Correcting blind wood in apples

Blind wood is a problem on some young apple trees.

Introduction

Blind wood is a problem on some young apple trees such as Fuji, Granny Smith, Jonagold and Honeycrisp. Blind wood can occur on the leader and laterals especially with high tree vigor and high apical dominance.  Paradormant buds are controlled by auxins flowing away from the shoot tips through the phloem downward in the plant. The auxins causes lower buds to remain dormant.

Notching and scoring is known to disrupt the auxin flow and free the paradorment buds to grow and develop. Cutting through the cambium just above a paradormant bud is called scoring and sometimes doesn’t work. Notching is a more aggressive form of scoring by removing a small amount of cambium just above the paradormant bud disrupting the flow in the cambium. This can be done by taping two hacksaw blades together and sawing out a small 3 mm strip just above the paradormant bud. A box-cutter knife makes a better notch by pressing the blade straight into the hardwood and then a second cut being brought down on a 45-degree angle to meet the straight cut and the angled notch being removed.

The old belief is that scoring and notching will break buds only on young wood for example: notching on 1-year-old will break about 90 percent, 2-year-old, 50 percent and 3-year-old, 10 percent, and no break will occur on 4+ older wood. But with the addition of PGR’s to the notch research has shown effect on paradormant buds on wood up to 7 years.  Be patience because it can take two to three extra weeks for the effect to show up.

PGR’s

Apply just a mist to the notch and do not flood the buds with excessive PGR mist. Treatment of notched wood with PGR’s, MaxCel and Promalin, proved to be the best combination to promote bud break and shoot extension. Numerous trials of various rates of these 2 PGR’s indicate that a mixture of 1500 ppm of MaxCel and 500 ppm Promalin with 1% v/v Regulaid seemed to work consistently with high success. The 6-BA in MaxCel encourages bud break and the gibberillins in the Promalin promote shoot extension. Together 90 percent will break buds and 80 percent will extend into and long shoot.

PGR Solution for 1 quart spray bottle

Just a mist, not a stream running down the tree.

Worked in cooler temperatures.

1500 ppm MaxCel

4.8 Tablespoons

500 ppm Promalin

1.6 Tablespoons

.25% v/v Regulaid

2.36 ml

Timing

The timing of this Notching+PGR treatment is best from green tip to tight cluster, but can be done 2 weeks before bud break to after full bloom. The sweet spot is at half inch green. Warm temperatures at that time will help increase the response of the PGR.

Risks

There are risks with this technique of Notching+PGR.

  • Fireblight. Be careful when considering notching during Fireblight conditions. Warm temperatures are the target for best PGR response, but this is when fireblight is also developing.
  • Flooding. Flooding out the notch can kill the bud. Apply just a mist of the solution to the notch.
  • Flooding with excessive runoff. Flooding out the notch and excessive runoff down the stem can crack the wood under the bud.

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