Reduced efficacy and enhanced degradation of carbetamide after repeated application in Australia

Following reports of poor weed control, the effectiveness of repeated applications of carbetamide atid propyzamide in controlling Lolium rigidum Gaud, (annual ryegrass) was examined under field conditions. Repeated applications of carbetamide or propyzamide were less effective in controlling L. rigidum than an initial application. A single application of carbetamide or propyzamide was sufficient approximately to halve the efficacy of a subsequent treatment with the satne herbicide. Laboratory incubations of soil linked the poor performance of carbetamide upon repeated application to an enhanced deg-radation rate. We conclude that the repeated application of carbetamide or propyzamide results in less effective weed control under field conditions and that this can be partially avoided by rotation between carhetamide and propyzamide.     

Assessment of defined antigens for the diagnosis of bovine tuberculosis in skin test-reactor cattle

The continued use of purified protein derivative (PPD) tuberculin is considered to be the main factor which limits the specificity of diagnostic tests for bovine tuberculosis (TB). This study evaluated a whole blood interferon-gamma (IFN-gamma) assay and compared the diagnostic potential of PPD with two tuberculosis-specific antigens, ESAT-6 and MPB70. To provide estimates of sensitivity and specificity, responses were measured in 180 skin test-reacting cattle, of which 131 were confirmed as tuberculous, and in 128 cattle from TB-free herds. For the skin test reactors, there was a positive correlation between the IFN-gamma responses to PPD from Mycobacterium bovis (PPDB) and PPD from Mycobacterium avium (PPDA), indicating cross-reactivity between these complex antigens which are the basis of the skin test. In comparisons of the ESAT-6 IFN-gamma test with a PPD IFN-gamma test (using PPDB compared with PPDA), there was a decrease in sensitivity (76.3 per cent vs 89.3 per cent), but a clear increase in specificity (99.2 per cent vs 92.2 per cent). The provision of high specificity, even with lower sensitivity, offers major benefits for testing in areas with a low incidence of TB.