Honey bees as almond pollinators
Honey bees are the most important pollinator of almond in the US (Table 16.3). They readily visit almond flowers and effectively polli- nate them. Because almond’s pollination demands are so high, it is doubly important to use strong colonies. The goal is to have colonies at peak strength at the time of peak bloom. An acceptable colony will have eight frames of bees – a ‘frame’ meaning one standard deep frame two-thirds to three-quarters covered with bees at 60°F (15.6°C) (Traynor, 1993) – and 800 in2 (5200 cm2) of brood (McGregor, 1976).
However, because the bloom season for almond is so early in the year it is sometimes difficult for bee-keepers to have colonies at full strength. Bee-keepers can stimulate colony growth with a mid-winter feeding programme, but this is costly and many choose instead to rent weaker colonies at a reduced fee. Most almond pollination contracts are based on an average number of frames of bees; a grower that wants a minimum frame standard must be willing to pay a higher fee because every colony must be inspected. County agriculture commis-
140 Chapter 16
Table 16.2. Bloom period of almond varieties relative to ‘Nonpareil’. Numbers indicate days before (2) or after (+) average peak ‘Nonpareil’ bloom (Traynor, 1993).
Early Early-mid Mid Late-mid Late Very late
Ne Plus (26) Sonora (23.5) Nonpareil (0) LeGrand (+3) Butte (+5) Ripon (+12) Peerless (22.5) Jeffries (0) Tokyo (+3) Padre (+5) Planada (+14) Milow (21) Price (0) Drake (+3) Thompson Tardy Nonpareil
(+5) (+17)
Kapareil (+1) Monarch (+3) Livingston (+5) Suaret #1 (+1) Suaret #2 (+3) Mission (+5) Carmel (+2) Norman (+4) Mono (+7)
Monterey (+2) Yosemite (+7)
Carrion (+2) Ruby (+8)
Fritz (+2.5) Merced (+2.5) Harvey (+2.5) Solano (+2.5)
sioner offices, private consultants, and some brokers offer colony strength inspection services.
A second problem posed by early-blooming almond is cool wea- ther. Honey bees do not fly readily until temperatures exceed 55°F (12.8°C). One way to minimize this problem is to put hives in sunny, wind-protected locations to encourage good flight. If cool tempera- tures persist, it may be necessary to increase hive density in order to compensate for reduced flight efficiency.
With many other crops it is advisable to bring in bees after some bloom has already begun. This is not the case with almond because the earliest blooms are the most productive. Moreover, there is usually little else blooming to distract the bees, and honey bees eagerly visit almond as soon as it starts blooming. So, there is no reason to delay the arrival of bees and most growers bring in bees as soon as the crop blooms, or earlier. If early-blooming apricots, mustard, or peaches are present to compete with almond, a bee attractant may help (see Chapter 7, page 58). However, there is no evidence that bee attractants are effective on almond (M.L. Winston, Simon Fraser Univ., personal communication).
McGregor (1976) recommends placing colonies within an orchard in groups spaced !a;mile (160 m) apart. But it seems that having strong colonies is more important than their distribution in the orchard.
Growers achieve good results when large groups of strong colonies are placed along roadways !f–!smile (0.4–0.8 km) apart within the orchard (Traynor, 1993). As with other crops, bee hives placed together in large groups perform better than hives distributed singly. Hives in California are usually deposited in groups of 16, 24, or 32.
Webster et al. (1985) showed in almond orchards that honey bee hives fitted with pollen traps fielded a higher proportion of foragers collecting pollen compared to non-modified hives. This potential benefit, however, was partially offset by a slower rate of growth in those colonies with traps.
Almond 1411
Table 16.3.Recommended bee densities for almond.
No. of honey bee hives acre21(ha21) Reference
2–3 (5–7) McGregor (1976)
1–3 (2.5–7) Thorp and Mussen (1979)
3–4 (7–10) Levin (1986)
2 (5) Traynor (1993); Scott-Dupree
et al. (1995)
2.5 (6) Literature average
Other bees
3 O. cornuta females per tree (in Spain) Bosch (1994b)
Orchard mason bees as almond pollinators
Two orchard mason bees are potential pollinators of almond – the North American native blue orchard bee (O. lignaria propinqua) and the orange orchard bee (O. cornuta) from Spain (Chapter 12). When introduced into California almond orchards, both bees collect almond pollen, occupy man-made nests, and develop normally on a diet of almond pollen and nectar (Torchio, 1981a,b; Torchio et al., 1987).
However, many females disperse away from February release sites before nesting. These bees are good pollinators; in Spain, each O. cor- nuta female visits 9500–23,600 almond flowers during a season, and only three females per tree are needed to maximize pollination (Bosch, 1994b). However, the technology for their large-scale, practical use is not yet developed.
142 Chapter 16
Flowering
The apple (Malus domestica) flower occurs in a cluster of flowers at the end of a 1–3-year-old woody shoot called a spur. The flower has five stigmas that join into a style that leads to the ovary (Fig. 17.1).
The ovary has five divisions, each with two ovules, which means that a fully-pollinated fruit will have ten seeds (the variety ‘Northern Spy’
has four ovules per division for a maximum of 20 seeds).
Surrounding the style are 20–25 pollen-bearing stamens. Nectar is excreted at the base of the central style. Five pinkish-white petals surround the sexual parts. Each flower cluster has a primary bud called the king bloom that opens first and produces the best fruit.
Production of nectar and pollen is marginal to good, and bees readily visit the blossoms.