INTERACTION OF BROWN LEAF SPOT WITH POST -EMERGENT HERBICIDES IN NARROW LEAFED LUPINS

Inoculation with P. setosa conidia , the infected plants had significantly lower dry weight compared to the same spray treatments in the un-inoculated set except metribuzin 225 g/ha (double the label rate) and diflufenican 100 g mixtures with tepraloxydim 60 g + Hasten® 1% or quizalofop 75 g/ha + BS 1000® 0.2 %. Further, application of herbicides to the brown leaf spot infected plants did not increase disease severity (except diflufenican + tepraloxydim + Hasten®), reduce plant height and dry weight compared to disease only treatment. These results indicate that there is no in the routine screenings on tolerance of new lupin varieties to herbicides, the testing is conducted under disease and weed free conditions. Not much information is available on the impact of foliar diseases like brown leaf spot on tolerance of lupins to herbicides. Thus a glasshouse experiment was conducted in 2008 at Northam, Western Australia to investigate the impact of brown leaf spot ( Pleiochaeta setosa ) infection of lupins on the plants’ tolerance to post-emergent herbicides. The results reinforced that application of herbicides at the registered rates to healthy lupin plants (not inoculated with P. setosa conidia ) are not injurious to plant growth. Under moderate to high disease pressure, produced by the negative interaction between brown leaf spot and post-emergent herbicides, at the registered rates, on lupins. Thus application of post-emergent herbicides, according to label recommendations, to the brown leaf spot infected crops can be expected to achieve effective weed control without increased negative impact on growth and development of lupins.