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Remote sensing technology spots aphid-stressed wheat
Bushland, Texas
August 25, 2004

Dr. Mustafa Mirik, assistant research scientist with Texas Agricultural Experiment Station, and a team of collaborators, are looking at plant damage and stress in wheat. Their current work deals with damage caused by aphids. In the future, the team plans to include other stress factors, such as drought and disease.

Using remote sensing technology, Mirik and his team employed hyperspectral and multispectral equipment to help assess insect damage from greater distances. Field scouting alone does not yield such extensive information.

For example, they took multispectral images ranging from near ultraviolet through most the visible light spectrum. The more sensitive hyperspectral equipment also allows the scientists to see much higher wave lengths than visible light.

Dr. Jerry Michels, Experiment Station entomologist and program leader at Bushland said if the observations are sensitive enough, the scope of the damage can be determined accurately. The goal is to help a farmer pinpoint where treatment applications need to go.

"If this work is successful, farmers may be able to save some money and help the environment," Michels said.
Images were taken by both devices before the researchers went into a field. Then the aphids were counted. They gathered data from all sources for comparison and evaluation.

Mirik used both hand-held and aircraft-mounted equipment in the study. The more sensitive hyperspectral unit can be used closeup or remotely but is more expensive. The multispectral equipment was hand-held only.
Research by others has dealt with establishing crop characteristics, such as green canopy health and cover.
"However, to our knowledge, a limited number of those studies were focused on spectral measurement of aphid-damaged wheat in controlled environments at the leaf-level only," Mirik said.

"Little attention was dedicated to aphid feeding damage at canopy levels in field conditions," he said. "This became the focus our research."

The researchers counted insect densities for greenbug and Russian wheat aphids. They gathered needed information in and above stressed and unaffected wheat plots in Texas, Oklahoma and Colorado. Data was generated from the hyperspectral ground spectrometer and a digital camera above the aphid-infested and non-infested wheat. Insect density was measured in quarter square meter ratios for each sample.

"Sometimes at least 30 tillers were cut at ground level and taken to the laboratory where aphids were counted for each plot," Mirik said. Plot sampling was intensive.

Tillers that remained in the plot also were counted so complete estimates of aphid density were possible. At other times, technicians counted all aphids within plots during the early growing season or clipped all plants and counted aphids in the laboratory during the late growing season.

Comparisons were made in healthy and stressed wheat under all conditions. Early results show promise for remote measurement of aphid-induced stress to estimate density and separate injured from healthy wheat.
Future work will collect image data for aphid infestation of agricultural crops not only in field conditions but in controlled environments, Mirik said.

"We will take this research into at least three levels of stress–water, nutrient and aphid in wheat and sorghum in the future. Our goal is developing and validating a spectral aphid stress index for major agricultural crops."

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