The impact of fungicide and herbicide timing on foliar disease severity, and barley productivity and quality.

Turkington, T.K., O'Donovan, J.T., Harker, K.N., Xi, K., Blackshaw, R.E., Johnson, E.N., Peng, G., Kutcher, H.R., May, W.E., Lafond, G.P., Mohr, R.M., Irvine, R.B., and Stevenson, C. (2015). "The impact of fungicide and herbicide timing on foliar disease severity, and barley productivity and quality.", Canadian Journal of Plant Science, 95(3), pp. 525-537. doi : 10.4141/CJPS-2014-364  Access to full text

Abstract

There is interest in mixing herbicides with a half-rate of fungicide at herbicide timings for barley in western Canada. At six sites across the Canadian prairies from 2010 to 2012 combinations of herbicide and the fungicide Tilt® (propiconazole) were applied to barley at the two- to three-leaf stage (herbicide and half-rate fungicide), five- to six-leaf stage (herbicide and half-rate fungicide), and/or the flag leaf stage (full or half-rate fungicide only). Each plot area was cross-seeded with tame oat as a model weed prior to seeding. Upper canopy leaf samples were collected for leaf disease assessment at the early dough growth stage. Weed biomass, and grain yield and quality were determined. Total leaf area diseased (a combination of scald, both forms of net blotch and spot blotch) was greater for the two- to three- or five- to six-leaf stage herbicide-only treatments and the combination herbicide and half-rate fungicide treatments compared with fungicide at the flag leaf stage. Yield, 1000-kernel weight, kernel plumpness and test weight were greatest and kernel thins lowest for treatments with a flag leaf stage fungicide application. Split applications of fungicide at the time of herbicide application and at flag leaf emergence did not improve disease management and crop productivity compared with a single full rate fungicide application at the flag leaf stage. Weed biomass was generally not influenced by the treatments because weed control was excellent at all sites. However, yield was lower when herbicide was applied at the five- to six-leaf versus the two- to three-leaf stage. For improved leaf disease management and yield in barley, fungicide applications should include a flag leaf stage timing for adequate protection of upper canopy leaves, which are key contributors to yield and grain filling. Delaying herbicide application to the five- to six-leaf stage in an attempt to accommodate a fungicide application reduces barley yield due to early-season weed interference.

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