Tuesday, September 4, 2018

Failure to thrive

The in-ground portion of the rootstock is Bud 118.  This tree was planted in a site that previously hosted a peach tree.
I pulled an apple tree today.

It exhibited "failure to thrive" syndrome for the last two years.

Its siblings, same rootstock (Bud-118), interstem (G.935) and scion (Novaspy) are seven feet tall and show about thirty fruiting spurs each.  The terminal side shoots show an average of 24" of growth for the season.

The failure is about 40" tall.  The two highest terminal shoots died back.  The lower ones petered out after about 6".

The leaves showed symptoms similar to magnesium deficiency.  A foliar application of Epson Salts (magnesium sulfate) did not remedy the situation.

Today I ripped out the plant.

I found new young roots attempting to extend from the core root.  This is the opposite of a virtuous cycle.  The puny top growth does not produce enough carbohydrates for overwhelming root growth.

I found dead roots.  Lots of dead roots.  Dead roots are not very efficient at picking up nutrients or water.

And there were some live roots with what appear to be dead (necrotic) regions on them.
The potential culprits are nematodes, replant complex and Wooly Apple Aphids.
Results of greenhouse testing shows Bud-118 as having intermediate resistance to replant complex.  G-41 shows resistance to replant complex AND has good resistance to Wooly Apple Aphid.
Short of steam sterilizing or fumigating the ground, my best option is to not replant for a few years and then give it another go with something documented as being resistant to replant complex (a swirling mess of various pathogens that attack roots.)  As an added bonus there are also rootstock that are resistant to WAA, one of the other potential culprits.

I hope I removed Typhoid Mary before she had a chance to share with neighboring trees.

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