Field use of granulosis virus to reduce initial storage infestation of the potato tuber moth, Phthorimaea operculella (Zeller), in North Africa.
Granulosis virus (a Tunisian isolate) was tested in field conditions in Tunisia, both in spray and as an additive to a powder commonly utilized as a carrier for insecticides (magnesium silicate), in an attempt to reduce Phthorimaea operculella damage to potatoes at harvest. Both spray and powder treatments were applied to the surface soil, only incidentally reaching the plants. The progress of infestation during storage was also examined in untreated potatoes imported from fields which had received previous applications of granulosis virus. Field infestation of tubers at harvest was reduced signficantly by use of the spray (73%) or the powder (35%). Infesting populations of the gelechiid failed to develop in stored untreated potatoes from field areas previously treated with the spray or powder compared with potatoes from untreated areas. Field application of granulosis virus in spray form to surface soil is recommended as a method of reducing infestation at harvest in areas with Mediterranean climate conditions. Field application of the spray also has the added benefit of reducing the evolution of P. operculella in stored potatoes.