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UC Pest Management Guidelines


Bean seedling infected with Pythium.

Floriculture and Ornamental Nurseries

Damping-off

Pathogens: Rhizoctonia solani, Pythium spp., and others

(Reviewed 3/09, updated 3/09)

In this Guideline:


SYMPTOMS AND SIGNS

Seedlings rot at or below the soil line and are killed. Some seedlings may be infected before emergence and therefore not appear above ground. If the problem is caused by Pythium, it usually begins at the root tips. Damping-off pathogens can also infect planted seeds and cause death of the seed before it germinates.

COMMENTS ON THE DISEASE

Damping-off is the name given to seedling diseases most often caused by fungi. As the name implies, the disease is associated with damp conditions. Some Pythium species are favored by cool, wet conditions while Rhizoctonia can cause disease under somewhat drier and warmer conditions. ELISA test kits are available for detecting Pythium and Rhizoctonia pathogens.

MANAGEMENT

Vigorous seedlings grown from the best seed and under ideal light and temperature conditions may survive in the presence of these fungi while seedlings low in vigor will succumb under unfavorable conditions. Damping-off can be minimized by providing good drainage (raised beds, leveled fields), careful irrigation, planting when soil and air temperatures are favorable for rapid seedling emergence, proper depth and spacing of planting, seed treatments, and drenches of soil fungicides. For more information, see MANAGEMENT OF SOILBORNE PATHOGENS.

For container media, steam (at 140°F for 30 minutes) or solarize (double-tent at 160°F for 30 minutes or 140°F at 1 hour). For flower production in open fields, solarization in warmer climates has been successful for control of damping off in many crops. Reports of inadequate control of some high temperature species (e.g., P. aphanidermatum) have been made. Solarization and steaming are acceptable for organic production.

Common name Amount to Use R.E.I.+
(trade name)   (hours)

  Calculate impact of pesticide on air quality
When choosing a fungicide, consider the general properties of the fungicide as well as information relating to environmental impact.
 
SEED TREATMENT
A. STREPTOMYCES GRISEOVIRIDIS#
  (Mycostop) 0.08 oz/lb of seed or 5g/kg of seed 4
  COMMENTS: For control of seed rots, root and stem rots, and wilt diseases of ornamental crops caused by Alternaria, Fusarium, and Phomopsis; also suppresses Botrytis, Pythium, and Phytophthora. May be used for both field-grown and greenhouse ornamentals.
 
SOIL FUNGICIDE – Pythium spp.
A. MEFENOXAM
  (Subdue Maxx) Label rates 48
  MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
  COMMENTS: The granular formulation may be applied preplant or the liquid formulation can be applied as a drench at planting. Mefenoxam is water-soluble and readily leached from soil. It is absorbed primarily through roots and is translocated in the plant through the xylem.
 
SOIL FUNGICIDE – Rhizoctonia solani
A. IPRODIONE
  (Chipco 26019) 0.4 lb/100 gal water 12
  MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
  COMMENTS: Apply as a drench at seeding at the rate of 1–2 pt/sq ft
 
B. PCNB
  (Terraclor) 0.5–1 lb a.i./1000 sq ft 12
  MODE OF ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
  COMMENTS: Insoluable in water and must be thoroughly mixed into the top 2 inches of soil. Some seeds may be inhibited by this fungicide.
 
C. THIOPHANATE-METHYL
  (FungoFlo, etc.) 20 fl oz/100 gal for 800 sq ft bench area 12
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
 
D. TRIFLUMIZOLE
  (TerraGuard) 50W 4–8 oz/100 gal 12
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: For use in enclosed commercial structures only; less effective against Rhizoctonia than other materials. Apply as a soil drench at 3–4 week intervals as needed.
 
SOIL FUNGICIDE – Pythium spp. and Rhizoctonia solani
A. TRICHODERMA spp.#
  (Garden Solutions, Root Guardian) Label rates NA
  COMMENTS: Formulated as a seed treatment, a soil fungicide, and a nursery drench. This biological fungicide may provide some protection against both Pythium and Rhizoctonia.
 
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.
# Acceptable for use on organically grown ornamentals.
+ 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.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
S. T. Koike, UC Cooperative Extension Monterey County
C. A. Wilen, UC IPM Program, UC Cooperative Extension San Diego County
Acknowledgment for contributions to Diseases:
R. D. Raabe, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
A. H. McCain, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside

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