Shasta Daisies and Goldenrod Aren't Causing Your Customers' Allergies
Posted: September 20, 2011
The following article ran in Rutgers Cooperative Extension Plant Pest Advisory, Landscape, Nursery and Turf edition, April 21, 2011. It was written by Clare Liptak, retired Somerset County Agricultural Agent, and IPM scout, and reprinted with her permission.
A recent commercial for Claritin showed a woman surrounded by daisies and ornamental goldenrod. Compared to trees, grasses and weeds, members of the daisy family such as sunflowers and goldenrod aren't significant causes of hayfever. So much for truth in advertising.
The real culprits that cause allergies aren't colorful at all. They have tiny, decidedly non-showy flowers shedding pollen dispersed by the wind. These plants don't have colorful petals, or any petals at all; extraneous flower parts would just interfere with dispersal.
Still, some of the most frustrating discussions I've had with allergy sufferers is based on their certainty that spring bloomers or goldenrod are causing their misery. But the general rule is: if it has pretty petals, insects carry the pollen. Plants have showy petals not to please us -- Duh!- - but to attract pollinators. It's too heavy to be carried by the wind and,
therefore, can't be the cause of seasonal allergies.
Dispersal of tree pollen starts in mid-March, peaks around late April, and is generally over by late July. The most important producers of allergenic pollen are alder, birch, ash, hickory, walnut, cedar (Juniperus spp.), sycamore and plane tree, poplar, oak, and elm.
Grass pollen is dispersed from mid-May until mid-September, peaking in mid-June. One of the most prolific pollen producers is sweet vernal grass (Anthoxanthum odoratum). Annual bluegrass blooms next but produces little pollen. Timothy and orchard grass, both important pasture grasses, cause allergies in early summer. That late summer bloomer, crabgrass, doesn't produce enough pollen to be a significant cause of allergies even though it seems like it's everywhere.
Finally the period for weed pollen stretches from Mid-May until early November peaking in late August. Among the main pollen producers is plantain, a perennial, and the giant and common ragweed, both annuals. The 2 ragweeds account for more seasonal allergies than all other pollen sources combined.
For a plant to be an allergen, it has to have three characteristics: buoyancy, abundance, and allergenicity. For example, cattails are common enough in our area and produce lots of wind-borne pollen, but it's not toxic and, therefore, not a cause of allergies. Most conifers also produce buoyant pollen, (in fact, sometimes pine pollen covers my silver car in a yellow haze), but only the junipers, including eastern red cedar are allergenic.
For more information, see the fascinating book Hayfever Plants, by Roger P. Wodehouse, Ph.D. out of print, but available from UMI Books on Demand.