The outlook for glyphosate-tolerant lettuce is promising, but development is on hold, pending consumer acceptance of genetically-modified crops, according to Kai Umeda, University of Arizona Cooperative Extension agent at Phoenix.
Although he had no trials on the practice in 2002, he said his trials in 2000 and 2001 at Yuma showed season-long weed control of Roundup with the Roundup-Ready lettuce cultivar, Raider, was superior to the conventional practice of using the herbicides Kerb and Prefar in pre-emergence soil applications.
Hand hoeing costs, he said, were minimal for the Roundup-Ready plots treated at the two-leaf and four-leaf stages. “Optimum timing was between the two-leaf and six-leaf stages, or about the equivalent of typical thinning time.”
Treatments applied at the two- or four-leaf stages required the least amount of hand weeding and yielded the highest fresh weights. Treatment at those times gave nearly total control of major weed pests, common purslane, nettleleaf goosefoot, cheeseweed, and sprangletop. Applications at the six- and eight-leaf stages were less successful on common purslane.
The project, however, is presently on hold because consumers and restaurant operators have not yet accepted the concept of genetically-modified crops. “If this were approved, it would make weed control in a lot of our crops much simpler,” he said.
Umeda spoke at Yuma during the recent Desert Crops Workshop sponsored by Western Farm Press, University of Arizona Cooperative Extension, and University of California Cooperative Extension.
Also on the program was James Walworth, UA soils specialist at Yuma, who said his studies of broccoli fertilization through buried drip systems showed frequency of nitrogen treatments was not an issue, provided adequate amounts of the nutrient were applied.
His trials on medium-textured soil at the Maricopa Ag Center used split applications of nitrogen at intervals ranging from daily to monthly, applied through the drip lines. Rates of nitrogen ranged from a low of 178 pounds to a high of 268 pounds.
“There was no difference between the intervals of treatments, and frequency of fertilizer application did not matter,” Walworth said.
However, he added, some differences might be expected on coarser-textured soils, where more irrigation water is lost.
Workshop speaker Barron Orr, UA Cooperative Extension geospatial specialist at Tucson, said only about five percent of the nation's farmers are adopting geospatial technology, which includes satellite imagery, computerized weathercast maps, and global positioning systems.
Crops such as soybeans, wheat, and corn are using it the most because research on the technology was done first on them.
Although not yet universal, the technology is increasingly a part of the equipment farmers purchase, and his aim to bridge the considerable gap between the technology and everyday farm practices.
One purpose of his work is explaining the fact that the technology can perceive differences in vegetation that human eyesight cannot. Infrared satellite imagery, for example, can detect crop conditions using the light values of the electro-magnetic spectrum, of which only a small portion is visible to the human eye.
“Just because our eyes can't see something doesn't mean we can't take advantage of this technology. We can use it to generate maps for vegetation density, water deficit, or crop stress.”
He noted the smaller or finer the spatial resolution of the technology, the more expensive the technology.