Herbicide resistant weeds, stinkbugs and a host of other pests get a lot of attention for their negative impact on crops in the Southeast. However, year in and year out, much less publicized nematodes are among the most destructive pests of cotton in the region.

CLEMSON RESEARCHER AHMAD Khalilian explains a variable rate nematicide applicator at a recent field day.

In the past 10 years a Clemson University research team, headed by Ag Engineer Ahmad Khalilian, at the Edisto Agricultural Research and Education Center in Blackville, S.C., has developed a variable rate application system that promises to make nematode management more efficient and more affordable.

Khalilian says the system, technically named Site Specific Nematicide Placement System, is ready for commercial deployment and use by farmers.

The first step, he says, is to develop an accurate geo-reference soil texture map. This can be done inexpensively using an electric conductivity meter.

“We can map 750 acres per day using a commercially available electric conductivity meter. If you hire someone to do it for you, and there are consultants available in South Carolina to do this type work, it cost about $5 per acre. The consultant will make the map, divide it into zones and explain what is going on in the soil.

“Another option is to do it yourself. There is software available, and if a grower has that, he can rent the equipment for a dollar an acre, which is probably covered by NRCS programs,” Khalilian says.

Several variables affect the readings this system gives. If soil moisture, salt content or organic matter is high, the system will give high numbers. Soil texture is the critical factor, the Clemson researcher stresses. “If I map here at the Edisto Station today and we get a big rain tomorrow, the readings would change, but the zones would be the same,” he explains.

The readings from the Veris System, which is the electric conductivity meter used at the Blackville research facility, can be dramatic. For example, Khalilian says a nine percent increase in the reading resulted in 57 percent less nematodes on the station.

The next step is to use the readings to divide the soil map into nematode management zones. For example, a 100 acre field may be divided into three zones — high, medium and low nematode population zones.

The third step is to develop precision equipment to utilize the nematode management maps to apply varying rate of nematicides. Making the application system simple enough and affordable enough for farmers to use has been a challenge.

Using the 100 acre field as an example, nematode zones are red, blue and green to signify high, low and medium levels of nematodes. The most likely nematicide options are either granular Temik or liquid Telone.

Using Temik, the Clemson researchers used a Gandy hopper with a gear at the bottom to meter how many granules of the nematicide are applied. One 12-volt variable speed motor is used for a six-row planter. For six to 12-row planters, two motors are used. Each motor costs about $600, Khalilian says.

To control the motor, a simple controller that does one task or more complicated controllers that do multiple tasks can be used — more capability more costs. The simple system used by the Clemson researchers costs about $1,100. It requires inclusion of some way to add a prescription soil map. A computer to do this costs about $300, Khalilian estimates.

A more sophisticated system, like the one currently used by Khalilian’s research team, will eliminate the need for a separate computer and will also incorporate the GPS-guided equipment on a tractor.

The high-end equipment is precise — about one percent error. It can also be used to apply variable rate fertilizer and pesticides. Commercial versions of the system developed by the Clemson researchers are available and being used by a handful of South Carolina growers.

For growers preferring to use Telone, the delivery system is different, but the concept is very similar. The Clemson researchers are working on a switching device that will allow growers to manually switch on the Telone applicator, based on their prescription nematode maps.

“The device isn’t a true variable rate applicator, but it may be the best way to go because of the difficulty in calculating true variable rates for pressurized application of liquid materials,” Khalilian explains.

In one test with a grower in South Carolina, Clemson Precision Ag Specialist Will Henderson says the simple on-off technology proved its value.

“This particular grower was growing about a thousand acres of cotton and was putting Telone under every acre. Using this simple on-off system, combined with nematode sampling and soil electric conductivity sampling, the grower saved about $27,000 worth of Telone in one crop year,” Henderson says.

John Mueller, a long-time plant pathologist and now head of the Edisto Research Center, says, “In our most recent tests, using variable rate application, we varied from zero Telone II to four gallons per acre in the same field. Without variable rate technology, the grower would typically treat for the highest nematode populations using the higher rate of nematicide across the entire field.

“As the nematode pressure goes up in a cotton field, and the cost of pesticides goes up, the need for more precise application becomes increasingly cost effective,” Mueller stresses.

“In one field with variable soils and subsequently variable nematode pressure, we increased yield by 55 pounds of lint per acre. But, we only averaged one half gallon of Telone II per acre, versus the standard uniform treatment of three gallons per acre. So, we saved $25 per acre on Telone II costs, plus another $25 or so on increased lint yield.

“The cost differential is less dramatic in a Temik 15G-treated field, but still we saw a five percent yield increase and 34 percent lower nematicide usage,” Mueller says.

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