RESEARCH NEWS
Fungus that causes dollar spot By J.M. Vargas Jr. Professor, Dept. of Plant, Soil, and Microbial sciences Michigan State University
Introduction
T
he name of the fungus that causes dollar spot has been changed to Clarireedia jacksonii from Sclerotinia homoeocarpa. There are three other species that are responsible for dollar spot throughout the world: Clarireedia monteithiana, Clarireedia homoeocarpa, and Clarireedia bennettii. However, Clarireedia jacksonii is responsible for most of the dollar spot on cool season grasses throughout the world including Michigan.
Folk Lore I like to say turfgrass science has a lot of what I call “folk lore” still in it. This describes beliefs we have about turfgrass management that are based on observations, greenhouse experiments, and things that seem to make sense but do not have replicated research under field conditions to back up these claims. Some of this is because turfgrass science is relatively new compared to research done on field or fruit crops which has been going on for over a hundred years so they have eliminated most if not all of the folk lore. Most of the critical turfgrass research began in the 1960’s but it didn’t really become wide spread at many university until the 1980’s. Maybe the all-time classic folk lore was that Poa annua died in the heat. Of course we now know based on
field research that it dies in the warm weather from disease and insect problems.
Dollar Spot Irrigation Dollar spot has some folk lore associated with it some of which I am personally guilty of. In the three additions of my text book “Management of Turfgrass Diseases” I tell you the worst time to water the turf is in the early evening because the turf will remain wet for a longer period of time thus resulting in more disease. So at Michigan State University we set up an experiment where one set of plots received a .10 inch daily irrigation at either 10 pm or at 5 am for a total of .7 inch a week. A third set of plots received the same amount of irrigation .7 inches a week applied twice a week which represented a deep infrequent irrigation program. The results showed a pm daily irrigation had the least dollar spot followed by the daily 5 am daily treatment with the deep infrequent program having the most dollar spot. We believe the reason the daily irrigation programs had the least dollar spot was because of the moist soils supporting higher levels of bacteria which were antagonistic to the dollar spot fungus. We know moist soils can support high populations of bacteria and that bacterial populations are lower in drier soils. Also included in the study were 3 creeping bentgrass cultivars: L-93 a susceptible cultivar, Declaration a moderately
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MTF NEWS NOTES
| FALL 2021
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