During the summer of 2015, I initiated a discussion about summer patch on Kentucky bluegrass sodthat was severely affected by summer patch. The thesis of the initial article was that fungicides applied after the outbreak of symptoms (July 28) were not effective in reducing disease severity. Figure 1 shows the experimental site at the time of the application. By mid-autumn (October 15) symptoms were largely masked by natural turf recovery (Figure 2). The sward showed no indication that any treatment suppressed symptoms, and upon close inspection, abnormal growth due to disease was evident (Figure 3).
Fungicide was applied again recently (May 25, 2016), when symptoms were just beginning to show. One week later, after little precipitation (0.3 in) and above normal ambient temperature, symptoms were in full bloom. Figure 4 shows the current state of the experimental site–the faint white lines outline our fungicide plots. I would add that this level of symptom expression is unusual for mid-late spring in the Midwest–attributable to a 4-week period with meager precipitation (0.9 in) during which plants with compromised root systems were unable to sustain normal growth.
I think these observations relate to the frustration often experienced by lawn care professionals, who struggle to manage turf with fungal root infections. Poa species are cursed with susceptibility to root infecting fungi. Of course, some cultivars seem less susceptible than others, but where inoculum is plentiful and soil temperature and moisture favor pathogen activity, disease will occur. It is only a matter of time before periods of environmental stress reveal the true extent of root infection.
Check out: Summer Patch Revisited
Controlling a severe outbreak will require an integrated approach—fungicides to limit infection, and cultural practices (including nutritional supplements) to relieve stress. Stay tuned for “Summer Patch Part 4”…maybe in another 8 weeks.