Table 2 Timing and concentration of suspect pollens and mould spores in various geographic areas across Canada [6]

British Columbia (Coastal)

• Season: early February to mid-July

• Primarily deciduous trees (alder, birch, poplar, elm, oak)

• Season: end of April/beginning of May to September

• Highest grass concentrations: early June to mid-July

• Not usually a major factor; no native ragweed

• Present throughout the year except for few weeks when ground remains frozen; increase further in September and October

• Most prevalent spores: Cladosporium and basidiomycetes

British Columbia (Interior)

• Season: late March to mid-July

• Primarily deciduous trees (willow, birch, poplar)

• Season starts in early May in southern parts of the province; starts up to 1 month later in northern parts

• Ragweed is minimal

• Cladosporium can occur from April to late fall

Prairie provinces

• Season: first week of April until June

• Primarily deciduous trees (willow, birch, poplar, alder, elm, oak, ash)

• Season: mid-May to end of September (peak is usually mid-June to early July)

• Most common: nettles and sage brush

• Some ragweed, especially in Manitoba

• Can occur through spring, summer and early fall (Alternaria, Cladosporium)

Ontario and Quebec

• Season starts early April in southern Ontario and Quebec; may occur 4–6 weeks later in northern parts

• In southern Ontario, most common are deciduous trees (birch, poplar, oak, maple, ash, elm, mulberry, willow, chestnut, hickory, Box Elder, beech, alder, walnut, sycamore, pine and juniper)

• In northern Ontario, birch and poplar most common

• In Quebec, ash, poplar, birch most common; maple, alder and oak are less prevalent

• Season starts mid-to-late May; a couple of weeks later in northern areas

• Latter part of May and mid-June are peak seasons for grass pollination

• Ragweed season in Southern Ontario and Southwestern Quebec begins early-to-mid August

• Reaches peak in late August/early September

• Stops at first frost (variable)

• Nettle and plantain can also contribute

• Occur during spring, summer and fall months

• Concentrations may be higher late summer to fall months in Quebec

• Alternaria and Cladosporium are the predominant moulds

Maritimes & Newfoundland/Labrador

• Season: late March to last week of June

• Primarily deciduous trees (birch, poplar, alder, maple, oak, and ash)

• Season: mid-May to end of September

• Peaks in early June

• Ragweed: early August to end of September

• Levels higher during the late summer and early fall months

• Alternaria and Cladosporium are the predominant moulds