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

From: Allergen-specific immunotherapy

  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 to September
• Highest grass concentrations: early June to mid-July
• Not usually a major factor; no native ragweed • Levels higher in the spring; 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
Prairies • Season starts in the first week of April and continues through June&#8226 Main deciduous trees: birch and poplar; alder, maple, elm, oak, ash, and willow may also contribute • Season starts in mid‐May and continues to the end of September&#8226 Peak season is usually mid‐June to early July • Most common weeds: nettles or sage brush&#8226 Some ragweed, especially in Manitoba) • Can occur through the spring, summer, and early fall&#8226 Alternaria and Cladosporium are the predominant moulds
Ontario and Quebec • Season starts early April in southern Ontario and Quebec; may occur 6 weeks later in northern areas
• In southern Ontario, most common are deciduous trees (birch, poplar, oak, maple, ash, elm, mulberry, willow, chestnut, hickory)
• 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
• 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 • Season in New Brunswick and Nova Scotia: 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