Comparing Iron Sulfate Versus Chelated Iron for Suppression of Microdochium Patch

Previous research focusing on using iron sulfate to suppress Microdochium patch on annual bluegrass putting greens has yielded positive results although often turfgrass thinning or blackening of the turfgrass sward is not considered acceptable.

Clint Mattox, Alec Kowalewski, Brian McDonald, Emily Braithwaite, and Alyssa Cain
Oregon State University

Field trials have shown that applying high rates of iron sulfate in larger carrier volumes or lower rates of iron sulfate in combination with phosphorous acid suppress Microdochium patch while minimizing detrimental effects to the turfgrass.  In spite of this previous research, the iron sulfate rates necessary to control Microdochium patch still result in turfgrass thinning.

Laboratory trials have suggested that chelated iron suppresses the growth of Microdochium nivale, the pathogen responsible for Microdochium patch. It is speculated that chelated iron may suppress Microdochium patch while not adversely affecting turfgrass quality. Therefore, a field trial was initiated in September 2018 to compare iron applied every two weeks as either iron sulfate or as chelated iron (DTPA) in combination or in absence of phosphorous acid. In order to mimic real-world conditions when the applications are made, replicated golfer traffic is being applied to the plots by walking over the area with golf course shoes during the fall and the winter months.

Treatments include:
1) 0.5 # FeSO4 / M 
2) 0.5 # FeSO4 / M + 3.2 oz. Duraphite 12 / M
3) 1.0 # FeSO4 / M
4) 1.0 # FeSO4 / M + 3.2 oz. Duraphite 12 / M
5) 0.1 # Fe as chelated iron / M (equivalent to Fe level in 0.5 # FeSO4)
6) 0.1 # Fe as chelated iron / M + 3.2 oz. Duraphite 12 / M
7) 0.2 # Fe as chelated iron / M (equivalent to Fe level in 1.0 # FeSO4)
8) 0.2 # Fe as chelated iron / M + 3.2 oz. Duraphite 12 / M
9) Fungicide Control
10) Non-treated Control

Preliminary results suggest both iron sources when combined with phosphorous acid produce very little visual differences in disease suppression.  Although, there is some visual evidence that iron sulfate alone may suppress Microdochium patch more than DTPA iron. Visual turfgrass density appears to be higher in plots receiving DTPA iron compared to plots receiving iron sulfate (Image 1).   

Soil testing, digital image analysis, and NDVI data analysis will take place at the conclusion of the first trial year (30th of April 2019).

Image 1: Effects of iron sulfate (FeSO4) or chelated iron (DTPA) in the presence or absence of phosphorous acid (H3PO3) compared to a not treated control and a fungicide rotation on an annual bluegrass putting in Corvallis, OR. For year one of the study, applications began on the 4th of September 2018 and will be applied every two weeks until the 15th of April 19.