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Tuber tissue rotted by Pythium has black margins and may be pink when first cut, turning gray and finally black with exposure to air.

Potato

Leak (Water Rot)

Pathogen: Pythium spp.

(Reviewed 8/07, updated 8/07)

In this Guideline:


SYMPTOMS AND SIGNS

Leak, also known as water rot, causes spongy, wet internal rot of tubers. The diseased flesh is clearly demarcated from healthy tissue by a dark boundary line. In advanced infections, hollow cavities form and all that remains of some infected tubers are tuber shells with thin papery skins.

COMMENTS ON THE DISEASE

The pathogen lives in the soil and enters through wounds made during harvest. The disease is primarily a problem in Kern County and causes the most damage when saturated soil occurs along with warm temperatures.

MANAGEMENT

Avoid overwatering near harvest. Allow tubers to mature completely before harvest. Minimize bruising the tubers. In areas where leak is a problem, treat 2 and 4 weeks before harvest.

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 the impact on environmental quality Not all registered pesticides are listed. Always read label of product being used.
 
A. MEFENOXAM/MANCOZEB
  (Ridomil Gold MZ) 2.5 lb 48 14
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)/Multi-site contact (M3)
  COMMENTS: Make the first application at flowering and another 14 days later.
 
B. MEFENOXAM/CHLOROTHALONIL
  (Ridomil Gold Bravo) 2 lb 48 14
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)/Multi-site contact (M5)
  COMMENTS: Make the first application at flowering and another 14 days later.
 
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 to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
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. For fungicides with mode of action Group numbers 1, 4, 9, 11, or 17, make no more than one application 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: Potato
UC ANR Publication 3463
Diseases
R. M. Davis, Plant Pathology, UC Davis
J. Nuñez, UC Cooperative Extension, Kern Co.
B. J. Aegerter, UC Cooperative Extension, San Joaquin Co.
Acknowledgment for contributions to the disease section:
C. Smart, Plant Pathology, UC Davis

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