Mowing your lawn this weekend? Be aware of the allergenic fungal spores lurking in the grass and soil

Alternaria alternata

Ever wonder why mowing the lawn can bring on hay fever or asthma symptoms? Many people think it must be the grass pollen that is stirred up by the mower. But when you think about it this is highly unlikely given the short stature of lawn grass and, in even moderately maintained lawns, the grasses rarely are able to flower and release pollen before the next mow. The likely culprit causing heightened irritation and allergic responses around lawns, and particularly during mowing, are the microscopic fungal spores known as Alternaria.

The mold Alternaria is a well-recognized allergy causing fungus.  The mold can be found on leaves and stems of plants (including grass) and within soils. Mowing lawns in urban environments and harvesting crops in rural environments can contribute to increasing the abundance of spores in the air. Alternaria spores can be detected from spring through late Autumn in most temperate areas, and can reach levels of thousands of spores per cubic meter of air, particularly during dry, windy conditions, following a period of rain. 

These weather conditions sound familiar? The last two weeks of relatively high rainfall in Canberra, followed by an impending heat wave, has created the ideal conditions for Alternaria to spore and on the 18th November, 2015, we recorded our first EXTREME level of Alternaria alternata in Canberra Daily Pollen count (175 Alternaria alternata particles/m3). These same weather conditions are likely to bring out a lot of home owners wanting to mow their lawn as soon as the fine weather returns. The act of mowing your lawn disturbs a primary site for Alternaria, and in the process may fan large numbers of spores into the air. 

So be aware and take precautions if you are sensitive to Alternaria as there are likely to be very high levels of spores in Canberra’s air over the next few days and especially this weekend.

Clockwise images: Alternaria alternata spore chains; Leaves and stems infected by the mold Alternaria; "dust" created when mowing lawns.