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Grains and field crops


I.General comments and highlights. 1. Chemical control of powdery mildew gave yield responses of up to 950kg/ha. The size of the response varied both with rate of nitrogen applied and time of planting. It appears that there is a strong interaction between the yield loss due to powdery mildew and nitrogen supply. 2. The earliest time of planting (May 30th) produced significant yield increases over the traditional (June/July) plantings. However the variety used (Stirling) did not extend its vegetative phase with earlier plantings, with the result that the yield response came from an increase in the number of heads per m2 rather than grains per head. 3. The application of potassium fertilizer significantly reduced the level of disease (powdery mildew) on both Stirling and Forrest barley. Nitrogen had no effect on disease level. Waterlogging prevented the collecting of any meaningful yield differences. 4. Seed dressings, Erex and PP450, gave suppression of powdery mildew for around 100 days after planting. Neither chemical had an effect on seedling emergence. Powdery mildew did not develop to significant proportions until late in the season and so yield gains from disease control were minimal. 5. For other trial work on barley powdery mildew, see experimental summary of T.N. Khan. II. Time of planting x N x Powdery Mildew – 84ES40. Ill. N x K x Powdery Mildew – 84ES31, 84E21. IV. Powdery Mildew - seed dressing evaluation – 84ES42.

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Western Australia