Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2006
Publication Date: 9/30/2006
Citation: Pfender, W.F., Graw, R., Bradley, W., Carney, M., Maxwell, L. 2006. Use of a complex air pollution model to estimate dispersal and deposition of grass stem rust urediniospores at landscape level. Agricultural and Forest Meteorology.139:138-153.
Interpretive Summary: Stem rust is the most damaging disease of cool-season grasses grown for seed. Spores of the stem rust fungus can be carried by the wind, spreading the disease from one field to another. We used field and laboratory measurements, and a complex model originally developed to describe movement of particulate air pollution, to estimate how far spores can travel under typical weather conditions. From a large, heavily infested field, 10,000 spores can be deposited per day in every square meter of ground up to 1.5 km downwind of the field. This number of spores can result in economically significant damage within one additional generation of the stem rust fungus. The number of spores deposited is lower for source fields that are smaller and/or have less disease. Under most weather scenarios typical of the summer growing season, most spores are deposited within an hour of their release. Certain conditions, such as small whirlwinds known as dust devils, lift spores higher in the air and result in a small proportion of the spores remaining airborne high in the atmosphere. Such spores can move for hundreds of km before being washed down by rain.
Technical Abstract: Dispersal and dry deposition of the urediniospores of Puccinia graminis subsp. graminicola from infected perennial ryegrass was modeled with CALPUFF, a Lagrangian puff atmospheric dispersal model developed for air pollution studies. Weather observations at the study site were combined with three-dimensional prognostic meteorological fields generated by the Penn State Meteorological Model (MM5) using CALMET to run CALPUFF. The settling velocities of single and clustered spores were measured in the laboratory. Deposition fields and mass balances were modeled by using observations from four dates in June 2005. A deposition level of 10 spores/m2 was estimated to reach 0.6 to 1.6 km downwind of the plot on different days. The spore emission rates and weather fields from two of the dates were used in CALPUFF simulations of spore dispersal from a 50-ha field of perennial ryegrass with a range of average disease severities. On one date, deposition of 10 spores/ m2 was indicated to reach 2.8 or 4.1 km from a lightly or heavily infested field, respectively, and comparable distances for deposition of 10,000 spores/ m2 were 0.5 and 1.5 km. 4.5 million spores (a millionth of a % of those released above the canopy) remained airborne for several hours, and 90,000 were modeled to remain aloft at least 200 km from the source. On the other date, which had more stable atmospheric conditions, given deposition levels were slightly closer to the source than for the 14 June outcome and no spores remained airborne an hour after their release. Simulation of a dust devil event showed 25% of the spores advected horizontally beyond 200 km in the air aloft.