The crop nemesis southern root knot nematode (RKN), Meloidogyne incognita, may have met its match in Arizona crop fields thanks to improved targeted applications of soil fumigants in various soil textures delivered through precision agriculture technology.

Field trials conducted from 2006 to 2010 tabulated information gathered by global positioning systems and variable rate technology, including the electrical conductivity-based Veris 3100 and EM38 sensors for on-the-go soil mapping, plus harvest yield mapping data.

This technology illustrates that nematicide applications can be applied sparingly in some cases while maintaining good nematode control and trimming chemical costs.

The grower cooperator field trials included six studies with the nematicide Telone II applied at pre-plant in cotton and corn in central and southwestern Arizona conducted by University of Arizona (UA) researchers Randy Norton, Tim Hatch, Mike McClure, and Pedro Andrade.

Norton, UA regional extension cotton specialist based in Safford, shared the findings during the 71^st annual Cotton Disease Council meeting at the 2011 Beltwide Cotton Conferences in Atlanta, Ga., in January.

Norton labeled the RKN as the No. 1 nematode species threat in Arizona. The microscopic roundworm damages crops by attacking the young tap and secondary roots which stimulates the production of galls. Galls interfere with the ability of the roots to absorb water and nutrients, and allow other disease-producing organisms to enter the plant.

Arizona hotspots for RKNs include the Coolidge, Casa Grande, Florence, and Buckeye areas in central Arizona and the Bonita area in the Sulphur Springs Valley in southeastern Arizona.

In cotton, the RKN is responsible for a 5 percent lint yield reduction on average across the Cotton Belt, Norton says. Five gallons is the standard Telone II application rate in Arizona to maintain cotton yields in RKN-infected fields.

“The 5 gallon Telone II rate results in tremendous increases in cotton yield per acre,” said Norton, a cotton agronomist. “Heavy RTK infestations without Telone II can result in nearly complete crop loss in highly infested areas.”

Soil texture is directly related to Telone II efficacy. Many Arizona crop fields contain stream and river deposited alluvial soils. A 70-acre field, says Norton, can have five to six soil classifications with high soil texture variability which impact nematode numbers and distribution. The tests reveal that soils dominated by sand have higher RKN numbers. Clay loam-based soil has a low RKN population.

The field trial locations were selected on baseline nematode levels and growers’ experiences. The Veris mapping survey divided the fields into four management zones; Zone 1 with the most sand to Zone 4 with the least sand. A prescription was developed based upon the zones. Zones 1 and 2 were treated with Telone II. Zones 3 and 4 were untreated.

Each trial layout included verification strips (treated and untreated) placed across the field to cross all management zones. Yield data was obtained from a monitor at harvest. Full-length strips across all zones were evaluated along with the yield response within each zone (Telone treated and untreated).

“Observational data suggests that the entire field does not always require a nematicide application,” Norton said. “The ability to target and apply a nematicide to specific areas of a field predicted to have a high potential for crop damage while avoiding application on areas of the field with a low potential for crop damage allows the grower to greatly enhance the efficiency of nematode control thereby improving profitability and reducing the amount of nematicide released into the environment.”  

Two-trial focus

Norton focused on two particular trials in his presentation. The 2009 corn trial in Bonita with farm cooperator Doug Dunlap was conducted on a 120-acre center pivot field with high nematode pressure and soil variability.

Preseason nematode estimates determined by 250cc soil samples included: Zone 1 – 400 RKN, Zone 2 – 240 RKN, Zone 3 – 250 RKN, and Zone 4 – 18 RKN. Telone II application rates were either zero or 5 gallons per acre (GPA). Half of the crop circle (60 acres) was treated with 5 GPA and the other half with no nematicide.

“An analysis of the yield and Veris maps indicate the half treated with Telone had a significant yield response – up to 35 more bushels of corn per acre in the Zone 1 areas,” Norton said. “In Zone 1 areas left without Telone there was a significant reduction in yield.”  The response to Telone II applications in Zones 3 and 4 was minimal.

In the 2010 cotton trial in Buckeye at H-4 Farms operated by the Heiden family, the field featured a high nematode history and a proven response to 5 GPA Telone II applications. The goal was to utilize soil texture differences to reduce but not eliminate the Telone II application in finer soil texture areas.

The standard rate of 5 GPA was used but 3 GPA was applied in finer textured soils. Nematode densities were Zone 1 – 100 RKN, Zone 2 – 75 RKN, Zone 3 – 95 RKN, and Zone 4 – 60 RKN.

Response in lint yield to Telone II application in Buckeye was positive in all four soil texture zones for both the 3 and 5 GPA rates.  However, the response dropped significantly in Zone 4 and was slightly over the breakeven point considering all costs and returns. 

Research results on the six trials demonstrated the ability to maximize return on investment (ROI) with variable applications of Telone II by targeting the coarsest texture soils of a given field.

Norton’s ROI figures are based on 75 cent per pound cotton and $70 per acre for a 5 GPA Telone II application.

The Coolidge trial showed a very strong uptick in cotton yield, a more than 120 percent increase in lint yield with an over $400 per acre ROI in Zone 1. Three years of trials in Safford generated a range of $30 per acre to $150 per acre ROI in the sandiest regions of the field (Zone 1).

The Bonita corn trial brought nearly $120 per acre ROI in Zone 1. The Buckeye trial with the variable nematicide applications returned $200 per acre for the 5 GPA and $120 per acre ROI for the three GPA in Zone 1. The return on investment dropped off significantly in the finer soil texture zone (Zone 4) at all locations. In the highly variable soil textured soils of the Safford Valley, negative ROIs were experienced in Zones 3 and 4.

In summary, Norton says consistent yield increases were achieved with Telone II under heavy nematode populations. Veris soil surveys consistently predicted higher yield responses and maximized ROI, especially in Zones 1 and 2.

Trials will continue this year in Bonita, Safford, and Buckeye to further study field areas with low soil texture variability and conduct more detailed sampling with Veris surveys.

For more information, contact Norton at (928) 428-2432 or [email protected].

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