Mario Viveros

UCCE Farm Advisor, Kern County

Deciduous Tree Fruits and Nuts

March 2, 2000

A Reduced Almond Bloom for 2000

There is one thing for certain in agriculture. There are no two years alike. We have seen unusual weather phenomenons in each of the past two years. In 1998, the citrus crop was destroyed by a freeze in December and then in the following year. The following year, a rare snow storm blanketed Kern County in late January. This year is already showing its uniqueness. Between November and January, there was only one day of fog and we had cold nights followed by sunny days. This is more like the high desert climate and not like the climate of San Joaquin Valley. The uniqueness of this year's weather will be reflected on this year's almond crop.

This winter season, we accumulated less chilling hours (temperature less than 45°F) than the 1998-1999 season. There were 1036 chilling hours for the 1998-1999 season but only 845 hours for the 1999-2000 season. The chilling hours were better in 1998-1999 season than on the 1999-2000 season. This may be one of the factors that contributed to an outstanding bloom in the 1999 season. The effective bloom of 1999 lasted 17 days while the 2000 bloom may not even last 12 days. This year's almond bloom is not as good as last year's bloom and the Nonpareil bloom is 50 percent of last year's bloom. The pollenizers have better bloom than Nonpareil but they are not as good as last year's bloom. One additional factor that may explain the poor bloom is the heavy Nonpareil crop in 1999. It is a fact that a heavy crop will demand more nutrients and carbohydrates from a tree than a light crop. Most of the nutrients will go to the crop and little will go to shoots and spurs for bloom formation.

In most situations, good bloom leads to good crops. This year the Nonpareil bloom is light and we may not harvest a good crop. However, at this time, there is nothing we can do to improve the bloom in Nonpareil since the flower bud primordia was formed in September and October. This is the time when we stress our trees due to harvest. It is known that water stress can affect the flower bud primordia and therefore decrease the number of flowers for next year's bloom.

There is no reason to stress almond trees at any time during the year since we have appropriate technology to properly irrigate orchards. There is information about the water needs of the tree. We know how much and when to irrigate the orchards. The CIMAS weather stations can provide current information on evapotranspiration (Eto). Manuals and books can provide crop coefficients to determine crop water needs. If ETo information cannot be used, there is instrumentation that can be used to determine tree water stress. The procedure consists of bagging leaves from main branches at noon time. The leaves are allowed to stay in the bags for three hours. The leaves in the bags are then taken from the branches into a pressure bomb where the stem water potential is determined. The stem water potential is a good measurement of water stress levels. Furthermore, there is technology that allows us to continue irrigating our orchards almost to the time of harvest.

There is no reason to create a reduction of bloom due to water stress during flower bud differentiation. We have irrigation knowledge and technology that allow us to have well-watered trees at harvest time. Furthermore, it is critical that water stress be maintained at a minimum during a heavy crop year.