Inter-seasonal population dynamics and cultural management of Helicoverpa spp. in a Central Queensland cropping system

Abstract

A strategic trap cropping program targeting Helicoverpa spp. on cotton was developed and implemented in the Emerald irrigation area of Central Queensland beginning in the winter of 1997. Growers were advised to plant 1% of total cropping area to a trap crop of chickpea (Cicer arietinum) in winter and pigeon pea (Cajanus cajan) in summer. The population dynamics of Helicoverpa spp. in relation to the Emerald cropping system was studied over a 3-year period (August 1996–July 1999) to provide a framework for testing the validity of key assumptions underlying the trap cropping strategy and optimising the implementation of the program. The population dynamics study showed continuous production of Helicoverpa pupae (moths) in the crop production system during each calendar year. The pattern of pupae production was consistent with cycling of Helicoverpa populations between irrigation and rainfed cropping components of the system. Spring rainfall and the availability of host plant resources is shown to impact on the population dynamics of Helicoverpa in the cropping system and its pest status on early-season cotton. Performance and potential impact of the trap crops are discussed within the context of host plant availability and resource bottlenecks. It is shown that the impact of the trap crops on abundance of Helicoverpa spp. early in the growing season could not be distinguished from that of naturally occurring host plant resource bottlenecks in spring most likely as a result of suboptimal timing of trap crop destruction. The potential contribution of cultural control tactics to integrated pest management of Helicoverpa spp. in cropping systems is discussed.