Bill Kreuger, From Olive News, University of California Cooperative Extension Glenn county

2003 Fruit Set Observations and Implications

Many area growers experienced disappointing crop set in 2003. Shotberry (small worthless fruit) production was higher than usual, especially with Manzanillo variety. While the reasons for these observations is not completely clear, trying to understand what happened can be useful as 2004 bloom and fruit set period approaches.

Alternate bearing. Olives are notorious for alternate bearing. In my experience, one of the most reliable predictors of crop is the crop the previous year. Large crops tend to lead to smaller crops the following year. I think alternate bearing was a major factor in the disappointing Sevillano crop. Generally we had two heavy Sevillano crops back to back in 2001 and 2002. Most Sevillano orchards showed a very light bloom in 2003. This potential light crop was predictable from the limited amount of new growth that was present in the trees. The previous heavy crop limited shoot growth and because the flowers are born only on the new shoots, this limited the flowers andp9t.ential crop.

There were some orchards which had what appeared to be adequate bloom, but ended up with light crops with lots of shotberries. Many olive varieties and Manzanillo in particular are only partially self fruitful. What this means is that, while pollen from Manzanillo is capable of setting Manzanillo fruit, this pollen germinates slower and grows slower down the pistil and may not reach the ovary while it is still receptive. Pollen from another compatible variety will germinate and grow faster and therefore can be more effective in setting fruit. This problem is aggravated by unseasonably warm weather during the bloom period because the period of susceptibility will be reduced due to accelerated degeneration of the ovary. Last year in the Orland area, I recorded full bloom in two Manzanillo orchards on May 22nd. Average maximum temperatures for the three day period from May 20 to May 23 were 11 degrees higher than average. Conditions such as these would be expected to emphasize the importance of cross pollination.

In the San Joaquin Valley, the importance of cross pollination to fruit set has been clearly demonstrated and artificial pollination is a common practice in areas where natural cross pollination is limited. In the Sacramento Valley, where Manzanillos are often planted in close proximity to Sevillano and there is presumably a large amount of Sevillano pollen in the air during bloom, demonstrating the benefit of cross pollination has been difficult.

We have often observed higher levels of shotberry fruit in the more isolated orchards which would likely have less exposure to Sevillano pollen. Last year this situation was exaggerated to the point, I believe, crop load was negatively affected.

Wet rainy weather or wind during bloom can also negatively affect fruit set.

In conclusion, most local Manzanillo orchards usually will set adequate crops without artificial pollination, however in isolated orchards or in years which are not conducive to good pollination Manzanillo blocks may benefit from artificial pollination. In the San Joaquin Valley, typically, a total of 100 to 120 grams per acre of pollen from a compatible variety are applied 2 to 4 times during the bloom.