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How to Manage Pests
UC Pest Management Guidelines
Pistachio
Armillaria Root Rot (Oak Root Fungus)
Pathogen: Armillaria mellea
(Reviewed 2/07,
updated 2/07)
In this Guideline:
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SYMPTOMS
Roots infected with Armillaria mellea have white
to yellowish fan-shaped mycelial mats between the bark and the wood. Dark brown
to black rhizomorphs can
sometimes be seen on the root surface. Although pistachio is susceptible to
Armillaria root rot, the disease is infrequently reported. The relative
susceptibility of pistachio rootstocks is unknown.
COMMENTS ON THE DISEASE
The fungus survives on dead roots.
MANAGEMENT
Armillaria root rot is only occasionally a problem in pistachio orchards.
Management of this disease can be difficult and resistant rootstock may offer
the best protection. Research indicates that Pistacia terebinthus and P.
atlantica x P. integerrima hybrids are
tolerant but P. atlantica and P. integerrima are
susceptible. However, because pathogenicity and virulence in the natural
population of the pathogen ranges from weak to severe, disease response may
vary with different combinations of rootstocks and pathogen. Exposing an
infected crown may help individual trees with the disease. Soil fumigation as a
preplant treatment can slow progress of the disease, but eradication is not
likely.
Treatment Decisions
Before chemical treatment, remove all infected trees, stumps, and as many roots greater than 1
inch in diameter as possible. Healthy-appearing trees adjacent to those showing
symptoms are often infected also. Removal of these adjacent trees and inclusion
of that ground in the soil fumigation may be advisable. Infected trees, stumps,
and roots should be burned at the site or disposed of in areas where flood
waters cannot wash them to agricultural lands. Complete eradication is rarely
achieved, and retreatment may be necessary in localized areas. If the soil is
wet or if it has extensive clay layers to the depths reached by the roots,
fumigant treatment may not be successful. The greatest opportunity for
eradication occurs on shallow soils less than 5 feet in depth. Treat Armillaria
from late summer to early fall.
| Common name |
Amount/Acre |
R.E.I.+ |
| (trade name) |
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(hours) |
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| When
choosing a pesticide, consider information relating to environmental quality.
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| PREPLANT |
| A. |
METHYL BROMIDE* |
Label rates |
48 |
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COMMENTS:
Use permitted under a Critical Use Exemption permit only. Dry soil by withholding water during
summer and using cover crops such as sudangrass or safflower. The drier the
soil the better for deep penetration. Deep-till the area after drying. If the
soil is dusty, wait for an early rain before ripping and fumigation. Ripping
a dry soil that is silty can result in large clods on the surface. Inject
methyl bromide 18 to 30 inches deep with chisels and cover with gas-proof
cover. Increasing the dose tends to increase the depth of penetration, but it
cannot be relied upon to penetrate wet soils, especially if soils are high in
clay. Do not remove the cover for at least 2 weeks and aerate 1 month before
planting. Fumigants such as methyl bromide are a prime source of volatile
organic compounds (VOCs), which are a major air quality issue. Fumigate only
as a last resort when other management strategies have not been successful or are not available. |
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UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
Diseases
T. J. Michailides, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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