Research takes big picture of wheat streak mosaic

05/03/05

AMARILLO Seeing a field of damage confirms a wheat streak mosaic problem exists. Seeing it in fields across multiple counties at one time puts the problem into perspective.

Regionwide perspective is needed to determine how much the disease costs producers and how important it is to begin breeding for resistance. David Jones, Texas Agricultural Experiment Station research associate at Bushland, is using remote sensing to get the big picture.

Wheat streak mosaic, vectored by the wheat curl mite, is the predominant viral disease found in Texas Panhandle wheat, Jones said. Damage can be minimal, but the disease also can wipe out entire fields. With the wet summer last year, Jones is predicting a high occurrence of wheat streak this year.

With the amount of wheat growing in the Panhandle, sampling every field is almost impossible. In past surveys, about 10 fields per county were sampled, but Jones said this doesn't provide an accurately picture.

He is pulling together a combination of satellite imagery, aerial photographs and "ground truth" data (actual information in the field), to more accurately estimate the extent of the disease.

"It's important for farmers to understand how much production loss occurs," Jones said. "It's an economic factor no one has a grasp of yet."

To get that grasp, Jones inoculates wheat streak mosaic into plots of wheat and then takes spectral readings to determine how infected wheat reflects light.

"Once we understand that better, we can look at aerial and satellite imagery and be able to determine specific characteristics that diseased wheat has," Jones said.

With this data, he will be able to conduct a wheat disease survey of the Panhandle using Landsat imagery. Landsat is a satellite orbiting the Earth that is capable of taking images along seven broad spectral bands ranging from visible to near infrared and one band of thermal infrared. Because the satellite passes over the same area every 16 days, Jones can monitor changes throughout the growing season.

He also goes to the fields to collect ground truth data, allowing him to physically identify things in the Landsat images and use as check points.

"Once we get all the data, we hope to accurately assess the amount of wheat streak disease in the Panhandle," he said.

This understanding is necessary, because one of the most extensive management practices in this region can cause wheat streak mosaic to spread.

"Because wheat grown for grazing in this area is planted early, it leads to the spread of the disease," he said. "And wheat producers who plant for both grazing and grain can take a hit on both ends."

In wet years, volunteer wheat grows through the summer and into the fall, providing a host for the wheat curl mite. The mites migrate from the volunteer wheat to the early wheat planted for grazing, he said.

"That's where we have a problem," Jones said. "Later planted wheat would break the cycle between summer hosts and winter wheat emerging in the fall."

No chemical application is available to treat the disease and miticides haven't proven effective, he said. The best control method is to destroy volunteer wheat, so the curl mite can't survive.

The information Jones hopes to get will help justify necessary management practices, such as destroying volunteer wheat. It also can be used to justify research dollars requested to develop wheat streak-resistant varieties.

"This is the best way to look at the whole Panhandle at one time in one season," he said. "We know the problem is out there, we just don't know how big it is."

Source: Eurekalert & others

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