RADIOMETRY ACCURATELY MEASURES CHLORSULFURON INJURY TO BARLEY

Chlorsulfuron was applied post-emergence to four barley (Hordeum vulgare L.) cultivars sown at the end of May (sowing date 1, SD1) and mid June (SD2) in weed-free field trials at Wagga Wagga in 1990. Crop growth and development was measured from the time of application to maturity by destructive harvests and using a multispectral radiometer. Chlorsulfuron significantly (P < 0.05) reduced dry matter (DM), leaf area index (LAI) and tillering as measured by destructive harvests between the three-leaf stage and anthesis, from both SD1 and SD2, and there was no significant (P > 0.05) interaction between cultivar and herbicide treatment. The interaction between cultivar and chlorsulfuron was marginally significant (P < 0.1) for LAI as measured by the radiometer (LAI-R) from SD2. Tolerant cultivars (Grimmett and Lara) had greater LAI-R than the sensitive cultivars (Schooner and Clipper) in all treatments at all stages of development. LAI-R of the untreated controls reached a plateau at the end of tillering, whereas LAI-R of chlorsulfuron-treated barley increased until mid-jointing. LAI-R of sensitive cultivars showed a greater proportional reduction from chlorsulfuron treatment between the end of tillering and mid-jointing than did the tolerant cultivars. The radiometer showed potential as a rapid, non-destructive and inexpensive method for measuring crop damage caused by herbicides. The effect of chlorsulfuron on grain yield depended significantly on the cultivar (herbicide x cultivar interaction, P < 0.05). At SD1, chlorsulfuron reduced grain yield of Schooner to 54% of untreated controls and Clipper to 66%, compared with the more tolerant Grimmett (83%) and Lara (76%). Similar but smaller responses were measured from SD2. Kernel number per m2 was the most important determinant of yield reflecting the early effect of the herbicide on crop growth.