The program also looked at the following topics:

Mechanization of pruning and harvesting

Louise Ferguson, UC Davis Extension specialist in plant science, said some significant progress has been made in coming up with machine-harvested fruit that is not distinguishable from hand harvested olives.

Ferguson said sensory panels and consumer evaluations were used to judge differences between machine and hand harvested olives.

And machine harvesting does not appear to damage trees greatly, particularly if they are pruned properly. Researchers continue to modify harvesters that either shake the trunks of trees or operate in canopies.

Ferguson said mechanical harvesters must be at 80 percent efficient to equal the cost of hand harvest. At this point, she said, the efficiency rate in shakers is 64 percent; it’s 68 percent for canopy harvesters.

Ferguson said a study showed mechanical pruning did not reduce yield. She said thinning should be done annually.

Olive knot and verticillium management

Elizabeth Fichtner, UC farm advisor for Tulare County, said olive knot can affect fruit flavor. It girdles stems, branches and trunks and results from bacteria that enter through scars in wood, commonly during spring rains.

Fichtner said it can be exacerbated by pruning or harvesting before or during rain, and mechanized harvesting can leave “infection ports.” A post-harvest copper-based treatment in late fall helps combat the disease, but it is developing copper resistance.

Plants coated with a latex polymer have reduced sensitivity to freeze-injury, researchers have found. And several table and oil olive growers in Tulare, Kings, and Fresno Counties are using a latex polymer product for frost protection. Some growers combine the latex polymer with copper in a tank mix to enhance olive knot control.

As for verticillium wilt, sometimes a legacy of old cotton fields, Fichtner said the best way to avoid that soil borne fungus is to not plant olive trees in infected soil.

Use of olive mill waste water for nutrition and management of olive diseases

Ali Rhouma is studying those topics in the African nation of Tunisia at the Laboratory for the Improvement and Protection of Olive Genetic Resources.

He pointed out that Tunisia is either second or third each year in the world export of olives.

Rhouma said research showed waste water from olive oil extraction did not change the Ph levels of soil and that it added organic matter and potassium. He is studying its use on various diseases in olives including root rot, olive knot, leaf spot and branch dieback.

Insect pest management in olives

The olive fruit fly is developing some resistance to the insecticide Spinosad, said Marshall Johnson, an integrated pest management specialist and entomologist with the Kearney Ag Center.

That could mean growers will need to resort to other approaches such as mass trapping, improved orchard sanitation and biocontrols, Johnson said.

Johnson said dense, unpruned canopies are a haven for another pest, black scale. That problem is often compounded by ants that disrupt parasites. And the olive fruit fly may feed on honeydew produced by the scale.

“It’s a double whammy,” Johnson said. “The black scale sucks the vigor from the tree and helps support the olive fruit fly.”

Density in the canopy of olives is also a haven for the olive psyillid, notably in Southern California. But Johnson said that pest is unlikely to thrive in the hotter temperature of the San Joaquin Valley.