Chill Hours Update: Watching the Weather and Tallying the Time


PEACH GROWERS from Florida, Georgia, and South and North Carolina are concerned. For a second fall/winter season, 2016-17, climatologists are saying there will be the same warm fall and early winter season the growers had last winter. Orchards need cold weather called chill hours to break dormancy and yield fruit.

“Climatologists are saying we are to have a warmer-than-normal fall and early winter,” says Jeff Cook, University of Georgia Cooperative Extension Taylor/Peach County Ag and Natural Resources Agent. “Last year we were historically warm … too warm. October starts the chill hours counting and we didn’t have any chill hours to amount to anything until January … not a killing frost until January.”

Peaches need chill hours and most varieties in middle Georgia need between 700 and 1,000 hours, Cook points out. Lack of chill hours can cause erratic fruiting and blooming, which can make it hard for farmers to organize their harvest and contributes to decreased yields.

“It depends on where you are as to how the peach crop is,” Cook states. “In middle Georgia, if we get 800 hours, we will be in good shape. Normally, we have 1,100 hours by January 15. We didn’t make it last year, for temperatures were in the mid-70s. I think it definitely had an effect on the fruit quality this year.”

Flooding waters in orchards can be an issue for peaches, but the fields in Georgia have been dry. In fact, no rain was even received in mid- Georgia by recent Hurricane Matthew. “We got breezy days that made the dryness even worse,” Cook recalls. “I don’t know how much rain they received in South and North Carolina, but they were dry and in need of rain so it probably helped.”

“We are in reduction in the number of buds and maybe quality,” Cook observes of the peach crop this year. “Some spots have gone seven to eight weeks now without rain. I would say middle Georgia is part of that exceptional drought, it is so extremely dry.”

“Peach trees set flower buds in summer and normally set too many so we should be okay. Flower bud numbers are not as big a deal as getting the chill hours we need.”

From a growers’ standpoint, they usually don’t start worrying until December, Cook shares. “At this point, the growers are thinking about it, but trying not to worry too much about things we can’t do anything about.”

There is help in creating a manmade chill-hours effect for the peach tree with hydrogen cyanamide (known by brand names as Dormex or Kropmax) that is supposed to boost up to 300 hours of chill to let the tree start breaking dormancy, Cook notes.

The research arm of the extension has been working on ways to make peach trees produce around the chill hours, but haven’t show any effects from it, Cook cites, reminding that researchers like to have multiple years of data — not just one year to share. If this is another light winter, he says that they will at least have another year of research on the problem.

“Right now, we are looking at a warmer winter, but we are still hopeful,” Cook concludes. “If we normally get a couple hundred less chill hours, it would be fine. We just hope we have a winter this year.”