Table 2.

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

	Tree pollen	Grass pollen	Weed pollen	Mould spores
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