Alabama Chilling Crisis Information

20 January, 1999

Alabama peach growers are facing a serious crisis as a result of the 1998-99 winter weather pattern that has resulted in what may prove to be a record shortage of chilling.  Georgia, South Carolina and Alabama have made application for state labels (24C) for application of Dormex on peaches, nectarines and blueberries to help overcome the shortage of chilling hours being experienced this winter.  It is hoped the Alabama label will be issued by January 21, 1999.  Georgia and South Carolina have already issued their state labels.

To assist producers in determining when and how the growth regulator, Dormex, should be applied to peaches and nectarines to help overcome the current chilling problem, I have prepared special information which is described below.  For an explanation of what Dormex is and its use, you are referred to the option on this home page entitled "Action Program for Dormex Application on Peaches".

Based on forecasts for late January and the month of February, less than average chilling is anticipated across the state for the remainder of the winter.  My best estimate is that extreme southern counties (Mobile, Baldwin and Houston) will have only received 375 to 475 hours by February 15.  Central counties (Chilton) will probably be fortunate to receive 750 to 800 hours by February 20 to 25.  These estimates could go higher if another cold pattern developes across the Southeast, but it doesn't look promising.

Appropriate comments relative to the safe and effective use of Dormex on peaches and nectarines in the state will be provided in this "Commentary" on a regular and timely basis.

Dormex will probably not be needed on blueberries in central counties but may become essential in southern counties.  Most rabbiteye blueberries being grown have chill requirements of 400 to 650 hours at or below 45 degrees F.  Most studies conducted on Dormex use on blueberries has been completed in Georgia and Florida.  A rate of 1 to 1 1/2% should be used on plants while fruit buds as still dormant (see 24C label).  To be effective on blueberries, sprays will probably have to be applied by late January/early February, depending upon variety.

During the past ten years, it has never been necessary to apply Dormex to extremely low chilling varieties such as FlaKing (400 to 450 chill hour requirement).  However, in extreme southern counties, Dormex may prove beneficial on low chillers in the 400 to 500 hour chilling class, which includes Texstar.  To apply while buds are still dormant on these very low chillers will most likely require late January/early February applications.  If fruit buds are already swelling on these ultra low chillers, don't use Dormex (fruit buds will be over-thinned).

We will remind growers in southern and central counties when enough chilling has been received to begin applying Dormex for each chilling class (650, 750, 850, etc.).  However, this doesn't mean the grower should immediately begin Dormex sprays.  As long as cool to cold temperatures are forecast to continue (beyond this initial application window), waiting to apply Dormex at a higher level of chilling accumulation will help reduce the possibility of advancing the date of flowering.  However, waiting too late could result in over-thinning of fruit buds.

Growers should consult the table below in the option on this home page entitled "Action Program for Dormex Application on Peaches" for determining if enough chilling has been received to initiate Dormex sprays.  In addition, they should cut fruit buds every other day to ascertain if buds are still dormant or if they have advanced to a stage of greenish-yellow development, (which means excessive bud thinning could occur from 1% Dormex sprays).  A razor knife may be used to cut fruit buds lengthwise beginning at the base of the bud, cutting toward the tip to examine pollen development.  A 10x magnifying glass is quite adequate.  Pollen in dormant fruit buds which are still receiving chilling are very small translucent (light) green to whitish-green somewhat circular structures that surround the rod-like light-greenish pistil (female part of flower).  Refer to the graphics section of this home page for further details and viewing of fruit buds.

Once the small pollen grains start changing from light-green to a greenish-yellow color, fruit buds are very sensitive to Dormex and over-thinning commonly occurs.  This stage of color development of pollen begins when chilling is complete for the winter (only 60% or more of chilling requirement is necessary for this development to begin) and before full swell.  At full bud swell/1st green, pollen grains are enlarged, golden in color and nearly mature.