The Replant Test

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The biggest issue facing the apple industry in the Okanagan is low production. With proper management and horticultural support, our orchards are capable of producing at least 40 per cent more than they do. Production per acre has not increased in the past two decades and is well behind the per-acre production in Washington State.

The main problem lies in the poor preparations prior to replant and the failure of growers to apply the available technology to treat the decline that can result from poor replant management. Added to that is the failure of regulatory authorities to supply growers with the tools they need to sustain healthy trees in the face of constant threats from soil pathogens that are ubiquitous in tree fruit growing areas around the world.

Growers planning to replant this spring and growers with high density blocks that are under-producing need to consider their management strategies.

First step is to contact the B.C. Ministry extension specialist or your packinghouse field person for assistance before you attempt to replant. This is so important to the survival of your industry. There are plenty of technologies available to prevent replant problems and to treat decline before serious problems occur. Proper soil preparation in combination with correct spacing, good quality trees and proper subsequent management during the first year will eliminate years of poor growth and low production. Have a replant test done and make a plan.

Dr. John Slukhuis introduced the simple bioassay “replant test” in the early 1980s, and in a later publication (Apple Replant Disease, published in the APS Cpmpendium of Apple and Pear Disease), noted that it was clear from his research that soil fertility varied greatly from orchard block to orchard block.

The three plants on the left are controls (orchard soil with no amendments) and the plants on the right are in soil with phosphorus added. There is a 20 per cent increase in growth height and clearly larger healthier leaves when phosphorus was used in this soil.  Knowing this type of information before you plant rather than five years after you plant seems useful.

The test simply measures the growth of seedlings in untreated soil and soil with various modifications. There is a standard set of modifications such as addition of phosphorus (the correct form and application procedure being critical) fumigation (sterilization), soil amendments such as peat or compost, etc. The choice of treatments to be tested should include any “non-standard” soil amendment such as manure, soil replacement, etc., that a grower may be choosing to use in the planting area.

Once your soil has been assessed, using the replant test, the necessary modifications prior to planting can be made, making the production projections outlined in the early ministry production models possible. Without this information your planting success can be a crap shoot.

The biggest problems extension personnel have in making recommendations are:

1.A dependable replant testing facility has not been available;

2. Some orchard replants have been successful without any modification and the message gets disseminated that soil amendment (fumigation for example) isn’t necessary;

3. The impact of replant disease isn’t generally obvious (except in severe cases) until years four and five. By this time the problem is labelled as tree decline and not necessarily defined as a replant problem and there are no tools to deal with a serious decline situation.

The trees on the left are in the fall of the first year. They average about six-feet tall. In their second leaf they produced seven bins per acre. Those on the right are over five years old. They also average six feet, and likely produce no more than 20 bins per acre. The difference is in the root systems.

Once soil fertility has been assessed and soil preparation plans are in place, it is important to know and understand the subsequent management responsibilities required to keep the newly planted block on track for production numbers well above the industry average. This means minimum of 40 bins per acre of high quality fruit by year five.

The point is to monitor the soil before investing thousands of dollars in land preparation and tree costs. Mistakes are constantly made in tree spacing within the new plantings, which make attaining maximum production impossible. In these cases it becomes almost impossible to achieve production potential regardless of how well the orchard is managed.

Since the above technology has been known since the 1980s, why is it not utilized more widely?

The Okanagan Valley Tree Fruit Authority, responsible for implementing a very expensive replant program in the 1990s, failed to supply the field extension support growers needed.  The industries – including the BCFGA, the provincial government and the packinghouses – also have not shown the leadership needed.  With the know-how available there need not be replant failures and such low per acre production in the valley.

Replant tests can be arranged through the packinghouse laboratory in Winfield. Contact Dr. Danielle Hirkala at 250-766-2527.