It has been three weeks since we pulled our test plugs and the results are mixed. The good news is our bentgrass plug continues to fill in and look pretty good. The bad news is both of our ryegrass plugs have shown little-to-no signs of life. Although I am disappointed by our results, I am not all that surprised.
Bentgrass on top and ryegrass plugs on the bottom
A common thought is that the turf has succumbed to desiccation, but in the case of our ryegrass, I am unsure if that is our main culprit. Without a doubt, the dry, open, and windy winter has caused a great deal of stress on the plant, but I am quite certain that the majority of any turf loss will be attributed to direct cold temperature injury.
FAQ's about cold temperature injury
What is direct cold temperature injury?
Direct cold temperature injury occurs when the crown of the plant takes up water through a process know as crown hydration. Crown hydration occurs naturally when the plant experiences periods of warm weather during dormancy. If a dramatic drop in temperature follows this hydration process the water within the plant rapidly freezes and punctures the cells of the plant. This most often results in plant death.
Why does the ryegrass show signs injury and the bentgrass does not?
All species of turf grass have different LT50 temperature thresholds. An LT50 is a temperature threshold at which you can expect 50% of the turf to die when exposed for a period of time. The LT50 levels for the dominant turf grasses on our course are listed below:
Ryegrass: 5°F
Bluegrass: -23°F
Bentgrass: -31°F
You can see that ryegrass has a very high LT50 temperature when compared to the other cool season turf grasses. This is due in part to its genetic predisposition to rehydrate much quicker than other turf species.
What made this winter worse than other?
We have had 31 days with a low of 5°F degrees or less at the course since December 1st. Remember from above that the LT50 level for ryegrass is 5°F. We also had three instances where we had a 60+ degree swing in 48 hours or less and one instance where we had a 50+ degree swing in that same time frame. Again, remember from above, that ryegrass quickly initiates crown rehydration in the presence of warm weather. All of this is on top of the fact that we had no snow cover for insulation. We were also extremely dry and there is thought throughout academia that there may be a synergism between drought stress and cold injury.
Why did the turf cut at higher heights survive better than the turf cut at lower height? OR Why did my lawn survive but the fairways struggled?
The answer to this question is a bit dynamic. There are a lot of factors that effect how our golf course overwinters versus how a home lawn overwinters. The simplest and most common reason for this is that most home lawns will consist of bluegrass and fescues, not ryegrass. Due to a number of reasons, ryegrass is not a great choice for home lawns, thus, is not used in this setting very often. Fescues and blues have a better cold tolerance than rye. Another reason the longer turf survives better is the insulating property of the longer leaf blades. It doesn't take a lot to change the micro climate at the crown level. A few inches of leaf blade can trap heat, keep out the cold and block out wind. A few degrees difference or a little protection from the biting wind can really make a difference.
What are our levels of damage on the course?
This is very difficult to predict. Its is hard to make a blanket statement about the condition of 60 acres of ryegrass based on 1/2 of a square foot of turf grown in a bucket. What I can tell you, regardless of the extent of the damage, is that a comprehensive recovery plan is already set up and we are prepared to tackle any level of injury.
The next few weeks will be very telling. What we need now is warmth, sun light and moisture.
