Oregon State University Update on Fungicide Alternatives for the Control of Microdochium Patch
Since 2013, twelve field trials have taken place focusing on managing Microdochium patch on annual bluegrass putting greens in the absence of fungicides. Trials have included the use of nitrogen, phosphite, iron sulfate, sulfur, horticulture oils, biological control products, and cultural practices.
Based on data collected from 2013-2015, there was a strong suggestion that urea applied at 0.1 #N/M every two weeks does not increase the incidence of Microdochium patch on annual bluegrass putting greens, while 0.2 #N/M does lead to more disease. There was also suggestion that 2.0#FeSO4/M applied every two weeks will suppress Microdochium patch, although this rate of iron sulfate will also lead to abiotic damage. The second phase of research concluded in April 2017 with an additional two field trials considering the differences in spray carrier volumes and timing frequency of 2.0#FeSO4/M. This research suggests that spray applications every two weeks were the most effective as suppressing Microdochium patch and that higher spray carrier volumes (7.5 or 10.0 gal/M) still lead to abiotic damage although the turfgrass color is not darkened as much as with lower carrier volumes (2.5 or 5.0 gal/M).
Other trials taking place from 2013-2015 strongly suggested that Civitas One, sulfur, phosphite, or rolling applied alone or in any combination would suppress Microdochium patch, although treatments including rolling in combination with Civitas One would lead to abiotic damage. Since 2015, five more trials have taken place to explore methods of managing Microdochium patch without the adverse effects of abiotic damage. The data from these subsequent trials suggest that combinations of 0.25# S/M and phosphite (applied at 0.075# H3PO3/M) applied every two weeks suppress the incidence of Microdochium patch better than sulfur or phosphite applied at the same rates alone.
Among all the trials to date, the most promising results have been observed when treatments of 8.5 oz. Civitas One/M were applied every four weeks in combination with 0.075# H3PO3 (phosphite)/M in rotation with a combination of 0.5# S/M and 0.075# H3PO3/M. Under traffic replication (76 rounds of golf a day), this treatment combination provided suppression of Microdochium patch comparable to a traditional fungicide and no abiotic damage was observed.
Two more field trials are taking place this winter. One is exploring rates of Civitas One and phosphite at different timings as well as the effects of using Civitas One for only certain months of the winter. The second trial is exploring the use of phosphite in combination with iron sulfate to elucidate if the addition of phosphite may reduce overall iron sulfate use and lead to less abiotic damage.
Clint Mattox, Alec Kowalewski, & Brian McDonald
Photos taken on 02-18-2017. Starting on Sept. 22nd 2016, left plot (upper image) received 8.5 oz. Civitas One/M in combination with 0.075# H3PO3 (phosphite)/M in a four-week rotation of a combination of 0.5# S/M and 0.075# H3PO3 /M. The plot on the right (lower image) was not treated.