I'm Barclay Poling small fruits specialist at NC State in the Department of Horticultural
Science.
I want to talk to you about a very important instrument that we use for managing our frost
protection in strawberries.
I don't know many crops other than strawberries where this is used, but strawberry growers
have fallen in love with these for some good reasons.
This is a digital thermometer.
It's not inexpensive; it's going to cost you a couple of hundred dollars.
In the back of this digital thermometer is a jack, which attaches itself to a thermocouple
wire, which has a nice Teflon coating.
At the very end of this wire we can take the measurement of the air from these exposed
wires that have been twisted, there's about 1/3 of an inch of the Teflon was peeled back
to expose that area.
Right there where those wires are twisted together, that junction, we're taking the
air temperature reading.
Now, what we like about this device is not only can we take air temperature very efficiently,
but we can also measure the blossom temperature which is the most important temperature of
all.
It's been a problem for us for years and years to know exactly what the blossom temperature
is.
You can't always assume the air temperature and the blossom temperature are going to be
the same, and when they do diverge that can be real trouble for your decision regarding
when to start an irrigation system and when to safely shut off.
So I'm going to show you now how we use this thermocouple and handheld digital thermometer
to bring real precision to these decisions.
So first of all the air temperature right now is about 65 degrees, and sometimes the
air temperature can be higher, sometimes it can be lower than the blossom.
It has a whole lot to due with humidity in the air.
Rather than complicate things, I'm just going to tell you the most important temperature
you need to know is the temperature of that blossom.
Sometimes it is hard to get that from just a handheld type thermometer.
So what we're going to do now is take this thermocouple wire and insert it or stick it
right inside the bloom, and I'm going to show you how I do that.
I take a healthy blossom like you see here.
Generally, I pick a fairly large one because this thermocouple wire is fairly coarse, and
it needs to go into a larger bloom for this to be a successful technique.
What I do is I insert that wire just above the base of the bloom.
You see that nice yellow dome.
That's the part of the flower that is going to eventually become the strawberry fruit.
I'm going to insert this wire right into that tissue, and I'm going to leave it there.
I can take readings all through the night, exact readings, of what my blossom temperature
is.
So let's find out.
You notice what I did here?
I inserted that wire completely into the bloom, so that none of the wire is exposed to the
air.
Remember, I'm trying now to measure blossom not air temperature, so that is why you don't
want the wire exposed.
Today, let's just have a look and see.
The blossom temperature is fairly warm.
Sometimes we find, especially on frost nights when the air is particularly dry, the blossom
temperature can be 2 to 3 degrees Fahrenheit lower than the air temperature.
Now, that's a big difference, and when they diverge in that way you can make some serious
mistakes as to when exactly to turn an irrigation system on or when to turn it off.
Now, I don't have to be guessing about that, and I can look at this temperature.
Obviously, we're not in any danger here at 66 degrees, but we do know that a strawberry
blossom cannot endure temperatures much below 28 degrees Fahrenheit.
When you go below 28 degrees Fahrenheit, there is a big chance it will be killed, even in
a matter of 10-15 minutes.
So, we use this as a great tool to indicate exactly when the crop is going to be in threat
of the blossoms being killed.
When we reach usually about 30-31 degrees Fahrenheit on this digital thermometer, we
know it is time to get our irrigation system ready and begin to run it.