Improved Pollination Will Improve Yields: Some History to Back This Up

Pacific Nut Producer, February, 2004

By Joe Traynor, Contributing Writer

California’s 2002 almond crop broke the billion-pound barrier and almond orchards averaged an astounding 2,060 pounds (nut meats) per acre. It wasn’t very long ago that one ton of nuts was the goal of every almond grower. In 2002, there were a number of 3,000-pound-per-acre yields and a handful of 4000-pound-per-acre crops. Everyone expected the 2003 crop to drop off considerably, however the estimates indicate a 1,700-pound-per-acre crop.

Considering that average yields in the 1960s were well under 1000-pounds-per-acre, the recent high yields are nothing short of phenomenal.

With improved technology, yields of all agricultural crops have increased over the past 30 years, but no crop can match the yield spike in almonds over this period. For example, a comparable tree crop, prunes, showed a commendable 22 percent yield per acre increase for the five-year period 1998-2002, compared to 1965-1969. Compare this to almonds, which showed an amazing 116 percent increase during the same period.

Improved management practices could well account for a 22 percent increase in yield (in both prunes and almonds) and it is possible that better than average weather during the bloom period have added to the increase in recent years. Many in the almond industry point to what is the most likely explanation for current record yields: improved pollination. This improved pollination is due to two factors: selection of varieties that overlap in bloom and orchard layout of these varieties.

The first almond plantings in California followed the recommended pollination layout for apples: planting of early, mid-blooming and late-blooming varieties in one block, with the main variety comprising at least two-thirds of the orchard. As late as the 1950s, early-blooming NePlus, mid-blooming Nonpareil and late-blooming Mission were popular plantings. Such a variety mix would be fine for apples, which require only a 10 percent set of flowers for a satisfactory crop, but the arrangement doesn’t work for almonds where 50 percent set of flowers is needed for maximum yields – depending on the number of flowers. Considering that an almond flower is only receptive to pollination for a few days, relatively low yields on early plantings were the norm.

Many of the early almond plantings had three rows of Nonpareil alternating with one row of a pollinizer variety. Such plantings were popular for two reasons: nut handlers prefer the Nonpareil over other varieties and harvesting is much easier when two or more adjacent rows are the same variety.

When the inside Nonpareil row in 3:1 plantings came up noticeably short in crop, 2:1 plantings became the standard, with the Merced and Carmel varieties serving as pollinizers for Nonpareil. To the surprise of many, tests showed that on 2:1 plantings, nut set on the inside of the two Nonpareil rows was as much as 30 percent lower than on the side of the tree adjacent to the pollinizer row.

Today, virtually all almond orchards that yield 3000-plus pounds-per-acre are planted to a 1:1 or 1:1:1 pattern, with the Nonpareil variety comprising 50 percent of the acreage on such plantings. The Merced variety has given way to Fritz, Carmel (free of bud-failure), Monterey and some others as pollinizing varieties. Late-blooming varieties (Mission, Padre, Butte and Ruby) are planted together in separate blocks (Butte is the earliest blooming of this group and is occasionally planted with Nonpareil and in some years blooms with Nonpareil).

Fifty years ago, the Nonpareil variety comprised around 60 percent of California’s almond acreage compared to less than 40 percent today. The price difference between Nonpareil and late-blooming hard-shells has increased from 10 cents per pound to as much as 40 cents per pound.

Almond producer Alan Scroggs (of Scroggs Consulting) has carried pollination layout about as far as it can go on a 80-acre block near Shafter. Alan is alternating Fritz with Nonpareil (every other tree) in the same row and Carmel with Nonpareil (every other tree) in the adjacent row (giving 50 percent Non-pareil, 25 percent Fritz and 25 percent Carmel. In addition, Alan has planted every 10th row to the promising new Blue Gum variety. It will take extra work to harvest the varieties separately, but Alan feels it is worth it. “Pollination is the key to getting top almond yield,” said Alan, “and our planting arrangement should maximize pollination.”

What about bees? It only takes one pollen grain from a compatible variety to set an almond and the high populations of honeybees seen in orchards at bloom time should be able to easily accomplish this transfer. For varieties that are 50 percent compatible (See Table 1) it takes a minimum of two pollen grains per stigma to set a nut. With 50 percent compatible plantings, bees have to transfer twice as much compatible pollen to effect nut set.

Table 1

Incompatible and 50 percent compatible Almond Varieties

Almond varieties get a gene from each parent. If the two genes are identical to the two genes in another variety, the varieties are incompatible and will not cross-pollinate. If one of the two genes in one variety is the same as one of the two genes in another variety, the varieties are 50 percent incompatible, meaning half the pollen from one variety will not pollinate the other. Incompatible and 50 percent compatible varieties usually have similar parentage. The large number of varieties that are only 50 percent compatible with with Nonpareil are due to Nonpareil being used as a cross in the development of other varieties. Some incompatible and 50 percent compatible combinations are given below. Contact your nursery or your farm advisor for compatibility data on other combinations.
Incompatible (will not set nuts with each other) 50 percent Compatible (Only half the pollen will set nuts)
Butte/ Monterey
Butte/ Avalon

Price/ Aldrich
Price/ NePlus

Aldrich/ NePlus
Monterey/ Avalon
Sauret#1/ Carmel

Nonpareil with: Aldrich, Avalon, Butte, Carmel, Merced, Monterey, NePlus, Price, Sonora, Tokay and Wood Colony.

Butte with: Aldrich, Fritz, Mission, Nonpareil, Padre, Price, Ruby, Sonora and Winters.

Mission with: Butte, Padre and Ruby.

Winters with: Aldrich, Avalon, Butte, Fritz, Monterey and NePlus.

Many more pollen grains that are incompatible are deposited on a flower’s stigma than compatible pollen grains. This incompatible pollen is not “wasted” because it stimulates the growth of compatible pollen. One hundred or more pollen grains are needed to provide this stimulus, called the “mentoring effect” by noted pollen expert Tom Ferrari. Since an almond flower produces 50,000 pollen grains per stigma, most of the incompatible pollen on the stigma is “self” pollen and this “mentoring pollen” should be easily provided by one or two honey bee visits (individual almond flowers probably receive more than 50 honey bee visits during bloom).

There are many commercial plantings of 50 percent compatible varieties (mainly Nonpareil/Carmel plantings) and yields on these orchards have reached 3,000 or more pounds per acre, indicting that pollination has been more than adequate even though twice as much pollen needs to be transported by bees to effect nut set. One hundred percent compatible plantings (e.g., Nonpareil/Fritz) should require half as many bees as 50 percent compatible plantings, since the required amount of work is half as much. Wouldn’t you use only half as many workers to carry 50 ladders from one end of your orchard to the other in the same amount of time as you would 100 ladders? If two bee colonies per acre are giving 3,000 pound yields on 50 percent compatible plantings (Nonpareil/Carmel) then one colony per acre would be more than adequate on 100 percent compatible plantings (Nonpareil/Fritz).

An almond orchard produces about five pounds of almond pollen per acre and tests with pollen traps show that honeybees collect close to five pounds of almond pollen each season. Considering that Blue Orchard Bees collect only about five ounces of pollen at recommend populations, almond growers, especially growers with 100 percent compatible varieties, are probably placing too many bee colonies on their orchards.

The current robust health of the almond industry (due mainly to lack of global competition) has created considerable interest in new almond plantings. Today’s 530,000 bearing acres is putting a strain on the supply of honeybee colonies at the two-colony-per-acre rate.

There has been a shortage of strong bee colonies for almonds in recent years and with U.S. bee colony numbers staying stagnant, the supply of bees for almonds can only get tighter as almond acreage pushes over the 600,000-acre mark. Planting only 100 percent compatible varieties and cutting back from two colonies per acre to one colony per acre would go a long way towards eliminating the impending bee shortage for almonds.

Joe Traynor is a bee-broker and owns Scientific Ag Co. in Bakersfield. Much of the information in this article comes from studies by Robin Thorp and Tom Gradziel, both of U. C. Davis. These studies were funded by the Almond Board of California.