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Increasing Almond Set: Several Factors Up the Odds

By Joe Traynor

With the disappointing 1995 almond crop now history, pollination, or lack thereof, is receiving the brunt of the blame. It is easy to see why, as most growers remember the ’95 blooming season as a rainy one.

There were, however, a number of excellent rops in 1995 – 1 ton of meats or better per acre. How does one explain these excellent crops? A close look at individual orchards that had good crops in 1995 shows three constant recurring factors that all had in common: 1) Strong bee hives; 2) Young trees (or trees that had not totally filled in between rows, i.e. open orchards) and 3) Retention of leaves during September and October, 1994.

These 3 factors are discussed separately below:

Strong Hives

In spite of the marginal conditions during the 1995 bloom, there were enough good days, or enough good hours on some days, to get the pollination job done – but only if strong hives were present.

During the recent drought years, hive strength was not as important as it was in 1995 since there was ample time for all hives, weak and strong, to cover the bloom. Weather conditions in 1995 gave strong hives the opportunity to shine.

It takes far less time for bees to pollinate an almond than might be imagined. With a compressed bloom, a good crop can be set in a few hours of reasonably good weather during one day. Ample bee populations, however, are necessary to do the pollination job in such a short period of time. Growers that didn’t have strong hives in 1995 simply didn’t have the bee numbers necessary to get the job done.

Young Trees

We’ve heard it in the past years, and we heard it again in 1995: “The young trees (4-8 years old) had a good crop, but the older trees just don’t have the set.”

There are several explanations for this phenomenon: Young trees have a high leaf:nut ratio, and bigger leaves (important in providing food for developing nuts). Young trees intercept more sunlight; each leaf on a young tree is more efficient as a food producing entity because it is less likely to be shaded by adjacent trees. And in young orchards there is better air circulation; blossoms on young trees dry faster, providing two benefits: more effective bee time and less chance for disease to take hold (fast-drying blossoms can be worth a fungicide spray).

With the entire focus on bloom-time weather, growers often overlook a crop input that can be equally important: post-bloom sunlight. Not only was bloom weather marginal last spring, but post-bloom storm systems and lower temperatures were not conducive to the retention of pollinated nutlets. This led to many orchards having excessive nutlet drop during March and April. This was a drop of pollinated nutlets that did not receive sufficient nourishments from light-intercepting leaves to be retained.

A well pollinated orchard sets a large number of nuts and these rapidly growing nutlets put a tremendous demand on the trees for food reserves. If this demand can’t be met, then nutlets drop. Young trees are better equipped to meet this demand.

Although no post-bloom sunlight studies have been conducted on almonds, an Oregon study on hazelnuts provides some interesting insights: trees were artificially shaded during the immediate post-bloom period and the effect on both nut set and nut size was dramatic. The researchers concluded that “shading during this period clearly reduces yield” and has an “astronomical” effect on the size of nuts. They explained that “the kernel is going through rapid cell division, and we think that shade during this period of development somehow impacts cell division within the kernel.” (1)

A 1989 study on apples showed a similar effect: the crop on (post-bloom) shaded trees was half that of control trees.(2)

The Fritz variety had the best crop of any variety in 1995, partly because most Fritz trees are relatively young, but also because the post-bloom nut development of Fritz is the slowest of any variety, thus putting less demand on a tree’s food reserves and less demand for post-bloom sunlight.

In years of below normal post-bloom sunlight, such as 1995, young trees and older orchards that have been opened up, are better equipped to take advantage of available sunlight.

Retention of Leaves

Recent UC studies have shown that the post-harvest irrigation is one of the most important inputs to attaining maximum almond yields. Post-harvest water allows trees to retain leaves during September and October, two normally sunny months. A study on pecans adds credence to the UC studies: “Removal of leaves prior to Oct. 1 resulted in no nuts set and no yield the next year.” (3)

Leaves can manufacture a lot of food during September and October and this food is stored in the tree to be parcelled out to the developing nutlets in the spring. Without sufficient food, nutlet drop will be excessive. It’s either bank some sunlight in the fall, or pray for sunlight in the spring. Growers with good crops in 1995 stored much sunlight in the fall of 1994.

A number of lessons can be learned from 1995:

  1. It’s worth taking measures to insure the strongest hives possible.
  2. That post-harvest irrigation is important – believe it!
  3. When planning an orchard, the diamond pattern – each tree equidistant from the other – is the best (note: a knock on the diamond pattern is that there is a dead space at the end of every other row; many growers compensate for this by crowding another tree into this dead space).
    Hedge-row plantings will give great yields during the first years of production, but will cause shading headaches when the trees reach full size. For crops such as apples, hedge-row shading provides a natural thinning mechanism that reduces thinning costs.
  4. Open up older trees to provide more post-bloom sunlight; shaded limbs on older plantings in 1995 were often devoid of nuts.
  5. Consider planting the Fritz variety. Fritz blooms with Nonpareil but harvests after Mission, so give careful thought to whether you can live with such a late harvest.
    As with any ag commodity, there’s much more opportunity to make money in a short-crop year than in a year when everyone has a good crop. Some almond growers will make twice as much money from the 1995 crop than from the 1994 crop. It pays to be prepared for a poor spring every year.

Joe Traynor is owner of Scientific Ag Co., Bakersfield, Calif.

References

  1. Made in the Shade, Sun-Diamond Grower, Fall 1995 pp 12-13.
  2. Seasonal Light Requirements in a Fruit Orchard, U. of Mass. Fruit Notes, Summer 1991, pp 20-21.
  3. Keep those Leaves on the Trees Until Frost, Pecan South, July 1995 p. 4.