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Frost damage evident in NorCal olives

Generally speaking, olive yields in the Sacramento Valley were lighter last year than the year before. This is in contrast to the San Joaquin Valley, which heralded a large crop last year.

Abundant new growth set the stage for heavy bloom and cropping this year in the Sacramento Valley. At this time, it does not look like this will happen, especially with the Manzanillo variety. Generally, the Manzanillo bloom is sparse to non-existent. Many of the flower buds are not developing. In many cases, the small, undeveloped buds can be seen at the leaf axils. They often appear brown and dry and can be flicked off. The severity of this problem is variable.

There appears to be a geographical gradient from north to south with the problem being more severe in the north and getting somewhat less toward the south. The problem is most severe on Manzanillo. Some damage is being reported on Sevillanos in Tehama County. Most Sevillanos and Missions that I have seen around Orland appear to have a normal bloom. Some Manzanillo orchards in southern Glenn County and further south have been observed developing a reasonable bloom.

What is responsible for this unexpected situation? The frost experienced in February is suspected. From Feb. 15-21, we experienced freezing minimum temperatures with lows around 25 degrees. It was probably colder than this in some parts of Tehama County. Again on March 10, we had freezing minimum temperatures. Normally low temperatures like these would not be expected to cause much damage and nobody I know thought it necessary to frost protect. I have seen freeze damage in the past in December or January which caused defoliation, but did not kill the flower buds. At bloom time, defoliated shoots had blooming flowers which, of course, did not persist to harvest. Evidence to support the hypothesis that this is frost damage includes an orchard in southern Tehama County that has a reasonable bloom only in four rows that were flood irrigated during the freezing conditions. Well water in excess of what was necessary to

run micro-sprinklers in an adjacent almond block was run down these rows. The rest of the orchard was not protected and has limited bloom. In some orchards, a better bloom has been observed in higher areas of the orchard than in the lower areas. This is consistent with the colder heavier air settling in lower areas and has been seen in other years on other crops experiencing frost damage.

Another factor that may have influenced the outcome was the unseasonably warm temperatures experienced for at least a week prior to the frosts. At the time of the frost, crop development on other crops such as almonds was seven to 10 days ahead of normal. It may be that this warm weather increased the physiological activity in the buds and increased their frost susceptibility.

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