By Jack Fry
Looks like we’ve got a short-term period of cooler temperatures over the next several days. Midsummer heat relief is good for us, and it’s also a great time to do some of the cultural practices we often avoid during midsummer heat.
Creeping bentgrass and annual bluegrass don’t like the heat, and really don’t appreciate it when we implement certain cultural practices during hot weather. On greens that have shallow roots and experience indirect heat stress, any kind of stress brought about with cultural practices can sometimes be the “straw that breaks the camel’s back.” Consider implementing some of the following during short stretches of cool weather:
1) Solid tine aerification. Opening up the surface of the green can help get oxygen to roots and prevent a “sealing off” of the surface that can arise when organic matter accumulates.
2) Verticutting. Using vertical knives to cut leaves and stolons is certainly a stress to the plant, and now is a good time to do it if your greens are grainy (a la Johnny Miller!), or are accumulating more organic matter at the surface than desired.
3) Sand topdressing. Topdressing during midsummer can be stressful to the plant especially if it the sand is dragged into the surface.
4) Product applications. Some products can potentially cause more injury to creeping bentgrass and annual bluegrass when applied during hot weather, including liquid fertilizers, plant growth regulators, wetting agents, and even some fungicides. Labels on some products specify temperatures in which they should be applied. Use the break in the temperatures to apply products that may be needed.
5) Mowing and rolling. If you haven’t done it yet, raise the mowing height if you can, and roll a few days each week instead of mowing. Having more leaf area is always a good thing for the plant.
Summer is really here now, with fireflies, trips to the swimming pool, and … hot south winds to suck the moisture out of the ground. In sand-based putting greens, localized dry spot can pop up FAST, causing major damage in a short period of time.
Here is what localized dry spot can look like:
Keep an eye on your soil profile so you can stop this damage before it starts. When you get damage to the extent shown in those two photos above it is a long road to recovery.
To check for localized dry spot, pull up some cores and use the “droplet test” by putting drops of water on the plug. If the drops just sit there, not wicking in, you have a problem. The soil is water-repellent.
Sometimes there is a defined hydrophobic layer with normal soil above and/or below, so check at different depths, all the way down the rootzone:
You might also notice water beading up on the surface and not wicking in.
You don’t want this to sneak up on you. Keep an eye on your soil profile, especially locations with a history of problems. Aerification and use of wetting agents can help get moisture where it needs to go.
This example below shows how a slight change in the rootzone can cause problems. The round spots are all locations where the soil was altered for research, with little mini-plots inside tubes sunk into the ground. These spots are prone to LDS. We all know that putting greens are pretty sensitive, so be careful if you are changing up your sand topdressing or other soil-related factors.
Our own Dr. Jack Fry is an expert on cool-season turfgrass physiology. He co-wrote a book on the topic:
and he developed an online GCSAA class (click HERE) as well.
So, every year, around this time, I end up asking him about mid-summer turfgrass decline. I asked Jack to write some thoughts for this blog:
In the midst of a summer with 100+ F temperatures, it’s worthwhile to consider some of creeping bentgrass’s preferences and management strategies that might be helpful to reduce its stress, and yours. See, the thing about creeping bentgrass on putting greens is….
- It came from Western Europe. You live in Kansas.
||Average July maximum temperature (°F)
||Average July minimum temperature (°F)
- Its roots die first, then its leaves. Keep the roots happy and you’ll have happy bentgrass and happy golfers.
- Its roots prefer to grow at 55 to 65 °F; root growth slows even as low as 80 °F. This summer, temperatures near the surface of greens have been over 100 °F.
- Faults with construction, drainage, management practices may produce a quality turf surface for 10 or 11 months of the year. It’s the one or two other months that cause problems. If you want to avoid bentgrass decline, then start with a good rootzone.
- Rootzones that hold water are warmer and also have less oxygen for root growth. If you don’t have an ideal rootzone, work to improve it in the fall and spring with aggressive core aerification and topdressing.
- The benefits of coring are often seen during summer stress. Why are there green polka dots within the brown turf? Turf in those spots has roots!
- Opening the green’s surface with small, solid tines or spikes can help with water infiltration and root growth during midsummer. Don’t overdo it – the turf is under stress.
- Although superintendents suspect (and often hope) that a disease is causing the problem in mid-summer, over half of the samples that are evaluated in our lab show no disease.
- In our climate, air movement across the surface of the green is critical for bentgrass health. If your greens are surrounded, let them free!
- Maximize summer airflow from the south, but also vent to the north (just like opening two windows to get cross flow in your house).
- Hand watering can be used to address deficiencies in water distribution of the irrigation system, target localized dry spots, and deal with inconsistencies in water retention and drainage in the root zone. It shouldn’t be overdone or underdone- train and use your best help for handwatering.
- Syringing refers to applying a light mist of water droplets to leaves only, and then relying upon evaporation of that water to help cool the leaf surface. How effective do you think that is on a humid, July day? Not very, unless you use a fan to encourage evaporation from the leaf!
- Trees use light for photosynthesis, so does bentgrass. If trees are shading the green, which is getting the light – the tree, or the turf?
- Cultivars that are more dense get less Poa invasion, and Poa is more likely to die during summer stress than bentgrass. Plant newer, denser cultivars to reduce Poa.( The photo shows Poa checking out in the heat.)
- Light applications of nitrogen can be beneficial during heat stress (0.10 lb. N/1,000 sq. ft.)
- Newer cultivars have been shown to be more heat tolerant than Penncross, but even these will experience decline during prolonged heat.
- Clean up laps are often the first to show symptoms of stress. Why? Excessive traffic and wear. Have you considered a dedicated mower with a slightly higher mowing height for the clean up lap? Do you skip clean up laps on some days?