Apple - CROP POLLINATION BY BEES

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.

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Macoun – do not cross-pollinate each other well. Likewise, spur types do not pollinate the parent variety well. The bloom periods of the main and pollenizer varieties must overlap. To optimize pollination, it is necessary to plant both early- and late-blooming pollenizers so that the main variety blooms in between. In that way, ample pollen will be available for the early-blooming king bloom on the main variety, and if frost kills the king blooms the late-blooming pollenizers will provide pollen for those flowers that remain.

Some apple varieties have sterile pollen. These varieties willingly receive pollen from other varieties and produce fruit, but they cannot Fig. 17.1. Flower of apple, Malus domestica. The flower has been partially dissected to reveal interior structures. (Source: (art) Darrell Rainey; (photo) Jim Strawser.)

Apple 145¹

Table 17.1. Apple varieties, pollen viability, and relative bloom periods for the southeastern US (from Horton et al., 1990).

Good pollenizer Pollen

Variety interplants viability Relative bloom period (days)

Winter Banana (Spur) ✓ Good X X X X X X X

Jersey Mac ✓ Good X X X X X X

Empire Good X X X X

Paulared Good X X X X

Stayman Not good X X X X

Yates ✓ Good X X X X X

Jonagold Not good X X X X

Delicious Good X X X X

Braeburn Good X X X X

Mutsu Not good X X X X

Jonathan Good X X X X

Granny Smith Good X X X X X

Arkansas Black Good X X X X

Gala Good X X X X

Golden Delicious Good X X X X

Fuji Good X X X X X

Rome Beauty Good X X X X X

Table 17.2.Apple and crabapple varieties and relative bloom periods for interior British Columbia (British Columbia Ministry of Agriculture, Fisheries and Food, 1994).

Variety Relative bloom period (days)

Dolgo X X X X X X X

Sunrise X X X X X X X X X X

Makamik X X X X X X X

Empire X X X X X X X X

McIntosh X X X X X X X

Golden Delicious X X X X X X X

Jonagold X X X X X X X X

Elstar X X X X X X X X X

Manchurian X X X X X X X X

Spartan X X X X X X X X

Red Delicious X X X X X X X X

Royal Gala X X X X X X X X

Rome Beauty X X X X X X X X

Fuji X X X X X X X X

Winter Banana X X X X X X X X

Granny Smith X X X X X X X X

Braeburn X X X X X X X

be used as pollenizers. Tables 17.1–17.4 list some apple varieties, their pollen viabilities, and relative bloom intervals for various regions of North America. Nursery stock catalogues also list main varieties and compatible pollenizers.

Insects are the only practical pollinators of apple. A mechanical power pollen duster device was shown to have no effect on fruit set, fruit size, seed number, or yield (Schupp et al., 1997).

Growers can use flowering crabapples as pollenizers instead of another commercial variety. This is warranted if other candidate pollenizers produce inferior fruit, take up too much orchard space, have conflicting pesticide requirements, or produce fruit that pickers cannot distinguish from the main variety. The flower colour of a crab variety should match the colour of the main variety since bees do not readily switch to a different-coloured blossom during a foraging trip (Mayer et al., 1989b). Crabapples can be planted in existing space between main variety trees or grafted on to them; this makes crabapples an attractive remedy for old orchards that were not inter- planted with pollenizers.

One can cut bouquets of flowering crabapples (or of any pollenizer) and place them in barrels of water between rows during bloom.

Such bouquets should be cut only when the king bloom is open, and they should be made large. It is helpful to change water when blooms begin to wilt and to place bouquets in sunny, still areas.

Because crabapples bloom on 1-year-old wood, crabapples should be pruned immediately after bloom in order to get them ready for next year. Some crabapples are more susceptible to virus diseases, but whole-tree crabapple plantings, rather than grafts, can reduce this problem. If crabs are grafted into virus-infected main variety trees, the grafts may fail because of virus-induced graft incompatibility.

Bees prefer to work up and down rows rather than across rows.

This is especially true in dense plantings and during even the lightest wind. One must consider this when planning the arrangement of main

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Table 17.3. Apple varieties and suitable pollenizers for interior British Columbia (British Columbia Ministry of Agriculture, Fisheries, and Food, 1994).

Main variety Pollenizer

McIntosh Crabapples Dolgo and Garry, Discovery, or other early-blooming variety

Spartan Red Delicious, Golden Delicious, Winter Banana Golden Delicious Spartan or Red Delicious

Red Delicious Spartan, Golden Delicious, Spur Winter Banana

Empire McIntosh

Jonagold McIntosh, Empire, Spartan

Gala, Braeburn, Fuji These can pollinate each other. Red Delicious, Granny Smith, and Winter Banana are also suitable pollenizers

Lodi Earligold Jonamac Gravenstein McIntosh Spartan Liberty Idared Scarlett Gala Akane (Prime Red) Jonathan Stayman Jonagold Mutsu (Crispin) Cotland Empire Enterprise Golden Delicious Red Delicious Spur Winter Banana Winesap Newton Pippin Granny Smith Fuji Braeburn Ramey York Rome Northern Spy Lady

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0 0 0 0 0 0 0 0 X

0 0 0 0 0 0 0 0 XXXXX

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 XXXX

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

XXXX 0 0 0 0

X 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0

X 0 0 0 0

Table 17.4.Apple varieties, compatibilities, and season of bloom for the north- western US. Blank boxes indicate suitable pollenizer combinations. A ‘0’ indicates varieties that are not suitable pollenizers for each other. An ‘X’ indicates that the variety is partially self-fruitful but should not be planted in solid blocks.

Variety pollinated

Early bloom

Midseason bloom

Late bloom

Pollen source variety

and pollenizer varieties in an orchard. With orchard plan 1, every other tree is a pollenizer (Fig. 17.2); this maximizes the number of pollenizers, but it is practical only if there is a market for the pollenizer.

All other plans compromise some degree of pollination efficiency in favour of convenience at harvest. With plan 2, every third tree in every third row is a pollenizer (Fig. 17.3); this ensures that every tree of the main variety is next to, diagonal to, or across from a pollenizer on one side. Plan 3 calls for a solid planting of the pollenizer every fourth row (Fig. 17.4); this leaves one row of main variety by itself and is practical only if the pollenizer has market value. Plan 4 calls for two pollenizer rows next to four rows of the main variety (Fig. 17.5);

this is the least efficient design. Main varieties and their pollenizers should not be planted in the same row, as in plans 1 and 2, if they cannot withstand the same chemical regimen. Instead, pollenizers should be planted in their own rows so that they can be treated sepa- rately, as in plans 3 and 4. Crabapple pollenizers can be pruned for tall growth to take up little or no extra space. In this manner, they can be planted as every sixth to ninth tree in every row.

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Fig. 17.2. Plan 1 orchard design for encouraging apple cross-pollination. Every other tree is a pollenizer. (Source: Carol Ness.)

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