Apple Rootstocks for High Density Orchards

Commercial fruit growers are transitioning their apple orchards to high density production systems, and this is possible due to the availability of size-controlling apple rootstocks.
Apple Rootstocks for High Density Orchards - Videos

Description

There are many dwarfing rootstocks currently available, and selecting the correct rootstock for your management style and site takes advanced planning.

Instructors

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Michael Basedow

View Transcript

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- [Instructor] Many fruit growers across the state are now growing a portion of their apple trees in high density production systems.

This is possible due to the availability of size controlling apple rootstocks.

There are many dwarfing rootstocks currently available, and these provide many benefits to the fruit grower.

However, there is no perfect one size fits all rootstock.

With the various clones of M.9 and promising new rootstocks being released from breeding programs, it can be difficult to choose what to plant your next block on.

In this video, we will review rootstocks that have been trialed in Pennsylvania research blocks and that are recommended for planting in commercial orchards.

Keep in mind that rootstock performance can be variable across different field sites, so it is important to trial a new rootstock on your site before establishing a large planting.

In addition to controlling tree size, dwarfing rootstocks provide many additional benefits, including increased precocity and productivity which allows the trees to come into production earlier and to produce more fruit relative to its tree size.

Many rootstocks have been bred to be cold hardy, an important feature in our cold northeast winters.

Many clonal rootstocks have been for disease resistance.

The Geneva series rootstocks, for example, are bred to be resistant to fire blight, Phytophthora crown and root rots, and replant disease.

Dwarfing rootstocks also tend to have better growth habits, including improved branch angles.

These improved habits allow for increased light interception, allowing for the production of higher quality fruit.

Malling 9 or M.9 is one of the most widely planted dwarfing rootstocks, and its various clones are still considered the industry standard for high density plantings.

It produces a truly dwarf tree about 35% the size of a standard seedling rootstock, and fruit tend to be well-sized.

This rootstock is also very precocious and will produce some fruit the year after planting.

It is resistant to root and crown rot but performs best in well-drained sites.

M.9 is susceptible to fire blight and wooly apple aphids and is prone to developing burr knots.

There are many clones of M.9 available.

The main differences are found in their tree size.

There are listed from the most to least dwarfing.

M.9 Fleuren 56 and T337 produce trees slightly smaller than the traditional M.9, about 30 to 35% the height of a standard tree.

M.9 337 is one of the most popular rootstocks currently used in Tall Spindle plantings.

M.9 EMLA is a virus-free clone from the East Malling and Long Ashton research stations.

It is approximately 25 to 30% more vigorous than the original M.9.

While still commonly found, it is becoming less popular compared to the other vigorous M.9 clones.

M.9 Nic 29 is a Belgian clone of M.9 that is 35% more vigorous than 337.

Pajam 1 and Pajam 2 are French selections that are relatively new.

They are 35 to 40% more vigorous than M.9 337.

In this image, you can compare the tree growth of Fuji on a weak and strong M.9 clone.

M.26 produces a larger tree than M.9, about 40% the size of a standard seedling apple, and can produce a dwarf or a semi-dwarf tree, depending on the scion, production system, and soil type.

It is precocious, productive, and winter hardy, and produces few root suckers.

M.26 is susceptible to fire blight and collar rot and should not be planted on wet sites.

It is also prone to developing burr knots, so precautions are needed to prevent the establishment of dogwood borers.

Some varieties, like Rome, Stayman, Golden Delicious, Honeycrisp, and many triploids produce weak unions on M.26 and should not be planted on this rootstock.

The Budagovsky series of rootstocks were developed in the former USSR.

A well-known release from this series is Budagovsky 9, or Bud 9 for short.

Bud 9 produces a tree that is slightly smaller than M.9, about 35% the size of a standard seedling.

In the image you can see the difference in growth between McIntosh on M.9 on the left and Bud 9 on the right.

Bud 9 is very cold hardy.

It is resistant to collar rot and has some resistance to fire blight, becoming more resistant as the tree ages.

It produces few suckers, but does produce burr knots.

Bud 9 has slightly higher yield efficiency than M.9 and performs well across a variety of conditions.

However, it may be too small of a rootstock for some low vigor cultivars.

Budagovsky 10 in a similar size category to trees on M.9 337 in Pennsylvania conditions.

You can see in the photos how Fuji performs on Bud 10 compared to Bud 9.

Bud 10 is cold hardy and resistant to fire blight.

It also produces trees with wide branch angles and has slightly higher yield efficiency than M.9 337.

It has good root anchorage and stress tolerance and is recommend for further use in Pennsylvania.

However, availability of this rootstock may be limited.

The Cornell/Geneva rootstocks were developed by Cornell and the USDA in New York.

The breeding program aims to develop dwarfing rootstocks that are cold hardy, resistant to fire blight, crown rot, wooly apple aphids, and tolerant of replant disease.

Geneva 11 is one of their releases and tends to produce a tree in the same size category as M.9 337.

G.11 is resistant to fire blight, but is not resistant to wooly apple aphid.

G.11 is partially tolerant of replant disease and moderately tolerant of crown and root rot.

It is cold hardy and has tolerance against latent viruses.

G.11 produces few burr knots and root suckers and also has a high yield efficiency.

G.16 is also in the M.9 337 size category.

It is resistant to both wooly apple aphid and fire blight, it is tolerant of crown rot, and has some tolerance to replant disease.

While G.16 has good midwinter hardiness, it is slow to acclimate and does not do as well during early cold temperatures in the fall.

It is also very susceptible to latent viruses, so it is imperative that only certified virus-free scions are budded to G.16.

G.41 is also similar in size to M.9 337.

It is very resistant to wooly apple aphids and fire blight and is tolerant of replant conditions and Phytophthora crown and root rots.

It is cold hardy and less susceptible to latent viruses.

It has higher yield efficiency than M.9 and produces few root suckers or burr knots.

G.41 may produce weak graft genes with some varieties during the first year or two in the orchard, so extra care should be taken if planting Cripps Pink, Scilate, or Honeycrisp on this stock.

This condition appears to be worse in the nursery and is less of an issue on older trees in the orchard.

G.935 is in the same size category as M.26.

Trials in Centre County found Golden Delicious were 12% smaller on G.935 compared to M.26.

It is resistant to fire blight but is susceptible to wooly apple aphid.

It is also tolerant of replant disease and Phytophthora root and crown rots.

Though it is close in size to M.26, yield efficiency is similar to M.9.

It also produces few root suckers.

935 is somewhat susceptible to latent viruses, so only virus-free certified budwood should be propagated on this rootstock.

G.202 produces trees slightly larger and more productive than M.26.

It is resistant to fire blight and wooly apple aphids and is tolerant of replant disease and crown and root rots.

It has good midwinter cold hardiness and produces few root suckers or burr knots.

G.202 has become very popular in New Zealand where growers are considering it to replace M.26.

G.222 is also in the same size category as M.26.

It is resistant to both wooly apply aphid and fire blight.

It is tolerant of crown rot, but not to replant disease.

Like the other Geneva rootstocks, it has very good cold hardiness.

Unfortunately, the rootstock does produce some root suckers and burr knots.

G.969 produces a tree between 45 and 55% the size of a standard, putting it in the same size category as M.7.

It is resistant to wooly apple aphid and fire blight and is tolerant of replant disease and crown rot.

It is also cold hardy and produces very few suckers and burr knots.

Due to its larger size, this rootstock is only recommended for use with very low vigor scion cultivars.

These are just some of the most commonly used rootstocks in high density training systems.

Every rootstock has its positive and negative attributes, and there is no perfect rootstock.

When deciding on what to order for your next planting, consider the field conditions at your planting site, your anticipated tree spacing, and what pest and disease issues you will be able to manage.

Remember that different cultivars may grow very differently on the same rootstock, so be sure to match with rootstock with each cultivar you plant.

Rootstock performance can be variable across different field sites, so it is important to trial a new rootstock on your site before establishing a large planting.

Also consider consulting with other growers in your area that might have a planting already established.

To learn more about these and other rootstocks, visit the Penn State Extension Tree Fruit Production website and consider purchasing a copy of the Pennsylvania Tree Fruit Production Guide.

NC-140 is a multi-state rootstock evaluation project and is an excellent resource for rootstock information.

If growing fruit trees is a new venture for you, gather as much information as possible prior to planting a new orchard and also consider taking a Penn State Extension course on commercial fruit growing.

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