The threat of spring frost damage is always a concern for Arizona pistachio farmer Jim Graham, and this year has been no exception.
His operation, Cochise Groves LLC, includes 160 acres of trees at an elevation of 4,300 feet near Cochise, in the southeast corner of the state. On the mornings of April 10-11, about two weeks after the trees began blooming, temperatures dropped to critical levels — at one point registering 27 degrees briefly. His frost control efforts succeeded in protecting all but one part of one orchard.
“We had a little bit of damage, but we won’t know how much until July when the nuts start to fill,” Graham said in late April. “Right now, it looks like a decent crop, but if the frost hurt pollination we could end up with nothing in that area.”
When frost is in the forecast, he leaveshis micro-sprinklers onduring the day to retain as much heat as possible through the night. As the temperature drops closer to the freezing level, he also turns on wind machines, which help protect all but about 35 acres of his orchards.
Two tractors with mounted propane burners start rolling between the rows of trees when temperatures fall to around 33 degrees. The burners are designed to blow heat about 200 feet to either side. “We run a pattern that allows for some overlap and enables us to cover the same spot every 10 minutes,” he says.
Graham farmed 1,300 acres in Iowa for 25 years before joining his in-laws in their pistachio business in 1995. Three years later, he and wife Ruth took over operation of the original 64-acre orchard and began adding to it.
The pistachio trees, most about 30 years old, include the fruit-bearing Kerman cultivarand Peters males for pollinators. In 2010, an on-year, they produced a 4,500-pound crop.
“This year, following those excellent yields, I’m cautiously optimistic” he says. “The trees look pretty decent for an off-year, and if we can get a 1,500-pound crop, I’ll be fairly satisfied. That’s about as much as we could expect. The Kerman is budded primarily on Atlantica rootstock, which seems to exaggerate the alternate bearing cycle.”
In addition to the frost threat, adequate supplies of irrigation water for the trees have been a continuing concern for Graham.
“Since I’ve been growing pistachios here, the weather has been abnormallydry. This past winter and spring have been exceptionally dry — we’ve had no significant rainfall.” As a result, his pumps run much of the time.
This year he started irrigating on the first day of spring. During the first half of the season, he waters each block of trees once a week, as needed, to maintain adequate soil moisture levels. When the pistachio kernels begin to fill in July, he increases water applications. He monitors water usage and the trees’ needs with the University of Arizona’s Arizona Meteorological Network (AZMET) of automated weather stations to track evapotranspiration rates.
Also, in a program offered by the local Natural Resources Conservation district office, he’s been experimenting with a single Sentek Technologies soil moisture probe in one block. It’s an expensive system, he says, but he’s pleased with the information it has been providing.
“The graphs show pretty clearly how soil moisture increases with each irrigation and then tails off,” Graham says. “It gives us a better handle on when we should start our next irrigation.”
In the past few years, he’s had a surge of septoria leaf spot in his orchards. The fungal disease is triggered by the hot, humid conditions that coincide with monsoon rains that typically start around the first of July. The disease can cause untreated trees to defoliate in the autumn, as much as two months prematurely. Traditionally, growers in his area have used copper hydroxide to control the disease, but Graham has been trying other fungicides.
“Although we’re still using copper hydroxide for some treatments, we’re trying some new chemistries in order to broaden the control spectrum. Kocide has been quite effective, but it has to be reapplied after nearly every rain, and in an active monsoon season, that can mean a lot of spraying.”
As an alternative, he has also been using strobilurin products and is cooperating in experimental trials for new products, not yet labeled, that have shown promise in his orchards.
Controlling weeds with contact herbicides has often been a struggle, Graham says. This year, for the first time, he tried a preemergence approach. So far, I’m pretty excited about it,” he says. “It has done a really spectacular job.”