July 11, 2023: Disease Activity & Field Day Arrive! – Turfgrass Science at Purdue University

July 11, 2023: Disease Activity & Field Day Arrive!

Highlights: Events – Purdue Turfgrass & Landscape Field Day next week; dollar spot arrives with a flurry; smattering of brown patch; 1st Pythium root rot diagnosis on putting greens.                                        


Cool early summer temperatures and recent rainfall.

June temperatures were fairly mild in the region, with several mornings dipping into the refreshing 50’s for central and northern Indiana. Statewide and for much of the region, June temperatures ended a few degrees below normal for the month. The last few days of June and first full week of July flipped that trend with a few jaunts into the 90s, that along with some frequent precipitation sparked disease activity and the first round of summer stress to cool season grasses.  Rainfall events in late June and July thus far have reduced drought impacts on lawns in Indiana and have improved the outlook for much of the region. From April – June, much of Indiana and Illinois received 6-8 inches below normal precipitation, and some areas in Missouri were 10+ inches below normal (see detailed maps here). While still tough, turfgrass managers that controlled their irrigation were able to substantially reduce outbreaks of most diseases. All in all, this has been a very slow year for disease development and stress in the north central region, which should only be disappointing for a turfgrass pathologist.

Forecast: Summer temperatures take hold; random rain chances

Mid July temperatures are expected to rise with no more cool morning breaks apparent in the forecast over the next 6-10 days. Persistent rain chances, even if they don’t come to fruition, indicate humidity will be prevalent and heavy morning dews will remain. These environmental conditions will be conducive and ripe for sustained development of foliar diseases such as brown patch and dollar spot and could spell an increase in soilborne disease outbreaks on cool season putting greens.  

Dollar Spot Epidemic Explodes

Dollar Spot Pressure Explodes Just Before the 4th

Driven by high humidity and conducive temperatures, dollar spot finally arrived on the scene in our research plots and Kentucky bluegrass lawns and roughs north of Indianapolis. The outbreak coincided with the first persistent rise of probability of the Smith Kerns model above 20% and into the 40-50% range, which had not been observed since last year (https://turf.purdue.edu/turf-disease-prediction-tool/). Effective fungicide treatments were exceedingly obvious the morning of June 30th and have become more so in the last week on our putting green research trials. Kentucky bluegrass lawns are also being affected, with characteristic hourglass shaped lesions observed in tan to bleached out areas. On lawns, many sprayable formulations in the DMI and SDHI classes are available, but only granular formulations containing thiophanate methyl (3336), propiconazole (Headway G) or triticonazole (Pillar G) are labeled and effective for control.  

Brown Patch Smolders

First Brown Patch on Bentgrass & Tall Fescue in the last few weeks.

Brown patch outbreaks on creeping bentgrass and tall fescue have been observed ephemerally in early July, but fizzled out with low night temperatures. Over the next few weeks with higher temperatures expected, (and not so low lows), I’d expect brown patch to fully take hold here and throughout much of the region. Although brown patch can affect some Kentucky bluegrass cultivars (particularly ‘HGT’), the disease is much more prevalent on tall fescue. Although similar to dollar spot, brown patch lesions are often scalloped and irregular across the leaf blade and do not run directly across. Fungicides for brown patch control on lawns also differ, with the strobilurin chemistries being traditionally more effective than the DMIs or other chemical classes.

Pythium Root Rot – 1st Diagnosis of the SeasonFirst Pythium root rot diagnosis on putting green in southern IN

While much of Indiana has been dry, a few spots in southern Indiana and northern Kentucky received a gully washer or few in May and June. Saturated conditions at one of these golf courses sparked an outbreak of Pythium root rot, an old, unwelcome friend that is perennially the most diagnosed biotic disease on bentgrass putting greens. Stand symptoms are not a reliable diagnostic feature, and simply appear as collapsed, thinning out turf.  As opposed to Pythium root dysfunction, crowns and roots of plants affected with Pythium root rot are dark and necrotic, and numerous oospores are observed in affected tissue. The disease is often observed in older, high organic matter putting green soils that hold water and don’t drain well. Pythium, as an oomycete and not a true fungus, moves with motile swimming spores in these saturated conditions to rapidly infect new plants. Some of our previous research indicates irrigation from golf course surface waters may even add to the inoculum load, as Pythium was found in both the source and water coming from the irrigation heads. Fortunately, we have two fungicides, cyazofamid – Segway and picarbutrazox – Serata, that can be applied preventively for control or at higher rates in curative situations. The key is to water these fungicides in with at least 0.125 inch (preferably 0.2 – 0.25 inches) of post application irrigation since the pathogen and infection point is in the soil.


Purdue Turfgrass & Landscape Field Day next week!

Make plans to join us next week on Tuesday, July 18th to attend the Purdue Turfgrass and Landscape Field Day. A variety of topics from adjuvant use to cultivar performance, to equipment safety to irrigation to insecticides to tree issues will be presented by various presenters including the programs of Drs. Bigelow, Patton and Richmond, and various others. The turfgrass pathology team will be discussing the potential of interseeding new cultivars to enhance disease resistance, and joining Dr. Bigelow for an afternoon tour of walking the plots to discuss lawn care and disease prevention. Should be a great event and hope to see you there!

Register Here : 2023 Purdue Turfgrass & Landscape Field Day


2023 Lawn Care Diagnostic Training

 If you can’t make it next week, (or even if you can), also consider the lawn care diagnostic event to be held two weeks later on August 1. This training provides hands-on demonstrations geared to learning how to diagnose and solve the most prevalent management problems for lawn care professionals. Each participant receives a guide to the most common turfgrass diseases and for turfgrass weed identification and control.

Register Here: Lawn Care Diagnostic Training – August 1, 2023

Lee Miller

Extension Turfgrass Pathologist – Purdue University 

Follow on Twitter:  @purdueturfpath

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