LACK OF CHILL: WHERE DO WE GO FROM HERE?

Georgia Researchers and Specialists Provide Recommendations for What’s Happening Now in the Orchard

This is definitely going to be remembered as one of the most difficult years in peach production in the Southeastern U.S.  Lack of chill and a late freeze have done their part.  Now, it is time to decide what to do with the trees that are still not coming along as they should.

At present, we can more than likely categorize trees into three groups: 1) acting normal, 2) blooming slowly and leaves somewhat coming in, and finally 3) trees that are still dormant (no leaves and no bloom).  What follows is a potential plan that could be used for management for the two latter groups.  However, remember that we are new to this situation as well and the following recommendations are made based on the best of our knowledge and information collected from different sources.

TREES WITH BLOOMS and SOME/FEW LEAVES

These trees are still having a hard time with the lack of chill.  Blooms are slowly progressing, which is likely going to extend the harvest period as well.  Now, one question for sure on your minds is: are they going to set?  In a late bloom during high temperatures, we would expect to encounter issues with setting, aborted embryos, and problems with shape and quality.  We should be able to tell after one or two weeks if the fruit present is actually swelling, then we can start cutting some fruit to see if the embryos are normal.  This will allow you to decide if you have a crop or not in that block that is worth carrying through the season.  Now, how should we plan to deal with the presence of few leaves or lack of them?  In these varieties, you are likely seeing leaf break and progression around the winter pruning cut points where suckers were located.  These trees are most likely going to progress, but it would seem prudent to provide some help as well.  A foliar application of ammonium nitrate or any nitrogen source could provide trees with some rapidly available nutrients, with urea probably being the least expensive and calcium nitrate being the fastest acting.  Also, remember we are, unfortunately, in a drought as well.  Lack of water has been shown to limit tree growth, but water is also required for all physiological processes in a tree.  Watering trees to supplement available soil moisture is recommended.  Tree requirements of water at this point are still minimal, but it would be good to put out enough water to keep the soil moist.  This will be different depending on the type of irrigation system, i.e. drip vs. overhead.  We would recommend at least 1 gallon of water per tree per day for small trees (i.e. one- and two-year-old) and 5 gallons of water per day for larger trees (three-year-old and over).  This will be recommended to start the season for at least two to four weeks.  Afterwards, it will be recommended to continue with irrigation following your general procedures.

In a study looking at winter damage in peach trees, we compared four treatments to promote vegetative bud break: 1) use of a plant growth regulator (Maxcel – 6-Benzyladenine), 2) a foliar fertilizer (low biuret urea), 3) a combination of urea plus Maxcel, and 4) a control (no treatment).  It was found that the control had similar volume canopy as all the other treatments.  We recommend for trees with blooms with some/few leaves to wait until you can figure out what vegetative buds broke and then come back and do selective pruning of branches and limbs that don’t have any active shoot growth.  We concluded that the use of plant growth regulators such as Maxcel and Progibb will not really produce much benefit.  These trees need to be maintained for the next few months in the same way that trees with leaves and fruit are normally managed.

TREES THAT ARE STILL DORMANT

Trees that have not shown any bud break (either floral or vegetative) by now are not going to come out or they will come out very late.  It is time to assess the different varieties that are in this category.  In a study by Dozier et al. (1990), Dormex was applied approximately six weeks after normal budbreak in 17 varieties with insufficient chill in Fairhope, AL.  This spray was done on April 13.  The trial compared Dormex at one percent and two percent vs. an unsprayed control.  It was reported that there was a better response overall for the two-percent-Dormex application.

It is recommended that Dormex be sprayed at two percent on those varieties that have not come out.  We will be evaluating the use of higher rates, but at this time this is the best information that we have.  As you can see, the applications were made about a week earlier than the time this article was submitted for publication, so it would be advisable to proceed immediately in the varieties that need it.  Remember that there are temperature restrictions when applying Dormex, so be sure to follow label instructions.

Trees should start responding about 21 days after application as described in the paper.  Please consider once the leaves are out to make a foliar application of ammonium nitrate that will provide trees with some readily available nutrients.  Also, remember we are in a drought.  It would be prudent to provide some supplemental moisture to minimize stress on these struggling trees.  Finally, as before, we recommend waiting until you can figure out what vegetative buds broke and come back and do selective pruning of branches and limbs that don’t have any vegetative buds.  This will allow you to recover the plant canopy as soon as possible.

FINAL REMARKS

Most of you have done a first fertilizer application in March.  Varieties and plots that potentially have a crop will need a complete fertilization (as it would be done in a regular year).  However, this scheme will not be good for trees without fruit.  Saving as much unnecessary investment as possible will be important, but also avoid overfertilizing trees without fruit.  This may cause problems of excess of Nitrogen, mostly, next year, with more pruning, shading, susceptibility to pests, etc.  More aggressive tissue sampling might be in order to identify nutritional deficiencies in the plants as needed.

Similarly, it is important to mention that some of the trees that are having issues in leafing out and are coming slowly, may have also issues of sunscald.  It will be recommended to paint at least the tops of their scaffold limbs (and perhaps the S and SW sides of the trunks).  

Finally, if you decide to go with the route of using Dormex to improve vegetative bud break, please remember about the importance of applying when current temperatures are between 50 to 75° F.  This means that the application window is very limited in the coming weeks.

 

Reference:

Dozier, W.A., et al., 1990.  Hydrogen Cyanamide induces budbreak of peaches and nectarines following inadequate chilling.  HortScience 25(12):1573-1575.

CREDITS

by DARIO CHAVEZ, assistant professor and peach research and extension specialist, Department of Horticulture, University of Georgia, Griffin, GA, in collaboration with TOM BECKMAN, JUAN CARLOS MELGAR, FRANK FUNDERBURK, JEFF COOK, DAVE LOCKWOOD, GREG REIGHARD, and GREG HENDERSON.