Wheat Update as of May 15, 2007

Almost all fields are beyond herbicide application. Fields in Essex/Lambton are at the flag leaf emerging stage (Zadok's 37); advanced fields are entering boot stage (Zadok's 41). Boot stage is the last opportunity for strobilurin fungicide applications. In Huron/Bruce, advanced fields are at the flag leaf emerging stage while most fields are between first and second node (Zadok's 31/32). Manganese deficiency is showing up on sandy soils and muck fields. Physiological fleck (1-2mm chlorotic lesions) is common in many fields due to UV light injury. New growth does not show continued flecking. There is no significant disease pressure at this time but things could change with cool, wet weather. Corn row syndrome is evident in some fields.

Bird Cherry Oat aphids continue to be found. Aphid populations above threshold (15 aphids/stem) have been found in one isolated case in south Lambton county. Anyone finding aphid populations past threshold and who would be willing to take part in a field trial is encouraged to contact Peter Johnson (519-318-7769). There is virtually no Ontario data on aphid control at this stage of growth.

Concern exists over fields with herbicides applied the weekend of May 12/13, as low night temperatures (below 2C) may increase phytotoxicity in the crop. When temperatures drop too low, metabolism of the herbicide by the crop ceases. Hormone or phenoxy herbicides then interfere with head development, causing malformed heads and sterility. These symptoms do not become evident until after the head emerges. However, as emerged corn does not show frost injury symptoms from these temperatures, it is hoped that the wheat crop will not be affected in this way.

Weeds as Observed in Essex/Lambton and Huron/Bruce
as of May 15, 2007

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