Cotton Links


It’s Time To ‘Zone In’
On Nematodes

By Amanda Huber
Southeast Editor

The days of broadcasting sprays over an entire field are becoming fewer and fewer. Today’s technology allows for a more targeted approach to pest control, and today’s input costs almost necessitate such an approach.

One production factor that can be narrowed down in the field is control of reniform nematodes. Research has shown that management zones can be effectively used to hone in on the problem areas and to direct nematicide applications to places where nematodes are likely to reduce yields.

Richard Davis, a nematologist with the USDA-ARS Crop Protection and Management Research Unit in Tifton, Ga., says the greatest benefit to using management zones is having more accurate information about where in the field nematodes are likely to cause damage and how severe the problems are in each zone.

“That information allows a farmer to decide for each zone whether a nematicide will be beneficial and which nematicide and rate are appropriate,” he says. “Compared to managing a field as a single unit, this reduces costs by putting nematicides only where they are needed, but it actually improves nematode control because it reduces the chances that a significant problem in only part of a field will be overlooked or under treated.”

Soil Texture Most Important

Davis says soil texture is what most affects nematode population levels, and so his approach to creating nematode management zones has been based primarily on soil texture, elevation and slope or changes in elevation.

“Texture is by far the most important factor in virtually all fields, and elevation and slope are important secondary factors,” he says. “For example, root-knot nematodes increase to the highest levels in sandier soils, and reniform nematodes do best in soils with more silt and clay.”

Elevation and slope can affect growth of cotton because those factors affect water drainage, he says.

“Low-lying areas often have greater soil moisture than higher areas,” he says. “The management zones are created so that texture, elevation and slope are fairly uniform within a zone, but those factors will be different among the zones in a field.”

Finding The Zones

Soil texture is determined through the measure of soil electrical conductivity (EC), which Davis says is closely related to soil texture, but is easier, faster and cheaper to measure.

“Soil type does not give you as much precision as soil EC data does; you can have a whole field that is a single soil type, but it can still have a great enough range of textures to have multiple management zones,” he says.

Calvin Perry, University of Georgia agriculture engineer, explains the technology used to create the zones.

“We have been using the Veris 3100 soil EC sensor,” he says. “With a GPS connected to this device, a map can be created for a field showing shallow – zero to 12 inches – and deep – zero to 36 inches – EC values. With GIS software, the EC data can then be manipulated into management zones.”

Davis says there is some subjectivity to the process, and the maps drawn for nematode management zones are different from ones used for fertility, pH or weed management – mainly because those maps are not based on the same factors.

Sample By Zone

The management zones do not tell the producer where nematode levels will be high or even if nematodes are actually in that field, Davis says.

“To find that out, you will still need a random and representative sample for nematodes from each zone,” he says. “Sampling each zone separately increases the chances of identifying areas that have damaging levels and areas that do not.

“The zone maps can be used in a PDA, with GPS, to go out and sample.”

Spray ‘Hot’ Zones

Once the nematode samples are counted, control maps can be created that tell the producer in what zones nematodes are a problem and where to target his sprays.

“This would enhance yield in the ‘hot’ zones by applying the nematicide and save money by not applying where product would not provide much economic benefit,” Perry says.

Davis echoes those comments and says the zone approach should be easy for farmers to use.

“I envision nematode management zones as something that can easily be used by most farmers, but the maps will probably be created mostly by crop consultants and county Extension agents,” he says. “As the software gets easier to use, that may change.”

Current research on reniform nematodes builds on previous work with root-knot nematodes and involves a collaborative effort between the University of Georgia and the USDA-ARS. Cotton Incorporated and the Georgia Cotton Commission have provided support for previous and current research.

Davis says future research includes efforts to determine whether soil texture influences the effectiveness of nematicides; plus research on the interaction of drought stress and nematode damage on cotton yield and fiber quality could influence the recommendations made for the management zones.

Contact Amanda Huber at (352) 486-7006 or ahuber@onegrower.com.

Management Zones Prove To Be Cost-Effective Approach

At a time when saving every penny on inputs is critical, knowing you are only putting product out where it is needed, and not where it is not, is like money in the bank.

Craig Bishop, who produces 2,500 acres of cotton, 1,200 acres of peanuts and 200 acres of corn on his north Florida farm, targets nematodes with zone-specific applications.

Through the use of AutoSteer and yield monitors, data was collected and used to create management zones. Using management zone maps, Bishop pulls soil samples from each zone and also nematode samples.

“We used to do grid sampling, but zone sampling follows the soil much better," he says. “Riding across the field, taking samples, you can start to see those subtle changes in the soil from one zone to the next."

Specific Applications

With a count of how many nematodes are in each management sample, a nematode-prescription map is created. The application map can then be loaded onto a flashcard where it is used by the tractor and applicator to only put product where it is needed.

“I put it in the tractor, turn it on and the tractor practically runs itself," Bishop says. "Instead of broadcasting Telone across all the acres, we are applying it only where nematodes would be a problem. In a 70-acre field, there may not be but about 13 or 14 acres that need treating."

Just treating where a yield-robbing nematode problem is most likely to occur saves time and money.

Benefits Of Zone Management

• Efficient use of insecticide.
• Easier to identify problem areas.
• Other factors identified.
• More accurate information.

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