Three decades ago, growers never dreamed of harvesting a crop from a third-leaf tree, Edstrom says. Now they're seeing much higher production from third- four- and fifth-leaf trees.
Growers also have followed Edstrom's trials that showed lightly pruned trees yielded significantly more than heavily pruned trees.
But not all of these practices fit every planting situation, and Edstrom says growers may run into increased disease pressure from high vigor trees with dense canopies.
Alternaria, which never was a problem with wider tree spacings, now causes early leaf defoliaton if growers don't stay on top of the disease with fungicides.
Microsprinklers, coupled with a dense canopy, create the perfect microclimate for the fungal disease.
Hull rot, which is associated with higher nitrogen levels, also is becoming more of a problem, Edstrom says.
Mario Viveros, a farm adviser emeritus from Kern County, says hull rot is tied into higher yields, which delay overall crop maturity.
"The more we delay hull split, the more we are opening ourselves up to hull rot," he says. "There are trade-offs that we have to consider with yield increase."
In addition, growers are applying more fungicides because of increased disease pressures, whether from alternatia, hull rot or a host of others.
"I know of a couple of growers who put on seven fungicides sprays—that's getting up there," Edstrom says.
With an average cost of $50 per acre, including materials and application, those growers spent $350 per acre on disease control alone during 2011, he says
"Those high-input production systems produce earlier and have ultra-high yields, but often result in more problems and more costs," Edstrom says. "Especially in high fertility soils, you have to be careful where you apply these practices."