TURN DOWN THE VOLUME
Low-volume sprayer’s nozzles emit an electrostatically charged mist.
Low-volume pesticide spraying in citrus and other fruit offers numerous advantages, field use shows
BY ERIC MCMULLIN
Farmers can use all the win-win situations they can get. So there’s no reason not to at least consider low-volume spraying in fruit.
The practice doesn’t require a wholesale shift in thinking (it’s still a sprayer you’re using, after all); it saves on chemical, fuel, labor and equipment; and insect and disease control is as good or better than that achieved with many dilute sprays.
The most serious concern is red scale in citrus. Even there, a number of practitioners of low-volume spraying say they’re getting solid control.
Dennis Johnston manages about 750 acres for Kransig Corp. The acreage is split two-thirds to tree crops and one-third to field crops, and is located near Strathmore. Johnston purchased a low-volume sprayer eight years ago and uses it in prunes, olives and oranges.
In prunes and olives, he generally uses 35 to 50 gallons per acre. In oranges, he ranges between 50 and 100 gallons. He still has his dilute sprayer and uses it for about a quarter of his spraying.
"In the deciduous trees, the canopy is easier to penetrate. In citrus, there’s so much foliage that a lot of farmers worry that they can’t get coverage. I guess we worry about that a little ourselves," he explains.
In the prunes, Johnston goes exclusively low-volume.
In olives, "I do all my spraying with the low-volume sprayer except my black scale control. Then I use both rigs. That’s partially to get the job done in a timely manner, and partially peace of mind. If I have an orchard that’s a little dirtier than the others, I’ll use the dilute sprayer there. Though I don’t see a great difference in control, I see enough that I figure I might as well take advantage of my dilute sprayer there."
In oranges, "I do all my spraying with the low-volume sprayer except the gibberillic acid and red scale sprays. There I use the dilute sprayer exclusively. For red scale, it’s just peace of mind. You like to see all that volume going out."
Johnston doesn’t have a heavy scale problem — "I usually need to spray every other year," he says — but what if he bought the low-volume sprayer, then found it wasn’t adequate for a heavier infestation of scale?
"I’d use it for everything but scale, then have the scale job done by a custom sprayer."
Jack Dibble, UC-Extension entomologist at the Kearney Ag Center, has spent the last five years researching low-volume spraying in both deciduous and citrus crops. He says the majority of deciduous crop growers now use low-volume, and a growing number of citrus growers do, too. The advantages are numerous:
"You can spray more acres with one tank, so you mix and load about a fifth or tenth as often depending on tank size and the gallons per acre applied. Growers are seeing chemical savings of about 25 to 30 percent because there’s no runoff onto the ground. Energy use and labor are cut and there’s no need for a nurse rig. The low-volume sprayer often costs less in the first place, so there can be a capital investment savings. And you’re saving the energy needed to produce the pesticides, many of which are made from hydrocarbons."
Dibble’s recent work was supported by the California Energy Commission. Once the energy savings were apparent, the commission offered low-interest loans to purchase low-volume sprayers. More than a dozen growers, including Johnston, took the commission’s offer, reports Ricardo Amon, lead director of the commission’s Ag Energy Assistance Program.
Johnston confirms the savings. "With high-volume spraying, you have one driver on the spray rig, plus a driver on the nurse rig. You have the tractor’s engine plus the sprayer’s engine, plus the engine on the nurse rig. With low-volume, you have one tractor engine and one driver. That’s three engines to one, and two drivers to one."
Johnston uses a 45-hp tractor with his dilute sprayer and an 80-hp tractor with the pto-driven low-volume sprayer, so the savings aren’t a straight three-to-one. But the ability to go longer without mixing and loading also counts.
In addition, "we’re using less chemical, plus we feel comfortable going with the lower label rates because we’re not seeing any runoff. And we’ve been able to eliminate a pass some years because our control is better."
All in all, "we’ve calculated our savings from everything and we came up with a very conservative estimate of one-third of all our costs," says Johnston. "It wouldn’t surprise me if it’s even higher that that."
Robert Hengst of Woodlake is another recipient of a low-interest loan. He says he’s pleased with the sprayer and pest control is adequate. He uses 100 gallons to the acre in both his plums and his citrus.
For red scale, he starts with aphitis beneficial wasp, and didn’t spray at all this year. He says he hasn’t calculated his fuel savings, but is confident he’s getting them.
Johnston has an air-driven FMC 757 dilute sprayer with a diesel engine, and a 550-gallon Spectrum low-volume sprayer. The Spectrum also features electrostatics, which were part of the field trials but which Dibble isn’t sure are doing all that much.
Electrostatics work by negatively charging water droplets so they’re attracted to the positively charged leaves. "But as you increase gallons from, say, 35 to 100, the droplet size increases and it’s harder for the droplet to hold a charge. We weren’t able to document any significant advantage above 50 gallons to the acre."
Johnston likes the electrostatics. "We’ve tested with dye and a black light to see whether the chemical is getting on the inside as well as the outside of the leaves, and it is. When you go through an orchard and the sun is behind you, you can look back and just see this mist hovering and getting sucked right onto the trees. Maybe that’s just wishful thinking, but other growers say the same thing."
The smaller droplets do introduce one downside: drift potential. "We encourage growers to spray at night and/or when wind speeds outside the orchard are negligible," reports Dibble.
Driving speed is more critical with lower volumes. "Growers tend to want to get through the orchard quicker, but the rule of thumb is: no more than 2.5 mph with high-volume sprayers, and 2 mph with low-volume. Speed of travel is very important," he says.
One final note: Some chemical labels specify the lowest rate you can use and sometimes those are higher than what you’d want with a low-volume, electrostatic sprayer. There are usually alternative chemicals available but it’s important to make sure your chemical label allows a lower rate.