34 Almond Facts
SEPTEMBER | OCTOBER 2014
Time To Consider
David Doll
Orchard Removal:
Preparation and Planning
Orchard removal and replanting is critical to almond
operations. Although the lifespan varies, at some point the
decision is made to remove the entire orchard and start
anew. The removal process should not be rushed, as care
must be taken to prevent cultural mistakes that will haunt the
new orchard for its 20+ years of existence.
Once the decision is made to replant an orchard, old trees
need to be removed. Trees are removed through the use of
tub grinders, by burning, or by wood cutting crews. Tub
grinding is the fastest method, but there can be a considerable
waitlist in some years. Small orchards or blocks (less than 15
acres) may be granted a burn permit, pending approval of the
local air resource board. Wood cutting crews take more time,
and stumps will still need to be removed and disposed.
After the trees in the orchard are removed, the feld needs
to be shallow ripped and spring-toothed to remove as many
of the old roots as possible. These roots harbor soilborne
diseases and pests, such as nematodes. Three or more
ripper passes are commonly made. In some instances, more
severe soil modifcation will be needed to overcome dense
subsurface soil layers. A backhoe can be used to dig pits to
determine the extent of limiting layers.
If plowpans, hardpans, or fragipans are observed, ripping
can help "shatter" these layers. In cases of clay lenses and
soil stratifcation, slip-plowing may be of beneft. The shank
needs to be 1.5 times deeper than the deepest limiting
layer. For example, if a hard pan is observed at 3-feet
deep, a ripper shank of 4.5-feet will be needed to shatter
the hardpan. Backhoeing is also an option and should be
considered in sandier soils. The complete mixing of the soil
profle by backhoeing promotes tree growth and increases
the effcacy of soil fumigant treatments in both new and
replanted orchards.
Research indicates that in some circumstances, however,
soil modifcation may not be as necessary as once thought.
In a comparative trial at the Nickels Soil Laboratory near
Arbuckle, CA, a microspinkler-irrigated almond orchard
that was pre-plant slip-plowed has not out yielded an un-
modifed, microsprinkler-irrigated control orchard. This lack
of difference is thought to be due to the use of a low volume
irrigation system (microsprinkler or drip), which provides the
ability to control water applications and the wetting profle
depth within the soil, minimizing the impact of soil saturation
occurring at the interface of soil layers. Orchards planned to
be fooded or irrigated with solid-set sprinklers (higher volume
irrigation systems) should still be modifed if a backhoe pit
analysis indicates the need. Modifcation on very shallow soils
(less than 2.5-feet to frst soil layer) is recommended.
Nematode Sampling and
Pre-Plant Management:
Nematode sampling is another important task before
replanting, but it can be tricky to get consistent results when
collecting samples. Samples should be taken once the soil
begins to cool in October. For best results, multiple soil
samples should be taken, with a minimum of one sample
per soil type present in the orchard. If soils are relatively
uniform, two to three samples should be made for felds
smaller than 60 acres. Five or six samples are needed for
larger uniform felds. A composite of fve to seven different
spots within the soil type or feld quadrant should be pooled
(mixed and combined) as one "sample." Soil samples should
be taken at a depth of 15-inches to 20-inches within the
rootzone of the tree. Once enough samples have been
collected, they should be placed in a properly labeled bag,
kept cool and out of the sun, and submitted to a lab to
conduct the nematode analysis. The University of California
Cooperative Extension has information online describing
sampling methods in more detail (www.fruitsandnuts.ucdavis.
edu/almondpages/almondorchardmanagement)
Ring, lesion, and rootknot nematodes are the major group of
species of concern in almond orchards. Historically, rootknot
nematode was a signifcant problem until resistant rootstocks
were developed. As the name suggests, rootknot nematode
causes galls or knots to form on the roots, leading to reduced
productivity and low vigor. Many — but not all — modern
rootstocks are resistant to rootknot nematode. Rootstocks
'Lovell,' 'Krymsk-86' and 'Paramount,' or 'GF677,' are
known to be susceptible to this devastating pest. Ring
nematodes, which are more common in sandy soils, can
cause severe stunting in almond trees as well as predispose
the tree to bacterial canker. There is no true resistance
to ring nematodes in current rootstocks, but 'Viking' and
'Lovell' appear to be the most tolerant.
Lesion nematodes are a particularly tiny type of nematode
found in all soil types. It causes stunting of trees that impacts
vigor and yield. Typically, trees with high inherent vigor are
able to "outgrow" the stunting caused by this nematode.
Therefore, more vigorous rootstocks (e.g. peach x almond
hybrids) tend to be more tolerant of lesion nematode.
If sampling reveals high counts of nematodes, soil
disturbance, cover-cropping or soil fumigation with
Editor’s Note: David Doll works as a tree nut farm advisor for the
University of California Cooperative Extension. He is based out of Merced
County. Since starting his job in 2008, David has been involved in many
aspects almond research including rootstocks, fumigant selection and use,
and young orchard development. He is looking forward to contributing
regularly as an author for this column, “Time to Consider.”