WCN_Dec17WEB

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Replanting
When removing an aged orchard
for replant, Pope recommends a number
of steps especially when preparing
to replant that orchard into walnuts
again.
If removing an orchard for replant,
she said it is a good idea to plan for an
18-24 month transition between orchard
removal and planting new trees.
“Trying to rush the operation creates
several opportunities for a less satisfactory
outcome,” Pope said. “When replanting,
first figure out what carry-over
problems you’ll need to deal with from
the last orchard.”
This information can be used in
making decisions such as whether or
not to fumigate and with what product,
what to plant during the fallow period
and what rootstock to select for the
future orchard.
“There are a few problems that may
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Research and study have shown walnuts can
be successfully grown in marginal quality soil
when the soil is properly prepared for planting.
carry over from an old walnut orchard to
a new one planted on the same ground if
preventive or corrective steps are not taken,”
Pope said, “They are the walnut replant
problem, nematodes and crown gall.”
The walnut replant problem, sometimes
called the rejection component, is not
linked to one pathogen, she explains.
Carryover from a variety of biota from
the roots of mature walnut trees to new
trees can occur.
To avoid this carryover, Pope recommends
killing the roots of the old orchard
and rotating in a non-walnut crop for a
year.
The root-lesion nematode of concern
in California is Pratylenchus vulnus, Pope
said.
“Any previous tree crop planting is likely
to have hosted P. vulnus,” she added.
Pope recommends sampling for
nemotodes. Growers can see the UC IPM
Guidelines for sampling details at http://
ipm.ucanr.edu/PMG/r881200111.html, and
other nematode management information,
or speak with a laboratory which assesses
samples.
Crown gall, caused by the bacterium
Agrobacterium tumefaciens, once introduced
into an orchard or field site, has the
ability to survive for at least two years in
the orchard soil and at least one and a half
years in non-irrigated fallow soil, Pope
said.
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12 West Coast Nut December 2017