Citrus researcher Glenn Wright of the Yuma Mesa Agricultural Center revealed his trial results during the recent Desert Crops Workshop at Yuma.

His and others’ reports were the first citrus research discussed at the annual event, jointly sponsored by Western Farm Press, University of Arizona Cooperative Extension, and University of California Cooperative Extension.

Noting that lemons are Arizona’s most important citrus crop, Wright said the main traits sought in his variety trials over the last eight to nine years were high yields, early-season sizing, and economic bearing early in the tree’s life.

Cavers Lisbon, a variety long known in California’s Central Valley, yielded the equivalent of more than 500 boxes to the acre in Wright’s trials. It also showed good early-season sizing (about 60 percent for first harvest) and good vigor.

"The Cavers has performed so well over several years that I would not hesitate to recommend it for trial plantings," he said.

Parallel in yield

The vigorous Spanish variety, Limonero Fino 49, has paralleled Cavers in yield, and in 2001 posted equivalent yields of 600 boxes per acre. It typically also has considerable first-harvest fruit, although its fruit tend to form toward the outside of the tree and are subject to some sunburn.

Both varieties, Wright said, have consistently outperformed the standard, Limoneira 8A, as well as other Lisbon and Eureka varieties, in his trials.

The trials also studied mandarins, with emphasis on rating for precocity, high yields, lack of seeds, and lack of granulation. Wright found the Fallglo variety had brilliant color, excellent size, and ease of peeling but heavy seeding, so he hopes to try the Fallglo Seedless variety.

The W. Murcott Afourer was easy to peel and did not granulate, but tends to have a later harvest date than others.

Early in 2003 he expects to add to the trials the four-variety TDE series, No. 1 through No. 4. They are the triploid crosses of Temple tangor, Dancy mandarin, and Encore mandarin released by the University of California and have few seeds. He also plans to set out Delite trees from California the following fall.

Mites study

Reporting on his citrus study on mites in 2002, David Kerns, IPM specialist at the Yuma Agricultural Center, said growers should scout for the Yuma spider mite because it may be as important a pest as the more familiar flat mite. Both have been a problem for Arizona growers in recent seasons.

"Mites can cause significant damage and in the past we have overlooked this. We need to scout for them throughout the summer, at least through July."

Kerns’ evaluations of several miticides showed that all worked well on both species for about two weeks after application and Danitol and Kelthane gave the best control.

The Yuma spider mite, identified in the area in 1934, has a wide host range, although it prefers lemon. It feeds on undersides of leaves and occurs most often along edges of groves, where it seeks dusty foliage adjacent to roads.

"But in the last couple of years," he added, "we also found it throughout groves and not necessarily in dusty conditions."

Signs of it include webbing on the underside of leaves and stippling on the top side. A severe infestation can defoliate young trees, and high numbers also cause scabbing and pitting of fruit.

The extremely small, flat mite, known in the area since 1942, does not leave webbing and prefers the fruit, causing severe brownish scarring. It often selects thrips damage sites. The damage can be mistaken for wind or rub damage.

Weed Seeker

Rounding out the citrus research reports was

William B. McCloskey, UA weed science specialist, who obtained good pre- and post-emergence weed control and economy with a Weed Seeker mounted on a small four-wheel-drive, all-terrain vehicle.

He said he turned to the sensor-controlled equipment because they were said to have significantly lower labor and chemical costs than either broadcasting or spot spraying. The devices detect the green color of weeds and trigger the spray on individual weeds.

Compared to conventional technology, the post-emergence application used about one-third of the herbicide, while a pre-emergence and post-emergence strategy saved about two-thirds in material. The equipment also saved on labor costs for filling and mixing because more area was covered per tank load.

In the conventional spray boom check application, 20 gallons of solution was needed for each acre, while the Weed Seeker unit needed only 16 gallons.

Expressing the economy in another way, McCloskey said he found that the sensor unit actually sprayed only half as much area as the conventional rig.

At first he used the sensors on a boom mounted on a tractor, but its length proved to be difficult to maneuver around trees. The small 4WD unit, however, allowed much improved coverage next to trees.

He said he plans future trials to learn how the savings balance against the costs of the sensor equipment.