c06-09-0565(5) Horvath.indd

Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) causes one of the most important diseases faced by golf course superintendents throughout the USA. Fungicides are effective, but fungicide resistance and regulation have restricted their use. Site-specifi c application allows more judicious use of fungicides, but the spatial heterogeneity of dollar spot incidence has been unknown. An intensive study was designed to determine the spatial distribution of dollar spot incidence using geostatistical analysis. Dollar spot foci were manually counted every 2 to 3 d in 200 quadrats in 2000, and in 888 quadrats in 2001 and 2002. Variograms showed spatial aggregation of dollar spot foci on a small scale, and remained stable throughout the growing season despite increasing disease incidence. The range parameter of the variograms was stable within a season, with values ranging between 2.5 and 9.5, 1.3 and 1.9, and 1.2 and 2.2 m in 2000, 2001, and 2002, respectively. Kriged maps of dollar spot incidence also show a stable pattern of spatial aggregation remains throughout the growing season. The locations of dollar spot clusters changed between seasons, but the variograms from each season were similar, further suggesting stability of the spatial structure. It appears that limited secondary dispersal of S. homoeocarpa occurs during epidemics, as evidenced by the stable variograms observed throughout the three growing seasons. The underlying factors involved in the observed stability are unknown. B.J. Horvath, Dep. of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061; J.M. Vargas, Jr., Dep. of Plant Pathology, Michigan State Univ., East Lansing, MI 48824; A.N. Kravchenko and G.P. Robertson, Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824. This work was supported by a Project GREEEN grant (GR00-037) from the Mich. Agric. Exp. Stn., East Lansing. Received 5 Sept. 2006. *Corresponding author ([email protected]). Abbreviations: PSV, proportion of structural variance; VCG, vegetative compatibility groups. Published in Crop Sci. 47:1206–1216 (2007). doi: 10.2135/cropsci2006.09.0565 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Published online May 31, 2007