Pacific Northwest Vegetable Extension Group

of Washington State University, Oregon State University, and University of Idaho

Newsletter Archives

May 2002 Newsletter

Lindsey du Toit and Debra Inglis, editors
WSU Mount Vernon NWREC
16650 State Rte 536, Mount Vernon, WA 98273-4768
360-848-6140 (tel), 360-848-6159 (fax)

WSU Vegetable Pathology Team Newsletter

Welcome to the May 2002 edition of Washington State University's Vegetable Pathology Extension Team newsletter, the first edition of the 2002 growing season. This newsletter follows the team's May conference call when team members discussed current vegetable diseases occurring in the state, their diagnoses and control. If you have questions or comments regarding vegetable diseases or WSU's vegetable pathology team, contact Debbie Inglis ( or Lindsey du Toit (


What is Plant Health Progress?
Plant Health Progress is a new multi-disciplinary science-based journal covering all aspects of applied plant health management. Both peer-reviewed and fully citable, the journal is an online-only publication. Plant Health Progress is a not-for-profit collaborative endeavor of the plant health community at large, serving practitioners worldwide. Its primary goal is to provide a comprehensive one-stop Internet resource for plant health information. Plant Health Progress publishes articles on all aspects of plant health including abiotic disorders, diseases, insects, nematodes, weeds, integrated pest management and / or regulatory issues. To become a network subscriber, visit

New Disease Compendium Available
APS Press has now published the "Compendium of Diseases of Umbelliferous Crops" edited by R. M. Davis and R. N. Raid. The manual includes information about diseases of carrot, celery, cilantro, coriander, parsnip and other umbelliferous plants. To order call 1-800-328-7560 or view The cost is $49.

Learn to Manage Bedding Plants in Greenhouses
Information about the new bulletin, "Pest Management for Herb Bedding Plants Grown in the Greenhouse", published by the Universities of Connecticut and Massachusetts is available at

Need to Know More About Taking Digital Images?
Sending digital images sent to plant clinics can assist with the diagnosis of a plant disease (see our Aug 2001 newsletter, For further info on taking digital images, see

View New Edition of Sustainable Ag News
A new edition of the PNW Sustainable Agriculture Newsletter is available at It includes articles about mustard green manures and the new organic standards.

Proceedings Available
The Continuing Studies program at Simon Fraser University has announced that the proceedings from their workshop, "Food of the Future—Comparing Conventional, Organic and Genetically Modified Food Crops: Understanding and Managing the Risks" is now available at their web site,

Food Safety Farm to Table Conference
The Food Safety Farm to Table Conference will be held May 29–30 at the University Inn at Moscow, ID. The sessions will cover foodborne pathogens of special importance for high-risk groups, food biosecurity, food safety activities at WSU and UI, and food safety of ready-to-eat foods. For more information, view


Treating Seed for Disease Control
Spring, of course, is the time for planting. Many diseases of vegetables, caused by fungi bacteria or viruses, are carried in or on the seed. Disinfecting or treating seed to kill or suppress these organisms is important in controlling many vegetable diseases. One of the most common seed disinfecting methods is to soak seed in hot water (typically at temperatures around 120°F) for up to 20 minutes. However, this method needs to be tested in advance to make sure that it does not affect seed germination as vegetables, and even cultivars of the same species, differ in their sensitivity to injury by hot water treatments. Chemicals applied on the seed surface can also help protect seed and the developing seedling from decay or damping-off problems. In most cases, these materials are fungicidal in nature and help control diseases caused by plant pathogenic fungi. New biological seed treatments are also coming on the market for this purpose (see below). The PNW Plant Disease Management Handbook published by OSU, WSU and UI, gives the following instructions for treating seed:

  1. To treat small quantities of seed, use fungicides that are formulated as dusts. Shake seed and fungicide together, 3 to 5 minutes in a jar or can (not more than half full) with a tight-fitting lid. For small packets, add a pinch of dust to seed in the packet and shake well. For larger quantities of seed, use a rotary or mechanical mixer. Fungicide slurries often are more convenient for treating large amounts of seed.
  2. If the seeds you buy were treated by the seed dealer, do not treat them again.
  3. Most fungicides are either poisonous or noxious and must be handled with care. Follow manufacturer's label directions for handling. Avoid breathing excessive amounts of fumes. Use a mask if treating large quantities of seed. Do not feed treated seed to livestock. Do not permit children to have access to the fungicide or to treated seed

Seed treatments alone cannot be solely relied upon to control the diseases against which they are directed. Often a seed treatment is only one step in a series of disease control practices. Growers are usually encouraged to purchase and plant seed that has been tested to be pathogen-free. Cultural practices such as field sanitation, rotation, destroying weed carriers, and foliar sprays may also help to insure season-long disease control, especially since disease causing organisms can be found in places other than in or on seed i.e., old crop refuse in the seedbed, greenhouse or field, in soil, and on weeds.

An example of the role of seed treatments in management of vegetable diseases is well illustrated with the following two diseases of watermelon: 1) watermelon fruit blotch caused by the seed-borne bacterium Acidovorax avenae subsp. citrulli, and 2) damping-off of watermelon caused by several fungi including Pythium spp., Rhizoctonia solani, and Fusarium spp.

Photo of Acidovorax avenae subsp. citrulli on watermelon Photo of damping-off of watermelon

Acidovorax avenae subsp. citrulli, a seedborne bacterium, is the cause of watermelon fruit blotch. Photo courtesy of Mike Derie

Damping-off of watermelon caused by Rhizoctonia solani
Photo courtesy of Dr. Thomas Isakeit TAEX Weslaco, TX


Symptoms of watermelon fruit blotch begin on seedlings as small, water-soaked lesions on the underside of the cotyledons; lesions later become necrotic. In a greenhouse setting, a single infected plant in a tray can infect nearby plants, leading to epidemics after the seedlings are transplanted in a field. This disease is managed through planting seeds that have tested free of bacteria, managing watering practices/systems to minimize splash dispersal of the pathogen, spacing plants adequately for improved air circulation (particularly in greenhouse production of transplants), and foliar copper applications in the field.

Damping-off fungi are common soil-borne pathogens of many different vegetable seedlings and cause symptoms just prior to, or after, seedlings emerge from the soil. Decay or death of seeds or seedlings at the time of germination in soil, or sudden wilting, toppling over and rotting at the stem base of young seedlings that have emerged from soil, are the most common symptoms. Wet soil, high humidity, and cloudy days favor damping-off. In green-houses and seedbeds, damping-off fungi can be eradicated effectively from planting media by sterilization (e.g., steam, pasteurization, or fumigation). Use new flats or pots for planting, and disinfect old containers before using them again. When symptoms of damping-off first develop, allow the planting medium to dry out a little and provide as much air circulation and light penetration as possible. Many seed treatments are available for control of damping-off fungi. The specific fungicides registered will depend on the particular vegetable commodity. Commonly-used seed treatments include captan (broad-spectrum protectant fungicide), fludioxonil (e.g., Maxim, for pathogenic Fusarium, Rhizoctonia, and Alternaria spp.), thiram (broad-spectrum protectant fungicide), and metalaxyl or mefenoxam (e.g., Ridomil or Ridomil Gold for water molds such as Pythium and Phytophthora spp.). Copper drenches (e.g., C-O-C-S and tribasic copper sulfates) can be applied to many kinds of vegetables for control of post-emergent damping-off, but be aware of potential phytotoxicity problems with some vegetables. An increasing number of biological fungicides/bactericides are becoming available as seed treatments or for foliar applications. Refer to pp. 388-391 of the "2002 PNW Disease Management Handbook" for a relatively extensive list of biofungicides and plant activators, some of which are registered for use as seed treatments. To find the listing of seed treatment products registered in Washington, check the PICOL website at

Some common seedborne diseases on some vegetables in Washington.


Seedborne Pathogen




Fusarium oxysporum f. sp. asparagi
Fusarium proliferatum
Fusarium redolens

Fusarium root and crown rot

Treatment of both seed and crowns are recommended. Check the PICOL website*


Bean common mosaic virus (transmitted by seed and by aphids)

Bean common mosaic

Use virus-tested seed.

Pythium; Rhizoctonia solani

Damping-off and stem rot

Many seed treatments are available. Check the PICOL website*

Pseudomonas syringae
pv. phaseolicola and pv. syringae

Halo blight and brown spot

Plant bacteria-free seed.


Alternaria dauci

Alternaria radicina

Alternaria leaf spot and leaf blight

Black rot

Some seed treatments available. Check the PICOL website*

Use pathogen-free seed and transplants.

Xanthomonas hortorum pv. carotae

Bacterial leaf blight

Hot water seed treatments and the planting of bacteria-free seed is recommended.


Pythium spp. and Rhizoctonia spp.


Seed treatments are available. Check the PICOL website*


Pythium ultimum, Fusarium moniliforme, Fusarium spp., and Penicillium oxalicum (sweet corn)

Seed rot and seedling blight

Seed treatments are available. Check the PICOL website*

Sphacelotheca reiliana

Head smut

Seed treatments are available. Check the PICOL website*


Pythium ultimum
Rhizoctonia solani


Seed treatments are available. Check the PICOL website*

Lettuce mosaic virus (transmitted by seed and the green peach aphid)

Lettuce mosaic

Using virus-free seed is the best means of control

Phoma medicaginis var. pinodella
Ascochyta pisi
Mycosphaerella pinodes

Ascochyta blight (basal stem rot or black stem)

Use seed produced in disease-free fields.
Check the PICOL website*


Aspergillus niger

Black mold

For seed treatments, check the PICOL webstie*. Hot water seed treatments can be effective

Botrytis allii

Neck rot and bulb rot

For seed onions, use a seed treatment. Check the PICOL website*

Urocystis magica and
Urocystis colchici


Use a seed treatment. Check the PICOL website*


Pseudomonas syringae pv. pisi

Bacterial blight

For small seed lots, blight infested seed can be treated with house-hold bleach (10%) for 1 to 5 min; use disease-free seed.

Peronospora viciae

Downy mildew

Check the PICOL website*

Pea seedborne mosaic virus

Pea seedborne mosaic

Monitor principal or all seed lots for seedborne virus and destroy infected seed lots.

Pythium spp., Rhizoctonia solani, Thielaviopsis basicola, Phoma medicaginis var. pinodella

Seed rot and damping-off

Check the PICOL website*

*Check the PICOL website at for seed treatment products registered in Washington.

New Biological Seed Treatments for Vegetable Crops
Washington State Department of Agriculture has registered two new biological fungicide seed treatment products for use, Kodiak Flowable Biological Fungicide and Kodiak Vegetable FL Biological Fungicide. The crop uses include bean (dry), bean (green), bean (kidney), bean (lima), bean (navy), bean (pinto), and pea (green). On vegetables, Kodiak provides protection against Fusarium, Rhizoctonia, and other diseases. For further information, visit the Gustafson Inc., website,


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WSU Mount Vernon NWREC, 16650 State Route 536, Mount Vernon, WA 98273-4768, 360-848-6120
Contact Us: Lindsey du Toit and Carol Miles