Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines


  • Damping-off: Pythium spp., Rhizoctonia solani, and others
  • Symptoms and Signs

    Emerging 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 and oomycetes (fungus-like organisms). As the name implies, the disease is associated with damp conditions. Some Pythium species are favored by cool, wet conditions, but Rhizoctonia and other Pythium species can cause disease under drier and warmer conditions.


    Vigorous seedlings grown from the best seed 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, properly graded 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 REI‡
    (Example trade name) (hours)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
    (Mycostop)# 0.08 oz/lb 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. Suppresses also Botrytis, Pythium, and Phytophthora. May be used for both field-grown and greenhouse ornamentals.
    SOIL FUNGICIDE – Pythium spp.
    (Segway) 1.5–3.0 fl oz/100 gal water 12
    MODE OF ACTION GROUP NAME (NUMBER1): Quinone inside inhibitor (21)
    COMMENTS: Toxic to aquatic organisms.
    (Fenstop) 7–14 fl oz/50–100 gal water 12
    MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
    COMMENTS: Toxic to aquatic organisms.
    (Adorn) 1–4 fl oz/100 gal water 12
    MODE OF ACTION GROUP NAME (NUMBER1): Benzamides (43)
    COMMENTS: Toxic to aquatic organisms.
    (Subdue Maxx) Label rates 48
    MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
    COMMENTS: Applied at planting as a drench and periodically thereafter as needed. Available also in a granular formulation to use before planting. It is water-soluble and readily leached from soil. It is absorbed primarily through roots and is translocated in the plant through the xylem. Use of this material over a period of time may lead to resistance.
    SOIL FUNGICIDE – Rhizoctonia solani
    (Medallion WDG) Label rates 12
    MODE OF ACTION GROUP NAME (NUMBER1): Phenylpyrroles (12)
    (Chipco 26019 N/G) 6.5 oz/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
    (Prostar 70 WG) 3–6 oz/100 gal 12
    MODE OF ACTION GROUP NAME (NUMBER1): Succinate-dehydrogenase inhibitor (7)
    D. PCNB
    (Terraclor 400) Label rates 12
    MODE OF ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
    COMMENTS: Insoluble in water. Must be thoroughly mixed into the top 2 inches of soil to reach its desired depth of control. It works through vapor action and has good residual action. Germination of some seeds may be inhibited, and small plants may be stunted by this fungicide.
    (Talaris 4.5 F) 20 fl oz/100 gal for 800 sq ft bench area 12
    MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
    COMMENTS: Generally applied after sowing, as a drench or heavy spray. Thiophanate-methyl is absorbed by plant parts exposed to the chemical. Roots may absorb the fungicide (or its breakdown product carbendazim), which moves in the xylem to transpiring leaves.
    (TerraGuard SC) 4–8 fl 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 to 4 week intervals as needed.
    SOIL FUNGICIDE – Pythium spp. and Rhizoctonia solani
    (Pageant) 12–18 oz/100 gal 12
    MODE OF ACTION GROUP NAME (NUMBER1): Carboximide (7) and quinone outside inhibitor (11)
    (RootShield)# Label rates NA
    MODE OF ACTION GROUP NAME (NUMBER1): microbial (BM 02)
    COMMENTS: Formulated as a seed protectant, a soil drench, and as granules. 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. 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 (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.
    NA Not applicable.
    Text Updated: 11/20
    Treatment Table Updated: 11/20