Why do wheat and wheat products, and barley and barley products have different duty rates, at different times of the year?

The different duty rates are referred to as the “Within and Over Access” quota. The Within access quota duty rates are available to all importers of wheat and wheat products, and barley and barley products until the allotted quota amount for the year has been used. Once the quota has been filled for the year, the Over Access rates will apply. The yearly Within Access quota rates are available on Aug.1 of each year and is usually filled by the first week or two of October. The exact end date varies each year as the quota is used up. So a notice will be issued by the Department of Global Affairs (Also known as EICS) with the yearly end of quota date.

This means that the lower (within access) duty rates are available from August 1 to sometime early in October. Outside of those dates, the higher (over access) duty rates apply (for the remainder of the year to July 31 of the next year).