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How to Manage Pests
UC Pest Management Guidelines
Plum
Phytophthora Root and Crown Rot
Pathogen: Phytophthora spp.
(Reviewed 5/06,
updated 4/09)
In this Guideline:
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Symptom expression depends upon how much of the root or crown
tissues are affected and how quickly they are destroyed. Generally, crown rots
advance rapidly and trees collapse and die soon after the first warm weather of
spring. Leaves of such tress wilt, dry, and remain attached to the tree.
Chronic infections, usually of the roots, cause reduction in growth and early
senescence and leaf fall. These trees may be unthrifty for several years before
succumbing to the disease. Phytophthora infections typically kill young trees
because their root systems and crown areas are small compared to those of
mature trees.
Periods of 24 hours or more of saturated soil favor Phytophthora
infections. Conversely, good soil drainage and more frequent but shorter
irrigations reduce the risk of root and crown rot. Rootstocks vary in susceptibility
to the different Phytophthora species;
none are resistant to all pathogenic species of the fungus. Thus, the success
of a rootstock may depend in part upon the species of Phytophthora present in the orchard. In general, plum rootstocks
are more resistant than are peach or apricot.
The most effective ways to manage Phytophthora root and crown rot
are to select a good planting site, select an appropriate rootstock, and
properly manage irrigation water. Avoid overirrigating in spring and fall when
soil temperatures are most conducive to disease development and water use by
the tree is low. Plum rootstocks are less susceptible to Phytophthora
infections than peach rootstocks, so plums grown on plum rootstock seldom have
this disease. Fungicides are also available to treat soil around newly planted
trees. If there is a history of Phytophthora root rot in the orchards and
problems are anticipated, treatments may be warranted.
| Common name |
Amount to Use |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
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(hours) |
(days) |
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| When choosing a pesticide, consider information relating
to environmental quality Not all registered pesticides are listed. Always read label of product being used. |
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| A. |
FOSETYL-AL |
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(Aliette) |
5 lb/100 gal |
12 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: For use on nonbearing trees only. Apply as a foliar spray at 60-day intervals. |
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| B. |
MEFENOXAM |
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(Ridomil Gold EC) |
Varies with method of |
48 |
0 |
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application and size of tree |
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MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4) |
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COMMENTS: Applications are made in early spring and fall. Do not apply to trees within 90 days of planting. |
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UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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