winter

Prepare Now for the Winter Season

Daniel Cooper freeze

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Microsprinkler irrigation provides a protective layer of ice on a satsuma tree.
(Photo by Doug Mayo)

By Maegan Betty

As the cooler months start to arrive, it is important to protect citrus trees from overnight freezes and extreme weather conditions. Last December, the All In For Citrus podcast addressed what cold protection should look like for Florida citrus growers in an interview with Chris Oswalt, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) citrus Extension agent. Excerpts from the interview follow:

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Chris Oswalt

Q: What were some of the impacts growers experienced from freezing temperatures in January 2022? 

A: There were two Monday mornings toward the end of the month that it got pretty cold, and there was some frost. We had some defoliation, and we had some instances where some wood was split by the low temperatures. It did not affect the trees, per se, but we did have some small wood that got split. There was some damage to the new flush and the flowers that were exposed to that frost. But I did not hear of any significant fruit damage.  

Q: Some growers said the freeze snuck up on them. Did you hear that, and are there ways that they can guard against that in future cold events? 

A: I would say the best thing is to find a reliable source of weather information, wherever that may be, whatever source you use, just as long as it is consistent. That is probably the best advice that I have. Depending on the type of freeze, you can go into situations where the freeze is going to develop a certain way, and then later in the evening, things change a little bit, and that can have an effect. You really can’t let your guard down. Have a consistent source of reliable weather information for which you can base the conditions that are going to occur in your grove off of that forecast.

Q: Growers now have their own weather stations, but UF/IFAS also has the Florida Automated Weather Network (FAWN). How useful is that for growers in terms of staying ahead of the weather? 

A: FAWN stations provide you with real time weather data. I consider it very important in being able to determine what the actual conditions are that are occurring over an area and to compare those to the conditions that are occurring in your grove. The FAWN towers have the ability to measure ground temperature, temperature at 6 feet and temperature at 30 feet, which can give you a better idea of the development of an inversion.

You can look at a group of weather stations and see how a freeze develops overnight. There is specific development in these cold weather events — whether they be radiative or advective events — and you can glean a lot of that information over a larger area based on what these weather stations are recording.

Q: Commercial weather stations are getting pretty sophisticated in what they can do and track, correct? 

A: I believe so, and they are going to collect the normal parameters that you would be interested in. Of course, the thing that is of most concern during a freeze event is the wind blowing, so anemometers on a weather station are important to see if the wind is blowing or calm. You also have the air temperature, which is important, along with the dew point. If you are going to use irrigation or water for cold protection, you would definitely want be able to have a wet bulb temperature. That’s going to be provided by a good weather station today. 

Q: As the weather cools down, what are some things that growers need to do to prepare for winter?

A: You want to maintain the health of your trees going into the winter. With HLB, that is a lot more difficult than it used to be, but you want to try to maintain a level of health so that the trees are not water stressed or nutrient stressed. You obviously don’t want to do severe pruning in the middle of winter. You don’t want to have practices that encourage the trees during warm periods of winter to stimulate any vegetative growth because then they will lose their tolerance to cold.

If you are going to use water for cold protection, and you’re using microsprinkler irrigation, you would want to make sure your pump and your well station are all in good repair. You don’t want leaky lines or broken lines. 

Q: Any common mistakes that growers should avoid? 

A: It’s very important that you understand the potential for evaporative cooling if you’re going to use irrigation for cold protection. A mistake would be turning your irrigation system off too early or potentially having a situation where you might not get it turned on in time. You’re going to have to turn it on before you have any freezing occurring in the irrigation system. When it’s time to turn off the irrigation for cold protection, you’re going to want to know that it’s safe to do so. That’s when you need to have some information on the wet bulb temperatures and the evaporative cooling potential that may be occurring when you make these decisions.

Visit citrusindustry.net/allinforcitrus to hear the All In For Citrus podcast episodes.

Maegan Betty is an AgNet Media intern in Gainesville, Florida.

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