebufenozide achieved 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 part, the tendency of S. exigua larvae to feed within sheltered sites and directly damage marketable plant parts. In general, all rates of Spod-X performed as well as, or better than, the B. thuringiensis standard (56.3-105 g ha(-1) a.i.) on all crops tested. In general, reductions 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 crops such as pea and grape, where beet armyworm predominately feed on exposed leaf surfaces, our data unequivocally support the use of Spod-X for cost-effective, season-long pest management. Strategies to improve the efficacy of virus on shallot and kale ale discussed.