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UC Pest Management Guidelines


Damping off of spinach seedlings caused by Pythium.

Spinach

Damping-off and Root Rot

Pathogens: Fusarium oxysporum, Pythium species, and Rhizoctonia solani

(Reviewed 12/09, updated 12/09)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms of damping‑off and root rot consist of poor seed germination, preemergence death of seedlings, postemergence death of newly emerged seedlings, stunted plants, yellowed lower leaves, general poor growth, wilting, and eventual collapse and death of older plants. Roots of infected plants can appear water-soaked or brown to black in color. The upper taproot may be girdled by a necrotic lesion, or the tip of the taproot may be necrotic. In severe cases, nearly all roots may be girdled or rotted off.

COMMENTS ON THE DISEASE

Damping-off is problematic in spinach production areas throughout the world. Severity is influenced by cultivar, soil texture, irrigation, and pathogen populations. Severe damping-off is associated with clay or poorly draining soils with a history of frequent spinach production. While all stages of spinach can be infected by root rot organisms, newly emerging plants and young seedlings are very susceptible.

Symptomatic plants can be associated with low areas in the field and places where water is slow to drain away. These spinach problems are caused by a complex of pathogenic soil fungi that include one or more of the following: Fusarium oxysporum, Pythium (several species), and Rhizoctonia solani. These fungi are soil inhabitants and are therefore permanent residents in infested soils. However, aboveground symptoms of plants that are overwatered are similar to symptoms of root rot. Excess water can damage roots, causing tan to brown, water‑soaked symptoms on roots even if no pathogen is present.

MANAGEMENT

Plant spinach in well draining soils. Prepare seed beds so that even, rapid germination is enhanced. Carefully manage the irrigation schedule to prevent flooding and saturated soil conditions. Plant seed that is treated with fungicides. Preplant application of mefenoxam will only control damping-off caused by Pythium. Avoid planting consecutive spinach crops and practice good crop rotation.

Organically Acceptable Methods
Cultural controls such as good site location and preparation and good water management are acceptable for use on organically grown produce.

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 up to 1 lb a.i./acre/season for all formulations 48 21
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
  COMMENTS: There are several use recommendations that apply to all Ridomil formulations labeled for spinach. Do not exceed a total of 1.4 lb a.i./acre/growing season when using a combination of Ridomil Gold EC, Ridomil Gold GR, and Ridomil Gold/Copper. Plantback restrictions apply to some cereal grains and other food and feed crops. None of these products are registered for use in a greenhouse.
  (Ridomil Gold EC)   48 21
  COMMENTS: An emulsifiable concentrate registered for use in spinach as a soil application only. Applications may be made banded over the row, preplant incorporated, or injected with liquid fertilizer. Consult the label for specific application guidelines
  . . . or . . .
  (Ridomil Gold GR)   48 21
  COMMENTS: A granular formulation registered for use in spinach as a soil application only. Applications may be preplant incorporated or preemergence. Consult the label for specific application guidelines.
 
+ 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. 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: Spinach
UC ANR Publication 3467
Diseases
M. LeStrange, UC Cooperative Extension, Tulare County
S. T. Koike, UC Cooperative Extension, Monterey County

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