SEPTEMBER | OCTOBER 2014
Almond Facts 35
Telone-II containing fumigants should be considered. Although exact
thresholds for nematodes have not been determined, I recommend pre-
plant fumigation if the average of counts from the feld samples for
ring, lesion, and rootknot are over 25, 50 and 50 nematodes per 500g of
soil, respectively. These approximate thresholds are lower if planting to
susceptible rootstocks (e.g. 'Lovell').
Cover cropping with non-host plants can help reduce nematode populations
as well as improve soil structure. Examples of non-host cover crops include:
true Sudangrass (not hybrid Sudangrass), barley, Merced Rye, Blando Brome,
and Salina Strawberry Clover. Soil disturbance through backhoeing of tree
sites appears to reduce populations in some trials. Broadcast fumigation
with Telone-II containing fumigants should be considered if populations are
especially high. Planting with resistant rootstocks is also recommended for
the felds with high soil nematode counts.
Prunus
Replant Disease and Management
Prunus Replant Disease (PRD) has been found in nearly every orchard
location that has had successive plantings of any Prunus species (peach,
Growth of an almond tree planted in C35
pre-plant-fumigated soil (left) compared to an
almond tree planted in unfumigated soil (right).
cherry, plum, almond, etc). This disease is
thought to be a complex of soil fungi that
reduce fne feeder root development, leading to
stunted growth and in severe cases, tree death.
Pre-plant soil fumigation, cover cropping and
soil modifcation appear to reduce the severity
of this disease. In multiple trials across the
state, fumigants containing chloropicrin have
outperformed the non-fumigated control. The
results have been the most favorable on sandy
loam or coarser soils. Research has not found
any comparable alternatives to fumigation, and
thus soil fumigation with chloropicrin containing
fumigants should be considered when back-to-
back plantings of any Prunus species is planned.
"The One-Two Punch"
In certain parts of California, orchards
replanted into ground with the presence of
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