Necrotic Ring Spot and Summer Patch Active or Soon to be Active

Last updated 4/29/03

HOME

TURF TIP
4/29/03

Necrotic Ring Spot and Summer Patch Active or Soon to be Active

These diseases are caused by closely related root pathogens, they result in nearly identical symptoms (especially on greens that are largely Poa annua), and are managed with similar fungicides. I normally sort these diseases based on the time of symptom expression. Since the summer patch pathogen becomes active in warm soils (75 F at 3 inch depth), we are still 3 -5 weeks from summer patch infection and maybe 6-8 weeks away from the first indication of summer patch symptom expression on Poa annua. Necrotic ring spot occurs earlier than summer patch and the a patchy decline currently observed on bent/Poa greens is likely necrotic ring spot. This pathogen favors cool wet soils. Initial infections probably occurred in early April, with symptom expression a few weeks later (now). Fungicides for control of root diseases are limited to systemics (acropetal penetrants) including thiophanate methyl, DMI, and azoxystrobin. Opinions vary regarding drenching and spiking prior to application. The idea is to deliver the fungicide to the upper part of the root zone where it will be effective against the soil fungi. At the very least, one should apply the fungicide in 2 – 4 gallons of water per 1000 square feet.

Rick Latin, Turfgrass Pathologist