Effect of Seed Treatments and Fall-Applied Foliar Fungicides On Winter Wheat Stand Establishment and Yield.

There is disagreement in anecdotal reports regarding the influence of seed-applied fungicides, insecticides or combinations of both on winter wheat (Triticum aestivum) crop growth and vigour.  A study was designed and conducted at 8 sites across the Canadian prairies to determine the influence of seed-applied fungicides and insecticides on fall stand establishment and overwinter survival of winter wheat.  We were also interested in the response of winter wheat to foliar-applied fungicides performed in the fall instead of the spring.  The two factor experiment consisted of 5 levels of seed treatment 1) Check – no seed treatment, 2) tebuconozole (‘Raxil 250’), 3) metalxyl (‘Allegiance’), 4) imidacloprid (‘Stress-Shield’), and 5) dual fungicide/insecticidal seed treatment: tebuconozole + metalxyl + imidacloprid (‘RaxilWW’); and 2 levels of fall-applied fungicide 1) Check – no application, or 2) foliar-applied prothioconazole (‘Proline’) performed in mid-October.  Plant stands did not differ, but plant growth and vigour appeared to improve with seed treatments if there was a response.  A combined mixed model analysis of all 8 sites indicates the interaction of seed treatment and fall-applied foliar fungicide strongly affected grain yield.  The dual seed treatment ‘Raxil WW’ improved grain yield over the check (no seed treatment) and metalxyl alone.  A by-site analysis of sites with confirmed stripe rust (yellow rust, caused by the fungus Puccinia striiformis) pressure in the fall (Lethbridge, AB; Melfort and Scott, SK) indicates that applying foliar fungicides in the fall will improve grain yield over no application of foliar fungicides.  In terms of grain yield stability (yield vs. CV of the treatment), the dual seed treatment, with or without fall-applied foliar fungicide, produced high grain yield with optimal stability.  The lowest and most variable treatment was untreated grain that did not receive a fall application of foliar fungicide.  The other seed treatments generally gained stability and some improvement to yield with the addition of the fall-applied foliar fungicide.  The results suggest that dual seed treatments reduce risk in winter wheat production systems and that fall applications of foliar fungicides are warranted when stripe rust symptoms are observed in the fall.