LUBBOCK — Aphids coming to feast on cotton plants on the High Plains this season may find the humidity in this normally dry climate truly unbearable.
Scientists are hoping that a fine mist from a sprinkler system will help fend off damaging early season insects at the Texas Agricultural Experiment Station at Halfway.
If all goes as planned, the aphids, or plant lice, won’t realize until it’s too late that the tiny water droplets contain fungi that are natural aphid enemies.
“Aphids are very persistent and develop resistance to pesticides very quickly,” said Dr. Robert Lascano, an Experiment Station soil physicist who specializes in biological modeling. He said scientists have been searching for environmentally sound non-chemical methods of controlling aphids more effectively.
Lascano joined with entomologists Drs. Don Rummel and Tom Archer and irrigation engineer Dr. Bill Lyle to begin a two-year study to find whether the environment around a crop can be altered with an irrigation system to assist fungi in controlling aphids on the High Plains.
Several types of aphids may feed on cotton plants from emergence of the first leaves to the time the bolls open. Heavy infestation can harm the plant to the point that fibers don’t develop properly. Plus, honeydew excreted by aphids can drop on the fibers of open bolls. A black, sooty fungus sometimes develops on the honeydew deposits, and the fiber from such fields is stained, sticky and lower quality, resulting in difficult harvest, ginning and yarn spinning.
Presently, farmers hope for unfavorable weather, predators or parasites to control aphids. But during serious outbreaks when growers can’t wait for unpredictable natural occurrences for control, pesticides are used to kill the insects.
“Since about the mid-1970s, when we first began having aphids on the High Plains, at least 40 percent to 50 percent of the time they developed to damaging levels,” said Rummel. “Some of those years were created by insecticides.”
Rummel explained that in previous years pesticide applications on aphids were inexpensive and effective, so farmers routinely sprayed even if an economic infestation was not present. As a result, aphids began to develop a resistance to the chemicals to the point that more and more insecticide was needed to kill the bugs.
In 1991, aphids were deemed the worst cotton pest of the year across the United States, Rummel said. Researchers at the U.S. Department of Agriculture’s Agricultural Research Service in Weslaco began experimenting with various fungi that might attack aphids. He said aphids become ill when they come in contact with certain fungi “like athlete’s foot on a human.” The cellular tissue is destroyed and the insect is desiccated.
“The problem is, the fungus needs 3-4 hours of high humidity to sporulate (reproduce), and that doesn’t happen on the dry High Plains,” Lascano said. Unless the fungus can thrive on the High Plains during the cotton season, use of the aphid’s natural enemy can not be considered.
Rather than give up the idea of natural control, the team decided to try manipulating the favored fungus environment using the Low-Energy Precision Application sprinkler irrigation system developed by Lyle.
Rummel said during the first year of the study, the team will see if a humid condition can be created by the irrigation to enable the fungus to grow. In the second year, he said, the team will consider the rate and number of applications needed to achieve effective control.
If the method is successful, a commercial fungi could be developed for farmers to use in conjunction with the necessary humidity from the LEPA irrigation system, Rummel said.
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