The Importance of Wind Gusts in Distributing Fungal Spores Among Crop Foliage

New measurements show that in a barley crop wind gusts of more than five times the mean speed occur frequently. Moreover, for the impaction of fungal spores to crop foliage, the known dependence of impaction efficiency on wind speed shows that at low speeds the efficiency increases rapidly as wind speed rises. If it is wind gusts that cause spores to be lifted from plant surfaces and to enter the airstream, then calculations show that in a gusting wind the efficiency of impaction to surfaces will be higher than would be predicted from the mean wind speed. These findings are supported by results from field experiments that investigated the lift-off from plant surfaces and from metal plates, respectively, of spores of Erysiphe graminis (barley mildew) and of lycopodium (club moss). This influence of gusts may thus explain in part why, within crops, spore concentration and deposition change rapidly with distance from spore source.