Above normal daytime temperatures of 90+ degrees have been accumulating quickly (now up to 11 days in Lemont, IL), and the combination of high nighttime temps and high dew points has created a precarious situation for the rapid appearance of brown patch. This soilborne fungal disease is caused by the pathogen Rhizoctonia solani. Recent weather has been fairly dry since July 4th, and although it has been much needed for superintendents, it has added further
environmental stress to any previously weakened turfgrass plants. Damage by Rhizoctonia is now obvious (Figure 1).
Research trials on Sunshine Golf Course have been providing excellent data on product testing for dollar spot. In addition, the exceptionally conducive environmental conditions for development of brown patch have allowed us to monitor effects of the products on both diseases. Untreated plots in all replications on July 15 showed greatest disease pressures at 40% brown patch and 15% dollar spot. Visible symptoms for brown patch were most severe on untreated plots as expected (Figure 2).
Of fungicides, the 21 day interval of the Emerald treatment at 0.18 oz had highest brown patch visibility at 20%, which when compared to the control was still far less. Other treatments that showed amounts of brown patch were Chipco26GT (dicarboximide family), Insignia (QoI), and the 14d low rate of Reserve (chlorothalonil + DMI). The fungicides that performed well with no visible symptoms of brown patch disease have been Daconil Ultrex (chlorothalonil), Honor (QoI
+ carboximide), Concert (chlorothalonil + DMI), Insignia, Renown (chlorothalonil + QoI) and Reserve (chlorothalonil + DMI) at both the 21d and the 14d high rates.
Treatments that have provided the best dollar spot disease control so far include: Daconil Ultrex, Chipco26GT, Heritage + Daconil, Insignia, Concert and Reserve at 21d (high rate). Treatments of Emerald, Honor, Renown and Reserve at 14d (high and low rates) all provided good levels of disease control. All fungicide treatments provided acceptable levels of quality except for Concert, appearing off-color (due to the DMI-propizole) and with coarser visible leaves.