Evaluation of Potassium Phosphite for Control of Microdochium Patch On An Annual Bluegrass Putting Green.



A study was conducted to investigate the effectiveness of biweekly applications of potassium phosphite applied at 0.08 lbs per 1,000 sq. ft. for the control of Microdochium patch (Microdochium nivale) not under snow cover.  Potassium phosphite applied as P-K Plus 3-1-8 with 14% phosphite (Grigg Brothers) was applied in three treatment combinations: alone, with Ultraplex 5-0-3 (Grigg Brothers), and with Iprodione PRO 2SE (BASF) at 6.0, 3.0, and 4.0 fl oz per 1,000 sq. ft., respectively.   Additionally, Iprodione Pro 2SE was applied alone at 4.0 fl oz per 1,000 sq. ft. and a fertilizer check without potassium phosphite was applied as a comparison.  The trial was initiated September 2, 2010 with the last application made on April 4, 2011.  The total nitrogen applied for each biweekly treatment was less than 0.03 lbs per 1,000 sq. ft. per application.  Eight additional applications of soluble fertilizer totaling 2.5 lbs of nitrogen per 1,000 sq. ft. were made throughout the trial.  Plots were rated visually every two weeks for percent disease cover and overall plot quality.  Data were subjected to analysis of variance and means separated using Fisher’s protected LSD (α=0.05). By mid March, the untreated plots averaged nearly 30 percent disease cover, whereas the plots treated with PK Plus applied alone, or with Ultraplex or Iprodione Pro 2SE averaged less than 1 percent disease cover.  The fertilizer check averaged 3 percent disease cover and the plots treated with Iprodione Pro 2SE alone averaged 7 percent disease cover.  By mid April, plots treated with PK Plus averaged 3 percent disease cover which is severe enough to necessitate a fungicide spray at most golf courses in the Pacific Northwest.  The results of this trial indicate that biweekly applications of potassium phosphite and soluble fertilizer throughout the fall, winter, and early spring significantly reduce the severity of Microdochium patch.