Introduction

The apple cultivar Empire is an open-pollinated seedling of McIntosh selected at Geneva, New York and named in 1966. Since its release this cultivar has gained moderate market acceptance and is now being widely planted. Empire is a McIntosh type that overcomes some of the problems associated with McIntosh. This cultivar, while not as easy to grow as McIntosh, is very precocious and can be a consistent annual producer. The fruit is firmer, develops more red colour than McIntosh and stores well. The tree does not exhibit strong vegetative growth at maturity and fruiting effectively slows total tree growth as well. The fruit colour of Empire is naturally good in properly pruned canopies, preharvest drop is not a problem, and properly matured and harvested fruit stores well.

Empire requires attention to detail in the orchard management program if long-term production of superior crops is expected. Empire is very fruitful and has a heavy spur system, although the tree is not a true spur type. Shoot and secondary branch growth should be maintained, especially in the fruiting tree. Loss of active shoot growth is rapidly followed by the development of a "spurbound" condition and loss of fruit size.

Encouragement of vigourous vegetative growth in the first years in the orchard is mandatory for successful training and canopy development of Empire trees. Proper pre-plant soil preparation, correction of drainage, pH, replant or other soil-related problems, selection of well-grown, vigourous nursery stock, and planting as early in the spring as possible all help to produce strong tree growth.

Central leader training

The most desirable tree shape for maximum fruit quality and ease of management is conic, with the bottom limb spread wider than above and as wide or wider than the tree is high. The conic tree shape favors uniform light distribution and optimum light interception. The best way to encourage a conical tree shape is to maintain a strong central leader.

Training this cultivar to a central-leader when the tree is free-standing is often difficult. Without physical support and proper management, the central leader tends to be weak and fails to continue vertical growth. The weaker rootstocks, such as M.9, M.26 or interstem root systems, aggravate this tendency. If the leader is not kept strong, dominant, and in the centre of the tree, some lower scaffold limbs are ultimately shaded out. In addition, loss of the leader makes it impossible to properly develop the conical shape of the tree.

Empire lends itself well to tree support and growers have been well satisfied with versions of the slender spindle and vertical axis training systems. If the leader is supported for the life of the tree, production can be encouraged earlier and the conical tree shape is achieved. The minimal pruning involved in supported systems translates into longer extension growth and a more productive tree in the juvenile years.

To encourage leader dominance in free standing central leader trees, cut 1/3 to ½ off the leader's new growth during the dormant season each year. This cut usually stimulates the development of more than one vigourous shoot. A single leader shoot should be selected by removing the 1 or 2 upright competitors shortly after bloom or when the new shoots reach 5-10 cm in length. When this procedure is carried out for the first several years in the orchard, a satisfactory leader should develop in trees of good vigour (Figure 1). If the leader shows a tendency to tip out of the tree or if vigour is low, the tree should be staked. Staking forces the leader to assume a vertical position and permits continued development of upper tiers of scaffolds. On windy sites, staking young Empire trees is essential for proper canopy development.

Six-year-old Empire/M.26 EMLA tree showing the good central-leader and scaffold-limb development available in trees of good vigour when corrent training and pruning methods are used.
Figure 1. Six-year-old Empire/M.26 EMLA tree showing the good central-leader and scaffold-limb development available in trees of good vigour when corrent training and pruning methods are used. Note scaffold positioning vertically on the leader and around the leader to produce an open, productive canopy.

Should the leader be lost, it will be difficult to regain. If this happens, a vigourous upright shoot in the centre of the tree is selected. This shoot should be trained to become the leader by removing competition from nearby shoots or fruit, and heading during dormant pruning. This method of leader renewal may be required up to three times during canopy development in unstaked trees.

Maintaining leader strength

The natural strength of the leader is dependent on several factors. A large number of scaffold limbs originating too close together on the trunk will weaken the vigour of the leader. The trunk should taper smoothly from bottom to top. Abrupt changes in trunk diameter over a short distance indicate that growth and nutrients are being diverted into lateral limbs, resulting in a weak leader. To reduce this tendency, the first tier of scaffolds should not have more than 4 branches. These limbs should be distributed so that each points to a different quadrant in the tree, with each limb base vertically separated from its nearest neighbor by at least 10 cm. Normally the first tier of limbs should be distributed on the trunk from knee height to waist height.

When a lateral branch develops whose basal diameter is similar to that of the leader, this branch is best removed. Spreading will be too difficult, as this limb is very vigourous.

Fruiting on the leader should be discouraged during the canopy-development phase. Fruiting competes strongly with shoot growth, weakening it, and the weight of fruit can physically bend the leader (Figure 2). The earlier in the season that fruit are removed from the leader, the better. 

A 5-year-old Empire/M9/MM106 interstem tree that lost its central leader because fruit were not removed the previous year.
Figure 2. A 5-year-old Empire/M9/MM106 interstem tree that lost its central leader because fruit were not removed the previous year. Note the top of a 1 m stick indicating the height at which the leader was lost. Further upward canopy development has been stopped completely and no suitable vertical replacement shoots have arisen yet.

Training and early production

By the second or third year, Empire trees should be ready to carry a small crop. As soon as production starts, vegetative growth will be reduced. Therefore, the crop load should be carefully controlled in young Empire trees to assure proper canopy development. Both early cropping and the subsequent control of vegetative growth are of paramount importance in a high-density planting. Empire usually tends to crop too early. The trees should not be cropped until the leader and the first tier of scaffolds are well established and can carry a crop without bending out of position (Figure 3).

Proper regulation of cropping in a 4-year-old Empire/M26 tree.
Figure 3. Proper regulation of cropping in a 4-year-old Empire/M26 tree. Note the continuation of central-leader development and scaffold-limb selection in the upper canopy, from which all fruit were removed shortly after bloom. Lower scaffolds are allowed to crop only to the extent that they can carry the fruit without bending out of position and can continue good vegetative growth.

By this time the second tier of scaffolds will be developing. If the young tree is over-cropped, the leader could be lost, and the scaffolds will turn down with the weight of the fruit, restricting further development. Such a crop will cancel all previous efforts to establish an adequate tree structure. The physiological damage to the tree will be even greater, as the tree will be stunted. The first tier of limbs will not fill the allotted space and total production will not be up to expectations.

As the tree gets older the conical shape must be maintained. If the higher tiers of branches outgrow the lower tiers, shading will produce a fruit-colour problem. This situation will also lead to excessive pruning to correct the poor canopy shape. Fruit forming on the terminal portions of the limbs has greater leverage, increasing the possibility of limb bending.

Heading of lateral limbs is usually not necessary and should only be done if retardation of fruiting and increased extension growth is required. Such is the case if the trees are small and not growing well. Growth is more crucial than fruiting at this point and heading lateral growth may improve vegetative vigour. This approach will not produce satisfactory results if poor tree growth originates from unfavourable soil or soil-moisture conditions, winter injury, or pest damage.

The spreading of limbs is usually not necessary. Wide, sturdy crotches usually develop with no special assistance. Occasionally, a desired limb may require spreading. The limb-to-leader angle should be maintained at about 45 - 60° for free standing trees and about 60° for supported systems. Limbs spread to near the horizontal tend to stop growing and become weak. Limbs not spread far enough will remain vigourous and will grow into the space to be occupied by other scaffolds, creating undesirable shading.

At maturity

Empire trees should be maintained with well-opened canopies to allow uniform light distribution to all parts of the tree. Total scaffold numbers should be adjusted depending on tree size and support system so that maximum light exposure to all leaves and fruit is maintained. Only about 10% of the light that strikes a leaf passes through, thus limiting the light available to shaded leaves and fruit. A thick tree is not capable of producing the quality and size of fruit that a well-opened tree can.

As the tree becomes older a system of scaffold maintenance and renewal becomes necessary. Older, spurbound scaffolds will decrease in productivity, fruit size and fruit colour and should be replaced. Two or more scaffold limbs should not be positioned in the same quadrant of the tree unless the vertical distance between them is at least 60–80 cm. If scaffolds grow one directly over the other, shading becomes a problem, spur vigour declines, fruit colour and size decrease. As scaffold limbs fill their allotted spaces, thinning-out cuts are necessary to maintain vigour and to contain the limb. When thinning out a limb, cut back to a lateral that will redirect the growth to an unshaded location in the tree. A combination of thinning out of spurs and heading back of weak wood is used to stimulate vegetative growth.

Heading-back cuts should be made in older wood to force more shoots to develop. Heading new growth to stimulate more growth may also be necessary. If a limb has become too large for its position and a weaker limb above or below can use the same space, the larger limb should be removed. This approach is critical in higher density supported systems. Care must be taken to maintain a moderate amount of shoot growth along with healthy spurs to obtain acceptable fruit size. This scaffold renewal system works well on Empire and should be part of the annual pruning procedure in a mature tree.

Fruit size

Genetically the fruit of Empire tends to be of medium size. The abundant spur system predisposes the tree to set heavily. A heavy set makes adequate fruit size difficult to obtain. The limited vegetative growth common in mature trees can also be a major factor in limiting fruit size.

A healthy and abundant supply of spur leaves is crucial for the set and early development of the fruit of apple trees. Later on in the season the shoot leaves become important contributors to the further sizing of fruit. As Empire trees get older, fruit size may decrease if the trees are allowed to become spurbound with little shoot growth. The spurs also become weak with age and with shade, reducing fruit set and size. In this weakened state the tree will usually not respond adequately to nitrogen, fruit thinning, or irrigation.

In Empire, the king blossom produces a larger fruit than lateral flowers in the clusters. Setting a large number of king blossoms produces a moderate fruit-size advantage. Locations where frost problems are common during bloom should be avoided. Empire is sensitive to frost damage and king blossoms are often damaged more seriously because they develop a few days earlier than lateral bloom. Similarly, if the spur leaves are injured by frost, then fruit set and early development will be adversely affected. Empire appears to be acclimated to the same growing conditions as Delicious. In areas where Delicious grows well, Empire is expected to do well with proper management. The largest fruit will be grown in the warmer production areas.

Cross-pollination is required for consistent crops of Empire; pollenizers should be chosen with the goal of setting the king bloom. That king bloom should also be set with a full compliment of seeds. The pollenizer should be in flower just before the king flowers on Empire. Cultivars such as Idared, McIntosh, Gala and Cortland appear to be adequate pollenizers for Empire. A good rule of thumb in orchard design is to have the pollenizers within 35 m of the Empire trees. Pollenizer trees should make up at least 15–20% of the trees in the orchard to assure good pollination and fruit set.

Adequate levels of nitrogen (N) are necessary to encourage good shoot growth and fruit size. Leaf nitrogen levels of 2.1–2.5% are necessary for acceptable shoot growth and adequate fruit size. A young Empire tree will quickly drop from a high level of N to a lower and possibly inadequate level when in production. Over-fertilization with nitrogen should also be avoided, as fruit colour will become a problem. Empire is sensitive to marginal or low levels of potassium, and heavy cropping accentuates this problem. Calcium (Ca), magnesium (Mg), zinc (Zn), and copper (Cu) give no positive response unless a clear deficiency exists. Leaf analysis is recommended at regular intervals to be sure that the levels of all nutrients are sufficient to support a full crop of quality fruit.

Soil moisture can be a problem for fruit size if there is a period of prolonged deficiency. Because of the natural tendency of Empire to set heavy crops and produce moderate fruit size, a soil moisture deficiency simply aggravates a fruit size problem. The texture of the soil, its moisture-holding capacity, the amount of rainfall and its distribution, and the crop load all affect fruit size. Cropping limits the growth of roots more than any other part of the tree. A heavily cropping tree does not develop as extensive a root system as a light cropping tree. Heavily yielding trees will require a greater available water supply than trees producing lower volumes of fruit. In high-density plantings with weak rootstocks, root activity can be significantly reduced by heavy cropping, increasing the possibility of obtaining a favourable response to supplemental irrigation.

Fruit size in Empire is not influenced substantially by most rootstocks, however the following differences have been noted. The rootstocks M9, M26, M7, MM106, interstems (MM111 or MM106 plus M9) and MM111 have been used successfully. M26 can give better fruit size, but the tree can be a challenge to grow, especially on poor soils or windy sites. M9 will likely produce the largest apple for any given crop load, while MM111 may give the poorest size.

Thinning

Empire is as hard or harder to thin than McIntosh, and the older the tree, the more difficult it is to thin. As with other cultivars, frost during bloom does sensitize the tree, increasing the likelihood of easier thinning. The more that the crop is thinned, the larger the size of the fruit. It is important to remember that successful thinning is accompanied by a loss in yield, and that fruit size does not increase to the same degree that yield is decreased. The thinning program should be adjusted to the minimum level consistent with acceptable fruit size and good return bloom.

The ideal distance between apples on a branch is 10–15 cm (one hand width). Anything greater indicates significant yield loss. Carbaryl (Sevin) alone as a thinner is usually not adequate. Good results have been obtained where naphthaleneacetic acid (NAA) was applied at 7–10 ppm (part per million), 10–14 days after full bloom. Higher rates may be needed on older trees. Thinners are usually applied from 7–21 days after full bloom, depending in part on fruit growth. If fruit growth after bloom is rapid, thinners should be applied earlier within that time range.

A combination of 2.5–4 ppm NAA plus carbaryl (0.5 kg active Sevin/500 litres water) may be required on older trees that are hard to thin. Accel® can be used as a thinner and it has the potential to improve fruit size independent of thinning. Trials where Accel® and carbaryl (Sevin) were used in combination have given good results. Accel® used at 50 ppm of B.A. (active ingredient) plus 1 litre of Sevin XRL Plus per 1000 litres of water, thoroughly wetting the tree, have shown promise. Fruit was effectively thinned and the size of the resulting fruit was increases over the response of thinning alone. Accel® must never be used in the same season as NAA or fruit problems may result. All thinners require several days to show their effect, and low temperatures after thinning delay the visible response.

Even lightly set crops should be thinned to break up clusters and thus improve colour. Light crops resulting from frost are no exception and should be thinned, with a reduced rate of thinner, to break up clusters. If mostly lateral blossoms have set, thinning results will likely be more variable, due to the equal strength of the lateral fruits forming in the cluster.

For good fruit size, the key factors are to maintain good vegetative vigour with adequate nitrogen and pruning, to set canopy king blossoms with adequate pollenizers, and to properly thin the resulting crop. Attention to these details is definitely required for long-term production of quality fruit.

Harvest date

Rootstock does not appear to affect the harvest date significantly. A common error made at harvest is to leave 'Empire' on the tree to get superior colour. Empire should be picked just ahead of Delicious. When left on the tree too long the storage quality drops quickly. For more details on when to harvest Empire, consult OMAFRA fact sheet Evaluating maturity of Empire, Idared and Spartan apples.