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Phytophthora root rot may cause the xylem tissue of affected roots to turn yellow or brown.

Tomato

Phytophthora Root Rot

Pathogen: Phytophthora parasitica and P. capsici

(Reviewed 1/08, updated 1/08)

In this Guideline:


SYMPTOMS AND SIGNS

The most distinctive symptoms of Phytophthora root rot are the brown lesions on roots of all sizes. The xylem of the roots above the lesions often turns yellowish or brown in color. In severe cases, nearly all roots may be girdled or rotted off. Aboveground, infected plants are slow growing and may wilt or die in hot weather. When fruit in contact with the ground are infected, the disease is called buckeye rot. Symptoms include tan or brown spots with concentric rings. Phytophthora capsici also causes greasy, purple-brown stem lesions.

COMMENTS ON THE DISEASE

Phytophthora parasitica and P. capsici occur in most soils. Infection of plants occurs at any stage of growth when there is free water in the soil. Damage is greatest in poorly drained, compacted, or overirrigated soils.

MANAGEMENT

Good water management is key to managing this disease and avoiding the need for fungicide treatments.

Cultural Control
Provide good drainage and prevent flooding. Avoid wide fluctuations in soil moisture, which predisposes plants to infection. Keep tops of bed dry to avoid buckeye rot of the fruit. Planting cereals as a rotation crop may reduce the level of infestation in the soil. Resistant varieties are not yet commercially available.

Organically Acceptable Methods
Cultural control is acceptable in an organically certified crop.

Chemical Control
Fungicides are needed only in poorly drained soils or where root rot is historically a problem.

Common name Amount/Acre** R.E.I+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to environmental impact Not all registered pesticides are listed. Always read label of product being used.
 
A. MEFENOXAM
  (Ridomil Gold) EC 1 pt 48 28
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
  COMMENTS: Follow application with an irrigation (see label). Do not apply more than 3 pt/treated acre/season.
 
 
**  See label for dilution rate.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment until harvest can take place. In some cases the R.E.I. exceeds the P.H.I. The longer of these two intervals is the minimum time that must elapse before harvest may take place.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470
Diseases
R. M. Davis, Plant Pathology, UC Davis
G. Miyao, UC Cooperative Extension, Solano/Yolo counties
K. Subbarao, USDA Agricultural Research Station, Salinas
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the disease section:
B. W. Falk, Plant Pathology, UC Davis

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