This was no simple walk down memory lane when Ted DeJong, a retired University of California (UC) pomologist, delivered presentations at a stone fruit physiology event held at the Kearney Agricultural Center in Parlier where he worked for 36 years.

It included a look at the future, including the decline in tree fruit acreage; the growth in nut acreage and what the trees have in common; the wisdom of flooding orchards; ways to create future stone fruit orchards where labor costs can be cut by controlling tree size, more efficient water and nutrient delivery with sub-surface drip system; plus cautionary comments on nitrogen use.

DeJong, Emeritus professor and Cooperative Extension specialist with the UC Davis Plant Sciences Department, opened his talk by saying it was a look at “what did I do for 36 years and what’s new.” He acknowledged the help of research colleagues over the decades, including Kevin Day, David Ramming, Scott Johnson, Jim Doyle, and Bob Beede.

He recalled a time when a tree fruit meeting at the Kearney Center would draw between 100 and 300 people. This meeting drew fewer than 100, some more interested in nut crops at a time when stone fruit acreage in the Valley is down by a third compared to several decades ago.

DeJong pointed out similarities in the physiology of nut and tree fruit crops plus the differences, including the need to thin tree fruit to maximize fruit size while the aim with nut crops is for maximum yield.

During a field stop, workshop participants saw what was billed as the “Peach and Nectarine Orchard of the Future,” a plot where size-controlling rootstocks were planted.

Kevin Day, UC tree fruit advisor in Tulare County, said the trees - no more than eight feet tall - were part of a “ladderless” pedestrian orchard. The trees were planted on Controller rootstock which has 90 percent of the vigor of Nemaguard, the standard rootstock used in the California fresh fruit industry.

“When you jam the trees closer together, dwarfing becomes more dwarfing,” he said. “It’s more like 20 percent rather than 10 percent.”

Most conventional peach or nectarine trees are 12-to-13 feet high. Day said the labor component of fresh fruit production is the greatest production cost. Ladders can add anywhere from 25 to 45 percent to costs, and with labor costs rising in the state this has become an even greater issue.

According to Day, yields in the plot have been “superior to 12-foot tall Nemaguard trees,” and fruit size has been better. The experimental plot is pruned without ladders and thinned with ladders. The first pick is done with ladders; everything else is done without ladders.

Becky Phene, staff research associate with UC Davis, discussed using sub-surface drip to irrigate and fertigate most trees in the experimental plot. Those on Nemaguard rootstock are irrigated with microsprinklers.

The idea is to use high frequency irrigations, she said, and only apply what’s needed to avoid applying more water than the soil can hold. Claude Phene, an irrigation and soil physics consultant from Clovis, said the approach minimizes the amount of nitrates going out of the root zone and into the ground water.

In one of his talks, DeJong warned fruit growers of impending restrictions on nitrogen applications – the concept that growers would need to apply only as much nitrogen as they remove in the harvest of a crop. He believes this could greatly cripple tree fruit growers over time.

Claude Phene, a pioneer in sub-surface drip, said if water is applied properly it should not leach nitrates into the groundwater.

Phene, retired irrigation scientist with the U.S. Department of Agriculture, also elaborated on a point DeJong made about the Almond Board of California “spending hundreds of thousands of dollars to flood orchards to drive water to the water table.”

It’s DeJong’s belief that “more trees die from excess water due to poor irrigation than to drought.”

Phene and DeJong made the case that this can result in damage – if not death – to tree roots deprived of oxygen by the water. Phene said tree roots can die within three minutes under water.

“With flooding the orchards, they’re killing the roots,” he said, adding that the flooding adds to leaching of nitrates. He drew an analogy to a person keeping their head under water for three or four minutes.

Phene also referred to DeJong’s explanation of photosynthesis as “a compromise” in which tree leaves trees take in carbon dioxide and lose water. He said more carbon dioxide can be delivered in greenhouses, and predicted that “if demand on water keeps on increasing you’ll see a million acres of greenhouses in this Valley. It will replace open agriculture, and you’ll get the same yield.”

DeJong and others have developed a digital model called L-Peach that can be tweaked to show response to environmental and horticultural management practices. It can help determine how to minimize excessive tree growth to reduce labor costs and direct more carbohydrates and nutrients to fruit production. They also have come up with a L-Almond model.

The models help predict harvest dates, which is especially important to tree nut growers who must line up harvesting equipment ahead of time.

DeJong said it is important for tree fruit growers to thin tree fruit early in years with high spring temperatures and heavy fruit set.

“Potential fruit growth lost early in the season due to late thinning cannot be made up by thinning harder late in the season,’ he said.

DeJong added that global warming is likely “to have substantial effects on developmental processes” in tree fruit, some of them negative.