Silverleaf nightshade (SLN) and prairie ground cherry (PGC) are typical examples of intractable, deep-rooted, summer perennial weeds which significantly impact on livestock productivity and health. McLaren et al. (2004) estimated that average total farm impact of SLN was $1730 per year in direct control costs and $7786 in lost production. Few options other than high rate of expensive residual herbicides, that affect the establishment of following pastures and crops, were available to reduce their spread and impact. This project considerably broadened herbicide control options and identified potential new non-chemical tactics. Current research has demonstrated the importance of controlling perennial weeds through management practices that target both the seedbank and the rootbank. An effective dual spray program for controlling SLN and PGC was developed, with an early herbicide application to early flowering plants in late Spring/early summer to target seedbank, followed by a late herbicide application in late March/early April to target rootbank. This dual spray program can effectively reduce stem emergence by up to 97% in the following year.
Competitive pastures and winter cover crops also provided effective weed suppression, inhibiting the growth of SLN and PGC by 84 - 97%. Research on Eucalyptus allelopathy has demonstrated its potent bioactivity on SLN, providing the basis for the development of a new bioherbicide. Limited host specificity testing of the chrysomelid beetle has indicated opportunity for biocontrol of PGC.
A best management package based on the above chemical and non-chemical options has been developed. This BMP can potentially generate $30/ha profit to growers by cost-effective integrated weed management. Continued research and extension is required to delivery the BMP to growers to reduce weed management costs, improve perennial pasture productivity, and increase capacity of growers to manage perennial weeds.