Another Round of Cold Weather!

In January and early February, we all deal with the waves of cold fronts that dip down from the Canadian Arctic.  However, as many growers are in full swing with bloom or have just started, these cold waves keep us all up at night.

At Citra in one of our plots that has some bloom occurring, we have turned on the water on the following dates:

  • Tuesday, January 7th
  • Friday, January 17th
  • Saturday, January 18th
  • Sunday, January 19th
  • Wednesday, January 22nd

We will continue to monitor tonight (Friday, January 24th) for cold weather, since it looks like the wind will be dying down.  The graph below details the actual temperatures for the Gainesville Regional Airport (KGNV) which is a few degrees colder than what we observe in our research plots at Citra.

This graph shows the minimum temperatures for January for Citra – and you can find out this type of information for a FAWN station near you with this link:

2014 Citra Minimums


What are some tools that you can use to help decide when to turn the water on?  One thing I can offer – the wind will almost always kick the temperature up a degree, so be on the lookout and carry a good thermometer with you as you are driving around the orchard.  Your car thermometer may not be the most accurate, so don’t count on that.

Good luck tonight, and stay warm!


What Does the Extension Service Do For YOU?

I received this forward from a colleague this morning –  It’s an article about how agriculture extension, the National Institute for Food and Agriculture (NIFA), and the Farm Bill all affect our lives on a daily basis even though we may not realize it.  (By the way, it’s from a great magazine called Wired – and it’s my husband’s subscription.  Which explains why I never saw this issue…magazines disappear in my house.)

Kudos to the author, Gwen Pearson for writing this article because although I am preaching to the choir for this blog’s audience, the majority of Americans don’t understand the extension service and all that we do.  My daily routine does have a lot of computer time, and not as much field work or face time with growers as I would like.  However, as extension specialists, our goals are to conduct research that addresses production challenges in the region/state and crop that we work with.  But, without stable funding, most of our time is spent writing grants to fund our applied research and support the people that help us do that work.  Deep down, all of us in extension really want to help people. (I would love to be a nurse, but I can’t stand blood or hurting people).

In this time of extra reporting for government jobs, it’s often difficult to write discrete statements about what extension accomplishes on a day by day basis.  We in extension, are often modest individuals that don’t trumpet our successes, yet – we are bearers of economic successes.  It’s the extra information that we deliver that helps a grower make decisions that result in profitability.  Yet, we in extension are not the first ones they call when they make that extra $1,000 per acre or 25% increase in yearly profits because of the information they received from the extension service.  Yet these success stories are exceedingly important to our progress reports for our Universities and States/National government that fund Extension through Smith/Lever funds and Hatch research funds to prove we making an impact.

We are also the bearers of life-changing information – in our 4-H agents and health and nutrition programs.  Do you have a child that has sold an animal as part of the 4-H program?  Those funds that kids get are often used for college and other educational endeavors that maybe their families can’t fund themselves.  One lamb even sold for over $80,000!  University of Florida, and IFAS Extension in particular offer Solutions for Your Life like keeping your New Year’s resolution, or caring for an aging parent or spouse, or even transitioning farms to family members to keep agriculture alive in each generation.

Finally, we help citizens prepare for disaster and recovery.  One great example of this is the work that UF Extension did with members of the community of Live Oak to recover after the flooding damage caused by Tropical Storm Debby in 2012.  This storm sticks out in my mind because was the first big party with a bouncy house for my daughter’s fifth birthday, yet it was cancelled because of TS Debby.  Although it dumped massive amounts of rain, many people evacuated and were safe.  However, the storm caused significant damage and Suwannee County Extension worked with citizens to develop a recovery plan.

So, I guess the question is for everyone in our communities – what does the Extension Service do for YOU?

New Central Florida Peach Newsletter

I hope that everyone is now warming up as the “Polar Vortex” is pushed out to other parts of the globe.  I, for one – am very glad that it did not get as cold as predicted here in the Gainesville area and where the bulk of my research plots are located.

The latest Central Florida Peach Newsletter has been published, and in it is information on great topics:

  • Frost Protection
  • Peach Borers
  • Fertilization Rates for Mature Orchards
  • Roundtable Event, January 14th, 2014 at the Pasco County Extension Office, Dade City, FL

Please be sure to RSVP so that they have enough lunch for everyone – and thanks to Ryan Atwood and Keyplex for buying lunch!

Cold Weather Coming!

Well, here we have our first real freeze of the season, and with many of the growers down south being in bloom, all will have to be vigilant as we head into Monday (1/6) and Tuesday (1/7) nights.  See below for information from NOAA weather:

For an article on how to utilize frost protection best, Mr. Chris Oswalt (Polk County Extension Agent; Regional Citrus Agent) wrote a great article in the last “peach” section of the Florida Grower.  See this link for information:

In addition, there are a number of extension documents that address freeze protection for peaches and other perennial fruit crops:

And finally, as a reminder, here are the temperatures that are important for each peach bud stage – depending upon how far along you are in the flowering/bloom period.

Peach Bud Hardiness Stages (WSU)

It’s important to note that the further along the flowers are (say first pink vs. full bloom) the flowers are less tolerant to low temperatures.  If you have questions about whether the flower buds are alive or dead, a publication from Colorado State has some great images:  If you make a cut laterally down the buds, you should cut through the flower ovary and see the pistils.  If they are green, then everything is alive, but if you see any brown tissue, the flower is dead.

Determining the amount of damage to your flower buds is easy; go through the orchard and collect several branch samples. Then you can cut through each bud and count the number of alive and dead samples to get a good assessment of cold damage to buds, flowers, or fruit.

In Citra, we have an expected low of 20°F on Monday night, with blustery conditions.  The wind speed is predicted to be between 13 and 15 mph, and we are just at bud swell, or a little beyond.  Although we will be keeping our eye on the weather, I am still unsure of what we will do.  My training tells me that it will be too windy and it will be difficult even for our high volume overhead sprinklers to keep up and get a good even ice coat on the branches. However, the next night it will be 25°F and again, depending on the stage of flower development, we may turn it on, since the wind will be much calmer.

One other graph we often look at to help us make decisions is the NOAA Hourly Weather Forecast Graph – so be sure to look at this chart to help you for your location.


Good luck!  If you have any questions, be sure to e-mail me at

Central Florida Peach Roundtable

Hi All – Just some details about the next C. Florida Peach Roundtable:

Please mark your calendar for Tuesday January 14, 2014 from 10am to 12pm at Pasco County Extension office (Clayton Hall) for the next Central Florida Peach Roundtable.

Our tentative speaker for this Peach Roundtable is Dr. Jose Chaparro. The topic and other information will be published on January 1, 2014 in the newsletter. So please be on the lookout for your copy of the Winter Edition of the Central Florida Peach Newsletter at that time.

Happy New Year to you all!

Dormancy and Early Bloom to Start 2014

How is it that our peach trees are already blooming in the south central part of the state?  It seems like we are too early by at least three weeks in many cases.  It makes for a busy holiday season watching our weather to make sure that we stay on top of frost protection.  A current analysis of the chill accumulation across our state doesn’t look good – keeping in mind that last year was also a warm year and winter.  See AgroClimate:

Accumulated Chill Units in Florida, January 1, 2014.

As a grower, what is there to do?  Well, first I think it would be good to start out with an explanation of the types of dormancy that perennial trees go through (Lang et al., 1987). 

Growth cessation and dormancy in peaches is driven by reductions in the photoperiod.  Photoperiod is the amount of light that we get during the day vs. the night period, and as we approach the autumn, the light period decreases and the peach trees respond to this by dropping their leaves (defoliation). 

Ecodormancy is where the tree stops the visible growth process and goes into a reduced state of metabolic activity because of an environmental stress.  This could be water stress (we shut off the water around the 1st of November to hasten this process) or cold temperatures (happens up to the north quite a bit). 

Paradormancy is a type of dormancy where physiological factors outside of the bud affect its growth and development, and this might be the production of auxin (a plant hormone that contributes to apical dominance), or a reduction in photoperiod during the season. 

Endodormancy is a period of dormancy that is induced within the flower or vegetative bud, and typically includes chilling responses and photoperiodic responses.  We see this type of dormancy affect vegetative buds, when we don’t get enough chilling and the resulting response is delayed vegetative bud break, or leafing. 

There are two main types of chill accumulation models that can help growers to track units of chill that are accumulated at night.  One is the standard chill accumulation model and the other is the Utah chill accumulation model

The standard chill accumulation model is one in which 1 hour at a temperature less than 45°F (7.2°C) equals 1 unit of chill accumulation (Weinberger, 1950).  In this model, any temperature, even those below 32°F are considered temperatures at which chill units are accumulated.  However, this doesn’t work that well for peaches, and a researcher in Utah working with ‘Elberta’ and ‘Redhaven’ peaches delved deeper into this subject and devised a second model (Richardson et al., 1974). 

The second model, and the one which we use for peaches, is called the Utah chill model.  In this model, an ideal range for chill accumulation was established for peach buds to come out of “endodormancy”.  For each hour at the following temperature ranges, a chill unit, or portion of a chill unit is accumulated.  These temperatures are:

chill table

In the Utah chill model, you can see that there is an ideal range at which 1 chill unit is accumulated, and then portions of chill units are accumulated at higher and lower temperatures.  So, although we may be above the ideal range (36.5 – 48.4°F), we still have the opportunity to accumulate half-units of chill during our warm nights in Florida.  However, the caveat with this model is: if it is too warm immediately after chilling is accumulated, warm temperatures can negate the chilling from the previous two nights.  Chilling accumulated prior to this warm period and the previous 2 nights remain valid within our working model. 

We can also observe fruit set problems when these warm nighttime temperatures occur during the bloom period with some of our peach varieties, notably, ‘UFOne’ and ‘UFBeauty’ in warm areas of Florida. 

The AgroClimate site which covers chill accumulation ( offers two options when you choose a weather station:  <45°F, and 32-45°F.  Although not quite within the ranges that we need to calculate the proper chill accumulation with half-units, the 32-45°F model does a pretty good job of an estimation.  So, be sure to choose this one when tracking your chill unit accumulation this winter. 

For those of you that use Weather Underground, I found a neat tool that calculates the chill accumulation for a particular station.  It’s called Get Chill Hours! (, and calculates the chill accumulation with three different models.  One caution:  when the model calculates the Utah Chill Model accumulation, it will most likely be negative because of our warm nights interspersed with our nights that accumulate chill.  Thus, the 32-45°F is again a better depiction of our chill accumulation with certain caveats as mentioned in the Utah Chill Model explanation. 

Results of Low Chill Accumulation?

So, now understanding some of the background about dormancy, you can see that in South Central Florida with our low-chill peach varieties, trees in most years appear to not enter into endodormancy, which can hinder the ability of the tree to push vegetative buds when they should.  Observation of trees in commercial orchards indicate that trees enter into ecodormancy in late October and early November when irrigation and fertilizer are reduced in the orchard. 

Warm temperatures during the past three years in December have resulted in trees flushing and blooming approximately December 15th without significant accumulation of chill units.  Fruit set in varieties like ‘UFSun’, ‘Flordaglo’, ‘UFBest’, and ‘TropicBeauty’ has been excellent under these conditions. 

The result of not leafing shortly after bloom or having the delay of the vegetative buds push, is that the tree must rely on stored carbohydrate and nitrogen reserves to produce fruit, and both cell division (which affects fruit size) and the cell enlargement (when sugars and peach flavors get transported and develop in the fruit) can be reduced, ultimately producing a “flat” tasting fruit.  The leaves, through photosynthesis, produce the sugars and flavor compounds needed to give the fruit that “tree-ripe” flavor that we sell to the consumers. 

A second result of low chill unit accumulation is an extended bloom period.  This results in an extended fruit set period, and thus thinning must be done several times during the late winter/early spring, rather than once during the thinning period.  Multiple trips through the orchard results in more labor dollars spent, reducing the orchard’s bottom line. 

What can be done?

All of this is wonderful information, but how will it affect how we grow this year’s crop?  In years with low chill unit accumulation like this one, experience tells us:

  1. The trees will bloom early.  Be sure that your frost protection systems work, and you are ready for any cold fronts that sweep down the state. 
  2. Because the trees are blooming early, if you have >50% bloom, start watering and fertilizing.  Stress during the fruit set and cell division period will result in fewer and smaller fruit. 
  3. Be sure to know what your fruit developmental period (FDP) for your peach variety.  These ranges still hold true for overall fruit development, but cool, rainy weather during the spring will delay any gains in the bloom period that we have achieved.  In addition, if you bloom around January 1st you will most likely harvest ‘UFSun’ around April 1st.  But, if you bloom around January 20th, then you would probably harvest ‘UFSun’ around mid-April – because it is warmer from Jan 20 – April 15th then from January 1 – April 1st.  Warmer temperatures will compress the fruit developmental period. 
  4. If you have fruit on the trees, start your disease and insect protection programs along with your irrigation and fertilization programs. 

In the future, we hope to gain some knowledge about the use of rest-breaking chemicals like hydrogen cyanimide (Dormex® or BudPro®); however, with the products there is a great potential to do significant bud or branch damage with high concentrations and/or application at the wrong time.  In cooperation with a few growers around the state, I’m tracking the results of various applications and rates and will have more to report by the end of this year. 

Cheers and Happy New Year!


Fraisse, C. and A. Whidden.  2010.  Chill accumulation monitoring and forecasting.  Available at:

Lang, G.A., J.D. Early, G.C. Martin, and R.L. Darnell. 1987. Endo-, para-, and ecodormancy:  Physiological terminology and classification for dormancy research. HortScience 22:371-377.

Richardson, E.A., S.D. Seeley, and D.R. Walker. 1974. A model for estimating the completion of rest for ‘Redhaven’ and ‘Elberta’ peach trees. HortScience 9:331-332.

Weinberger, J.H.  1950.  Chilling requirements of peach varieties.  Proc. Amer. Soc. Hort. Sci.  56:122-128.