UMass Extension Greenhouse Crops and Floriculture Program

Damping-Off of Bedding Plants and Vegetables

Rhizoctonia Damping-Off of Catharanthus Seedlings

Introduction

Damping-off is a disease of germinating seeds and seedlings caused primarily by fungi. Within days, hundreds or thousands of seedlings can become colonized resulting in plant losses and delayed planting or shipping. Healthy appearing plants selected from flats with damping-off may develop root rot or stem canker several weeks later. With some damping-off fungi, foliar blight may also occur. Pythium, Phytophthora, Rhizoctonia and Alternaria are fungi that commonly cause damping-off. There are many other species of fungi that occasionally cause this disease.

Symptoms

Fungi may attack germinating seeds or young seedlings. If poor plant emergence occurs, inspect the soil. If the seed has not germinated it may have been subjected to unfavorable environmental conditions or it may be old. If germination has occurred and the hypocotyl (emerging shoot) is water-soaked in appearance or visibly decayed, fungi are the most likely cause.

Seedlings often develop a darkened or shriveled "wire stem" appearance at the base of the stem. The top of the plant may appear healthy when it falls over but quickly wilts and dies. The roots may or may not be decayed. When seeds are germinated in flats or beds, the disease often occurs in a roughly circular pattern. This is because of the tendency of fungi to grow radially from the point of origin. If there is a lot of fungal contamination, a circular pattern will not be apparent. In plug trays, spread occurs by splashing irrigation water resulting in a more random distribution of disease. The plug cells inhibit the radial growth pattern seen in flats of soil.

Unfavorable environmental conditions and cultural practices can result in seedling death that resembles damping-off. Hot water from sun-baked pipes and hoses, over-fertilization, low temperatures, drought, heat stress and chemical injury can all kill seedlings. However, in most of these cases initial symptoms occur on the foliage or upper part of the seedlings. When the seedlings collapse, the stem at the soil line is usually firm and healthy and the root system is unaffected. An exception to this would be over-fertilization which usually causes roots to appear desiccated and shriveled.

Sources of fungi

Some fungi such as Alternaria are typically seed-borne rather than soil-borne. Alternaria may cause foliar blights on plants as well. Soil-borne fungi such as Pythium, Phytophthora, Rhizoctonia and Sclerotinia may be present in untreated or improperly treated field soil. While not impossible, it is unlikely that soil-less media are contaminated when purchased. However, these fungi can easily be transferred to the growth medium by soiled tools, hands, or hoses and splashing water from infested soil.

Management

Prevention is most important. Avoid contamination of the growing medium and purchase quality seed. Use a soil-less medium. Keep flats off of dirt floors. Hang up the hose ends. When disease occurs, have the cause determined. Drench the medium with a broad-spectrum fungicide or a mixture of fungicides.

When damping-off occurs in a flat, discard the entire flat. Healthy appearing plants may carry contaminated soil and may develop root rot or blight at a later date.

The fungicides listed below are registered for Damping-off and/or Root Rot of Bedding Plants and Vegetables

Fungicides for Pythium and Phytophthora

Common name Trade name Rate Comments *Crops

fosetyl-Al

 

Aliette® WDG

 

0.4 to 0.8 lb/100 gal; 2 pts/sq ft.

 

Drench; however, foliar applications of 2.5-5 lb/100 gal will control root rot of some plants.

 

Ornamentals

 

etridiazole

 

Truban® WP and EC, Terrazole 35WP and Terrazole L

 

See labels

 

Rates vary depending on the formulation. Irrigate immediately with additional water equal to at least half the volume of the fungicidal drench.

 

Ornamentals

 

mefenoxam

 

Subdue Maxx, Mefenoxam 2AQ

 

See labels

 

Rates vary depending on the plant. Subdue has broad crop clearance for ornamentals.

 

Ornamentals

 

dimethomorph

 

Stature

 

3.2-6.4 oz per 50-100 gal.

 

Apply when plant roots are well established on a 10-14 day interval. Use enough solution to wet root zone. Avoid irrigation for several hours before application.

 

Ornamentals

 

fluopicolide

 

Adorn

 

1.0 to 4.0 fl oz/100 gal

 

Must be tank mixed with another labeled fungicide with a different mode of action.

 

 

cyazofamid

 

Segway

 

1.5 to 3.0 fl oz/100 gal

 

Apply as a dench or to soil surface. Do no make more than two applications per crop cycle.

 

 

Potassium salts of phosphorous acid

 

Alude

 

6.25-12.75 fl oz/100 gal

 

Apply 25 gallons to 100 sq ft. Follow application with irrigation. Repeat as required. Limit to one application per month.

 

Ornamentals

 

thiophanate methyl plus etridiazole

 

Banrot® 8G

 

See label

 

Irrigate immediately with additional water equal to at least half the volume of the fungicidal drench. Also controls Rhizoctonia, Fusarium, Thielaviopsis and Cylindrocladium .

 

Ornamentals

 

fludioxonil plus mefenoxam

 

Hurricane

 

1.5 fl oz/100 gal

 

Applictions to Impatiens, New Guinea Impatiens, Geraniums, Pothos or Easter lily may cause chlorosis or stunting.

 

Ornamentals

 

propamocarb

 

Banol

 

2-3 fl oz/100 gal; see label for details.

 

Drench at 3 to 6 week intervals. May be tank mixed with thiophanate methyl for control of Rhizoctonia.

 

Ornamentals

 

Streptomyces griseovirdis

 

Mycostop

 

-------------

 

Suppression of Pythium that can cause seed, root and stem rot. Contains a beneficial bacterium. Repeat applications may be needed. Use as soil spray or drench. Acts as a preventative. Will not cure diseased plants.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Trichoderma virens

 

SoilGard

 

-------------

 

Contains a beneficial fungus. Acts as a preventative. Will not cure diseased plants. Do not use other soil fungicides with SoilGard at time of incorporation.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Trichoderma harzianum

 

RootShield

 

-------------

 

Contains a beneficial fungus. Avoid applications of fungicides a least one week before or after application. Acts as a preventative. Will not cure diseased plants.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Hydrogen dioxide

 

Oxidate, ZeroTol

 

---------------

 

Contact, oxidizing sanitizer.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Fungicides for Rhizoctonia

Common name Trade name Rate Comments *Crops

thiophanate methyl

 

Cleary's 3336
Fungo Flo
AllBan Flo
T-Storm

 

See labels

 

See label for seedlings and transplants. Cleary's has broad crop clearance for ornamentals. Use experimentally for plants not on the label. Rates vary depending on the formulation.

 

Ornamentals

 

iprodione

 

Sextant
26 GT
Chipco 26 GT
Iprodione Pro

 

See labels

 

See label for rates. Active primarily against Rhizoctonia . Apply 1 to 2 pints of solution per sq. ft. and repeat at 14 day intervals. Do not use as a drench on impatiens.

 

Ornamentals

 

iprodione plus thiophanate-methyl

 

26/36

 

13.5 fl oz/100 gal.

 

Do not apply as a drench to Impatiens or Pothos.

 

Ornamentals

 

PCNB

 

Terraclor® 75WP or 400F

 

4-8 oz/100 gal.

 

See labels for rates. Broad crop clearance for ornamentals. Active primarily against Rhizoctonia and Sclerotinia .

 

Ornamentals,
Vegetable Plants

 

thiophanate methyl plus chlorothalonil

 

Spectro 90 WDG

 

1.0 to 2.0 lb/100gal

 

See labels for specific instructions.

 

Ornamentals

 

thiophanate methyl plus etridiazole

 

Banrot® 40WP

 

see above

 

see above

 

see above

 

fludioxonil

 

Medallion

 

1 to 2 oz packets/100 gal.

 

For Rhizoctonia , apply sufficient water to wet the top half of the growing medium. For other pathogens, completely drench the growing medium. Medallion can be mixed with Subdue for broad spectrum control.

 

Ornamentals

 

triflumizole

 

Terraguard 50W

 

4-8 oz/100 gal; 4 fl oz/6 inch pot.

 

For best results do not irrigate with additional water until 24 hr after application. Apply at 3-4 week intervals as needed. Do not use on impatiens plugs. On impatiens transplants, do not exceed 2 oz/100 gal.

 

Ornamentals

 

azoxystrobin

 

Heritage

 

0.2-0.9 oz per 100 gal. 1-2 pt per sq ft at 7-28 day interval.

 

Do not make more than two sequential applications of Heritage. Do not rotate with Compass. Use caution applying to small bedding plants as phytotoxicity can occur.

 

Ornamentals

 

trifloxystrobin

 

Compass

 

0.5 to 1 oz per 100 gal. Drench to wet upper ½ of growing medium.

 

Active against Rhizoctonia, Cylindrocladium, and Phytophthora parasitica. Do not make than two sequential applications. Do not rotate with Heritage. Do not apply to vegetable transplants.

 

Ornamentals

 

flutolanil

 

Contrast

 

3 to 6 one oz packets/100 gal.

 

See label for volume of drench.

 

Ornamentals

 

pyraclostrobin plus boscalid

 

Pageant

 

8.0 to 12.0 oz/100 gal

 

Use caution when applying to Impatiens and petunia when flowering.

 

Ornamentals

 

Streptomyces griseovirdis

 

Mycostop

 

-------------

 

Suppression of Rhizoctonia that can cause seed, root and stem rot. Contains a beneficial bacterium. Repeat applications may be needed. Use as soil spray or drench. Acts as a preventative. Will not cure diseased plants.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Trichoderma virens

 

SoilGard

 

-------------

 

Contains a beneficial fungus. Acts as a preventative. Will not cure diseased plants. Do not use other soil fungicides with SoilGard at time of incorporation.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Trichoderma harzianum

 

RootShield

 

-------------

 

Contains a beneficial fungus. Avoid applications of fungicides a least one week before or after application. Acts as a preventative. Will not cure diseased plants.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Hydrogen dioxide

 

Oxidate, ZeroTol

 

---------------

 

Contact, oxidizing sanitizer.

 

Ornamentals,
Vegetable Plants,
Herbs

 

Key
*Crops: Crops registered for use.

See labels for rates and a complete explanation of precautions and restrictions.

Note: More than half of Pythium isolates cultured from greenhouse grown plants have been found to be resistant to Subdue Maxx. Do not use the same fungicide repeatedly, and rotate outside of a fungicide group.

1998 Prepared by Dr. Robert L. Wick, Department of Plant Pathology, Fernald Hall, University of Massachusetts, Amherst, MA 01003. Tel. (413) 545-1045 Fax (413) 454-2532

Tables revised 12/2013 by M. Bess Dicklow, UMass Extension Plant Diagnostic Lab

Links to Further Resources on the Web