July Got Hot! High Disease Pressure, Dollar Spot, Brown Patch, Summer Patch and Research on Tees

July got hot! It was a nice break, but it didn’t last for long. We are now back in familiar territory — peak midsummer heat. The National Weather Service put it this way about mid-week, “Sweltering summer heat will continue to produce very dangerous conditions through the upcoming weekend in several locations across the U.S. excessive heat warnings and heat advisories are in effect today across the East, in the South and for parts of the Southwest.” In other news, I’ve been noticing hydrangeas in full bloom for a while. Even in midsummer you will see them looking good when others — well not so much. A favorite is H. macrophylla ‘Annabelle’. Often affectionately called mopheads.

Image 1. Shehbaz Singh uses a stimpmeter to check the green speed of a large practice putting green with 777 creeping bentgrass, Bob Berry Sunshine Course, Lemont, IL. Settle, Jul 21, 2022
Figure 1. Map of current heat advisories (orange) or excessive heat warnings (purple) in the United States. National Weather Service, Jul 21, 2022

It turns out were are all now experiencing a hot summer in the United States. Not unexpected. What’s unexpected? Extended periods of oppressively hot weather (highs exceeding 90s and 100s). Thankfully the upper Midwest has not received a color on the map (a heat advisory) yet. Now is a good time to revisit what golf course surfaces (greens, tees, fairways) are made of. If you are a golfer or a lawn and landscape enthusiast you’ll say cool-season turf. It just means our turfgrasses are adapted to cool environments. When we get hot, it can handle it as long as the duration of the heat doesn’t last for weeks. So far, regular cool-downs (breaks) have occurred this summer. “Keep pumping the breaks!” What we are all thinking/saying with regard to Mother Nature just about now.

Weather Recap (July’s 3rd week) by Shehbaz Singh, MS

Finally, our two Spectrum Technologies Watchdog 3000 Series wireless weather stations are fully installed. One weather station is at North Shore Country Club in Glenview, IL. This represents weather trends for the north Chicago suburbs. The second station is installed at the Bob Berry Sunshine Course which will provide weather patterns for the south Chicago suburbs.

Figure 1. A Hot Week: Weather conditions at Bob Berry Sunshine Course, Lemont, IL

Carbohydrate Metabolism in Summer

If you are looking at say creeping bentgrass and you are a turf scientist you aren’t thinking cool-season and instead you are thinking C3 turfgrass. It has to do with important differences in the way photosynthesis occurs. The optimum temperature for C3 photosynthesis is 59–77 degrees (think bentgrass or bluegrass), and the optimum temperature for C4 photosynthesis is 86–104 degrees (think bermudagrass or zoysiagrass). Midsummer is a time when C3 photosynthesis (energy production) isn’t as efficient as it should be. The end result? A process called physiological decline can and will come into the picture in summer (plant respiration exceeds photosynthesis). It usually begins about the end of July. Thankfully, plants have an ability to store energy reserves (carbohydrates). Think belowground. Think roots. That’s right, roots and other non-photosynthetic organs play an important role as a sink to put extra energy away for later. Hard work by superintendent and staff in one season (spring) pays dividends later in the next season (summer). Good job.

Figure 1. An imbalance between photosynthesis and respiration occurs each summer as temperatures exceed 90 degrees with respect to cool-season turfgrasses. Fry and Huang, Applied Turfgrass Science and Physiology

Factors Affecting Respiration adapted from Fry and Huang, Applied Turfgrass Science and Physiology

  • Respiration (energy consumption) has a higher optimal temperature than photosynthesis (energy production)
  • 25-75% of all carbohydrates produced each day are then respired or used by plants each day
  • A positive carbohydrate balance is the secret of how to maintain good plant health
  • Any environmental condition or cultural practice that reduces carbohydrate production in photosynthesis or increases carbohydrate consumption will have a negative effect on plant health
  • Did you know? Nitrogen fertility is long-known to reduce carbohydrate levels (both growth and respiration are stimulated by N application)

High Disease Pressure — Dollar Spot (Clarireedia jacksonii)

This is the time of year when fungicides are necessary. For example, in a week we have experienced the most dollar spot pressure on creeping bentgrass greens that we’ve seen this growing season. It can be difficult to know exactly what this might look like, unless you are doing research and have several “untreated checks”. It turns out in turfgrass science we do some of that.

Image 1. Dollar spot damaging a creeping bentgrass nursery green. A randomized complete block design with 4 replications. Experimental plot size is 4 ft by 6 ft and red spray paint dots are used on corners to frame each plot. Treated (bleached white rectangles) versus untreated (green, healthy rectangles) in a fungicide study, North Shore Country Club, Glenview, IL. Settle, Jul 20, 2022
Figure 1. Dollar spot: Disease is at highest levels we’ve seen all season in Chicago. Seeing good results in a Providence plus L-93 creeping bentgrass nursery green study at North Shore Country Club in Glenview, IL. Using a 1/2 rate of Daconil Action (2.0 fl oz per 1000 sq ft every 14 days) we are seeing improvement in efficacy by adding a product called Activo (activator adjuvant with pigment) by Precision Laboratories.
Figure 2. Visual quality: A dollar spot study using a Providence plus L-93 creeping bentgrass nursery green at North Shore Country Club in Glenview, IL.
Figure 3. Normalized Difference Vegetation Index: A dollar spot study using a Providence plus L-93 creeping bentgrass nursery green at North Shore Country Club in Glenview, IL.

Brown Patch, Rhizoctonia solani

Our second most common foliar disease appeared in good form this week in Illinois. Right on schedule. Brown patch is most severe when nighttime temperatures are above 68 degrees with extended periods of leaf wetness (10 hours or more). Sound familiar?

There is an excellent weather-based predictive model out there by Dr. Mike Fidanza and Dr. Peter Dernoeden. It appeared on the scene about 1997. The model uses minimum temperature and hours of relative humidity over 90% to predict brown patch outbreaks. I used it. I was cutting my teeth on a MS research project back then. The big thing you learn with brown patch is to watch for extended periods of leaf wetness. If dew/guttation exists before you go to bed, well that’s great for research, but not good for your lawn. So always remember to not irrigate in the evening hours (around dinner time) otherwise you are just tacking on extra hours of leaf wetness which generally begins at midnight. You don’t want Mr. R. Solani too happy. That first name isn’t Roger.

Image 1. Scouting for BP: First brown patch on a creeping bentgrass fairway. Scouting by a superintendent revealed large off-color patches developing. Bloomington Country Club, Bloomington, IL. Harstad, Jul 21, 2022
Image 2. Scouting for BP: First brown patch on a creeping bentgrass tee. Initial development can be hard to see, but it helps to look for an outer smoke ring (above my right shoe). Settle, Jul 18, 2022

Summer patch, Magnaporthe poae

A chronic root disease of bluegrass is now beginning to see some action as well. Symptoms develop as circular patches or rings of chlorotic turfgrass that are 1–3 inches in diameter or as I like to say, “patches are up to about the size of a cup-cutter”. Preventive fungicide applications are usually applied in the spring or early summer when soil temperatures are 65–68 degrees. This does not mean you will see 100% control. Instead it means you should see good suppression, but there are a number of other factors that will dictate efficacy.

The first factor is reality. Factor 1) This is primarily a root rot disease (affects crowns too) and our ability to place fungicides in the root zone is difficult most of the time. So, it’s not surprising in the summer you often have to call an audible (apply a labeled fungicide and then immediately water it in to the depth of roots.

Factor 2) The weather. Anytime soils receive abundant rainfall you will probably be dealing with a level of root rots because they are of a chronic (always there) nature. Wet summer soil conditions will really drive this disease.

Factor 3) Which brings us to the third factor, best cultural practice? Reduce compaction in areas of high traffic (think golf green collars, surrounds, approaches and mower clean-up laps) which leads to increased soil moisture and reduced root biomass.

Summer Patch is favored by: Four (bad) things — some of those we can fix!!!

  • Hot, humid weather
  • High soil moisture
  • Low mowing heights
  • Soil compaction
Image 1. Summer patch negatively impacting the Poa annua portion of a creeping bentgrass green. Compaction via equipment and golfer foot traffic play a significant role by exacerbating symptoms of this root rot disease. Settle Jul 18, 2022
Image 2. Close up of summer patch in the Poa annua portion of a creeping bentgrass green collar. Settle, Jul 18, 2022

Golf Tee Research by Shehbaz Singh, MS

As a part of the renovation project at the Bob Berry Sunshine Course in Lemont, the golf tees were seeded with different types of cool-season grasses to check their performance. Previously all tees were seeded to creeping bentgrass (2004). In order to evaluate new turf species and cultivars, all previous bentgrass tees were treated with glyphosate to get complete eradication (2020). This week, we investigated the quality of different tees with visual estimation of turfgrass quality and with NDVI using a handheld GreenSeeker device (Trimble Inc). Data was collected from three lengthwise sections of each tee on July 19, 2022.

There were clear differences among the different golf tee turfgrasses. Both the visual quality and NDVI readings were higher for creeping bentgrass cultivars comparatively to all others. Creeping bentgrass cultivars such as PC2 and Piranha appeared to be offering a better golf tee surface. Poa annua was the main off-type observed in the creeping bentgrass tees. The Flagstick creeping bentgrass tee was negatively impacted by ant mounds. The Musket colonial bentgrass tee had poor visual quality and NDVI readings due to low turfgrass density which enhanced the encroachment of weeds like crabgrass.

Kentucky bluegrass tees also had good visual and NDVI readings but were lower than creeping bentgrass. However, the important observation on the Kentucky bluegrass tees is that they had been contaminated by creeping bentgrass. In a short period, time creeping bentgrass has found its way back and about 40-60% contamination was observed in those tees.

Tall fescue and perennial ryegrass tees tended to be the poorest performers according to visual quality and NDVI. Due to the bunch-type growth habit of these species, turfgrass density was low and areas of small bare ground patches existed. Weeds observed in these tees were Poa annua and crabgrass covering about 20-30% of the area. Residual Pythium blight damage in 2021 on the perennial ryegrass tee likely resulted in a greater presence of weeds.

Figure 1. Visual quality ratings (1–9, 6 is minimum acceptable) of different turfgrasses used as tees, Bob Berry Sunshine Course, Lemont, IL. Jul, 19, 2022
Figure 2. Normalized Difference Vegetation Index (NDVI) data of different turfgrasses used as tees. A higher number indicates better overall turfgrass quality. Bob Berry Sunshine Course, Lemont, IL. Jul, 19, 2022

Final Photo

A midsummer example of a C3 turfgrass lawn (Kentucky bluegrass) versus a volunteer C4 lawn (smooth crabgrass) in Evanston, IL. Settle, Jul 20, 2022



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Dedicated researchers and turf pathologists working for golf course superintendents in the Chicago area.