Variable rate application controls cotton nematodes, reduces cost

EDITOR's NOTE: The following article was compiled by Roy Roberson, Farm Press Editorial Staff and Tom Lollis, Extension Editor at Clemson University.

For Springfield, S.C., grower Richard Phillips going high tech in his farming operation is nothing new. An engineer by training, he spent two earlier careers on the cutting edge of communication technology.

Even for Phillips, who farms over 1,200 acres of cotton, corn and hay crops near Springfield, S.C., using electricity conductivity of the soil as a basis for rate of nematicides and variable rate applicators to apply these materials was a leap of faith.

“When Will Henderson and Ahmad Khalilian (Clemson researchers) came to me to talk about using variable rate application for nematicides, I was a little skeptical. Once I understood the technology and saw the economic and environmental savings, it became a part of my operation,” he says.

The variable rate nematicide application system was developed by Clemson University scientists, working at the Edisto Research and Education Center in Blackville, S.C. This system enables farmers to apply fewer chemicals to control nematodes in cotton, save money and protect water quality.

Clemson researchers Ahmad Khalilian, an ag engineer, heads the project. Will Henderson, a precision agriculture specialist; John Mueller, a plant pathologist and technician Richard Hallman make up the Edisto Research team, who have implemented the system on three South Carolina farms. Young Han, an agricultural engineer, and Stephen Klaine and Elizabeth Carraway, environmental toxicologists make up the Clemson research team.

The site-specific nematicide placement (SNP) project is a two-year cooperative effort with the University of Arkansas, which will also place similar systems on three farms in that state, according to project director Khalilian. His counterpart, Terry Kirkpatrick, who heads the Arkansas project, reports similar on-farm success with the nematicide application system.

Phillips was the first South Carolina farmer to have eight-row planting equipment modified by the precision agriculture team at the Edisto research facility. “A year and a half ago I bought GPS equipment for spreading fertilizer and lime,” said Phillips. “Clemson then contacted me and asked if I wanted to get into a high technology project for variable rate nematicide application in cotton. I was very interested, because high-tech is where you save money.”

Phillips has traditionally applied a straight rate of 7 pounds per acre of Temik to his 750 acres of cotton. Using his standard application rate, he would have spent approximately $2,100 for nematicides on the 100-acre field where which the system is being used.

Using the variable rate nematicide application program, he will cut his nematicide bill by at least 25 percent, maybe more, using new Gandy nematicide hoppers adapted for site-specific application.

In a three-year test with another farmer, who used Telone for nematode control, Khalilian says the system allowed the grower to cut his nematode management costs from $36-$39 per acre to $8-$10 per acre. This grower also increased cotton yields by an average of five percent per acre. Even on fields where Temik improved yields by controlling thrips and other early season insects, the system cut nematicide costs by 34 percent.

Most farmers, like Phillips, put a set rate of nematicide on a crop. Too much is an obvious waste of money. However, using too little nematicide can cause as much damage by letting nematodes damage plant roots.

The Clemson researchers divided Phillips' field into three zones. A comparison was made between conventional application of a uniform rate of nematicide and with variable rates based on GPS mapping of soil types as measured with a Veris 3100, which shows the exact location of light, sandy soils and heavier, organic soils by measuring the electricity in the soil.

Nematodes thrive in sandy, lighter soils. Columbia lance nematodes, which are the primary problem on the Phillips farm, have their environmental preferences as the soil varies in texture. The Veris 3100 predicts the level of nematodes in the soil based on its texture.

“Veris seems to very accurately map the soil types that are highly correlated with occurrence of Columbia lance nematodes,” says Mueller. “At least 70 percent of our fields in South Carolina need a nematicide of some sort. The Veris system can take 200 electrical samples per acre.

The best anyone could do before the Veris 3100 is a grid of a half-acre size, according to Mueller. If a grower had a 20-acre field, 40 soil samples would be required to provide an accurate analysis. At $10 each, that adds $400 up front to their nematode program.

Mueller says a Veris soil texture map cost $5 per acre. It's good for a long time and the farmer has multiple uses for it — planning irrigation, fertilizer and lime applications and estimating yield potentials. Veris mapping is already available commercially through Thomas Agri Crop Management in Denmark, S.C., and others will soon offer the service, Mueller says.

Clemson researchers have developed good information on Columbia lance nematodes, and they are developing better information on reniform and root-knot nematodes, which will be essential to a fully mature SNP system for growers, Mueller contends. He expects the system to be used on “quite a few acres” within four or five years.

“In the Phillips field demonstration plots we have a zero rate of nematicide and then 3, 5 and 7 pounds.” The zero rate is our control. It will show us just what effect nematodes are having on yields. We have three soil types in this field — a sandy zone, a medium loamy soil and our heavier zone,” he adds.

Henderson notes the sandier zone received the heaviest rate of Temik since nematodes are more active there. The lowest rates went in the heavier, clay areas.

Six times during the 2006 growing season the Clemson scientists will take 4-foot soil cores from each treatment to send to the Clemson Environmental Toxicology Laboratory for analysis of any Temik movement into groundwater. They will also pull soil samples to monitor nematode populations.

GPS-based yield monitors mounted on cotton pickers at harvest should give a clear correlation between nematicide application rates and yields throughout the field. “The yield monitors will be the true test,” says Phillips. “We can see where nematicides don't work, but not where they do work, so the yield monitors will give us final validation of how much money the system saves us,” he says.

Khalilian said that equipment was also modified for Ray Crapse, who farms in Hampton County, S.C. Clemson is also working with Travis Still of Blackville. Plots have been placed on 30-acre fields of cotton on each farm.

The project is funded by a $322,672 federal Conservation Innovation Grant from the Natural Resource Conservation Service of USDA and matching funds that bring the total cost to $649,490.

The nematicide placement project has been successful enough to convince Phillips to use the Veris 3100-generated maps to drive his irrigation systems.

“High tech is the way to go, and these are some of the first steps we needed to take to go to a more precision farming system,” Phillips says.

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