Tech Tip: Drought Stress

 “I don’t have drought stress!  I water!”

Have you been hearing that (or something close to it) from customers lately?  How do you deal with a complaint like that?  Let’s start with the realization that their lawn may be many inches below normal in natural rainfall right now.  Second, an irrigation system is never a replacement for natural rainfall, but rather a tool to augment the rain that actually does fall.

As you can see in the above graphic, many parts of the country are affected by drought conditions.  Although it rained a little bit at the end of this past week, that will not dramatically change things.

So when a customer says that they cannot be suffering from drought stress because they are watering, remember this: the only determining factor as to whether a lawn goes into drought stress is how much water is in the soil.  The customer’s impression that they are watering sufficiently has no bearing on observable facts.  The only way to determine if a lawn is in drought stress is to look at how much water the lawn has available to it.  This is done with a soil probe, a tool that each of our lawn specialists has in his truck.

 

On the left is a “T” shaped soil probe inserted into a drought stressed lawn.  On the right is the core pulled by the soil probe and you can see that the soil is extremely dry.

Let’s break this down a bit to get a fuller understanding of what’s going on here.

What is drought stress?  It is the reaction of the turfgrass plant to insufficient soil moisture, usually leading to the plant going into dormancy (a period of rest where it is alive but not actively growing).  We observe dormancy in turfgrass by noticing that they lawn is uniformly brown.

This is different from heat stress, the reaction of the turfgrass plant to high temperatures (anything above 75 degrees for cool season grasses, increasing in severity as the temperature increases).

A lawn can be in a state of drought stress without being in heat stress.  For instance, think of a time in early spring when it is cool and not raining.

A lawn can be in a state of heat stress without being in drought stress.  For instance, think of a day when the temperatures are in the high 90’s but there are thunderstorms going through.

Or the lawn can be suffering from both heat stress and drought stress.

An irrigated lawn can be in drought stress due to a malfunction in the irrigation system.  A broken pipe or sprinkler head will deprive an area of water, causing browning.  Sometimes grass will grow over an irrigation head, blocking the water leaving the sprinkler.  Other times, the irrigation system was not designed properly and there are gaps in the amount of water that is applied.

Here’s a perfect example.  This photo shows an irrigated lawn with healthy green turf in the foreground and brown stressed turf in the background.  Curiously, there are three or more splotches of green in the middle of the stressed area.  What’s happened here is that the irrigation system has malfunctioned (broken pipe, broken head, broken valve…).  These sprinkler heads pop up and dribble water instead of covering their intended area, thus we have drought stress on an irrigated lawn.

Another thing to consider is that during summer weather conditions lawns can use anywhere from 1” to 1 ½” or more of water per week.  If the irrigation system is not delivering that amount of water, then the lawn will respond to the deficit by going into drought stress.  Once again, we have drought stress on an irrigated lawn.

It’s not that the customer is wrong; it is that they do not understand the intricacies of dealing with lawns under difficult circumstances.  It’s up to us to educate them!

What can we say to educate our customers?

  • Embrace the Brown!  Lawns that do not get enough water go dormant, which is completely normal and recoverable.
  • Don’t mow unless necessary.  If you do have to mow, use a sharp blade, mow as high as possible (3 inches plus), and avoid mowing during midday hours or during periods of high temperatures to avoid causing tire marks.
  • Research has shown that lawns can survive drought successfully with as little as 0.25” of rain over a six-week period, often longer than that.
  • Fall aeration and overseeding are great ways to prepare your lawn for future stresses.  The aeration allows for better water infiltration, better exchange of gasses with the atmosphere, increased decomposition of thatch among other things.  Overseeding introduces new grass plants that will take over for any that did not survive the drought.  New grass plants are naturally more competitive that older plants and often have greater resistance to drought.
  • What’s the worst thing a customer can do right now?  Skip their scheduled applications!  When we are told to skip our applications, we do not have the opportunity to spot treat for summer annual weeds like crabgrass, do not have the opportunity to monitor for insects and disease, and do not have the opportunity to apply the fertilizer that the lawn will use when drought conditions break and growth resumes.  Lawn care is all about looking ahead, not what’s going on right now.  Skipping is the worst thing they can do!

Find more technical tips in our Technical Resource Library in the NALP Member Center.

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