Refinement of splatter gun technology for control of bellyache bush (Jatropha gossypiifolia)

Abstract

Bellyache bush (Jatropha gossypiifolia L.) is an erect perennial shrub that is toxic to livestock and capable of forming dense infestations in riparian and rangeland areas. It is widespread throughout northern Australia and, as such, has been classified as a Weed of National Significance. Previous work has shown that splatter gun application (i.e. low-volume high concentration) of metsulfuron-methyl can achieve 100% mortality of bellyache bush plants when each plant is treated individually. The focus of this study was to determine whether similar results could be obtained with this technology to control medium to high density infestations using a broadcast approach (i.e. applying a certain amount of herbicide mixture on a surface area basis). The efficacy of metsulfuronmethyl was compared to that of triclopyr/picloram/aminopyralid and aminopyralid/metsulfuron-methyl. Two rates of each herbicide were applied to plots of c.a. 5 m x 5 m size, in which efficacy associated with distance from the spray operator (i.e. spray front) was also assessed by sub-dividing the plots into 1 m strips. Eleven months after treatment (MAT), average plant mortality for metsulfuron-methyl was 93 and 99% for the low and high application rates, respectively. Furthermore, efficacy declined only slightly with increasing distance from the spray operator, with >90% mortality recorded at a distance of 4-5 m. Inclusion of aminopyralid did not enhance the efficacy of metsulfuron-methyl, whilst triclopyr/picloram/aminopyralid was relatively ineffective, achieving no more than 55% mortality at the highest application rate. Metsulfuron-methyl appears to be the best herbicide for treating isolated to dense infestations of bellyache bush using low-volume high concentration applications but follow up control will be needed to treat surviving plants and to control subsequent seedling growth.