Pacific Northwest Vegetable Extension Group

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

Newsletter Archives

August 2001 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 August 2001 edition of Washington State University's Vegetable Pathology Extension Team newsletter, the last edition of the 2001 growing season. This newsletter follows the team's August conference call when team members discussed current vegetable diseases, diagnoses and control. Please note that we will resume our growing season conference calls and newsletter activities next year. You will hear from us then. In the meantime, if you have questions or comments regarding vegetable diseases or the WSU vegetable pathology team, contact Debbie Inglis ( or Lindsey du Toit ( Also, view the vegetable pathology team website at

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Potato Tuber Rot Kits Are Available
The WSU-Mount Vernon Vegetable Pathology Program through the support of the Washington State Potato Commission is collecting potato tubers with symptoms of leak, pink rot, and/or late blight (see photos below). Our plan is to obtain isolates of Pythium, Phytophthora erythroseptica, and/or Phytophthora infestans from these samples, and test them for sensitivity to metalaxyl. Kits are available to send your tuber rot samples to us by express mail. Contact: or

Photo of leak of potato Photo of pink rot of potato Photo of late blight of potato
Pink rot
Late blight

Want to Know About Working with Resource-Poor Farmers to Manage Plant Diseases?
View the recent feature story on APSnet at:

School Starts Soon: K-12 Teacher Guides in Plant Pathology Are Available
View them at the APSnet web site: at:

Need Information about Integrated Pest Management?
The IPM Almanac (by GEMPLER'S) searches over 400 sites for IPM-related information

Request Made for Powdery Mildews
Dr. Dean Glawe, mycologist and director of WSU Research and Extension Centers and Units in western Washington, is doing research on the taxonomy, biology, and pathology of powdery mildew fungi. The samples will be used for a variety of research purposes and ultimately will be preserved in the Plant Pathology Department Mycological Herbarium--the largest mycological herbarium west of the Mississippi. Each sample should include 5-8 leaves of infected host plant material, preferably dried and pressed for a week before mailing, and should include the host plant name, the location of the collection site, the date collected, and the name of the collector. Please mail samples of powdery mildew on any garden, landscape or crop plant to the WSU-Puyallup Powdery Mildew Laboratory, 7612 Pioneer Way East, Puyallup, WA 98371-4998. Dr. Glawe hopes within the next several years to complete work on a guide to the powdery mildews of the Pacific Northwest, a publication that will be useful to field personnel, scientists, and homeowners. Your samples of fresh material will be critical to the success of this project! For more information contact

Image of cameraDigital Diagnosis (by Jenny Glass)

Have you been hearing a lot about digital diagnosis lately? Recently, digital plant samples have been submitted to the WSU Puyallup Plant and Insect Diagnostic Laboratory and to the WSU Vegetable Pathology Team to aid in diagnoses. The ability of plant pathologists, diagnosticians and other specialists to respond reliably to digital images and correctly answer associated questions depends on the type of information requested, the quality of the image, and the amount of information provided. Some images submitted for plant, fungal or insect identification have been fairly easy to identify (typically to the family or perhaps genus level). Other images, how-ever, have been more challenging. The diagnosis of plant problems via digital images is often not straightforward; the factors contributing to the problems can be complex and, thus, the process of diagnosis is complex. To ensure the most accurate diagnosis possible, digital images need to be accompanied by the same type of detailed information that accompanies plant samples submitted for diagnosis.

Use of digital images is becoming more common in the diagnostic process. Many plant samples sent to diagnostic laboratories are supplemented with digital images. These digital images have been useful to show features difficult to describe in words, such as field topography, distribution of the problem within the site or on the plant, and condition of surrounding plants.

Digital images have also been used regularly to improve communication about plant problems, thereby expanding networking capacity and exposure to diagnostic information for diagnosticians, specialists, agents and clients alike. Digital diagnosis can involve a variety of people/disciplines and expand the diagnostic "capability" of a particular lab. For example, when members of the WSU Vegetable Pathology team are unable to diagnose a mystery problem, they solicit assistance from others by sending e-mail messages containing digital images.

Several University diagnostic services across the county, including Texas A&M University (, the University of Georgia (, and the University of Florida (, offer digital diagnosis services. Most current systems are set up so that the responsibility of taking the digital images is in the hands of an extension agent (who has previously been trained to prepare clear and informative digital images). These digital images and the information about the problem are then e-mailed to the diagnostic laboratory where the diagnosis is made. The Texas Digital Diagnostic System webpage states that this type of digital diagnosis is "as easy as 1, 2, 3". Digital diagnosis can save valuable time and money, although users must have access to appropriate and often expensive equipment (including cameras and microscopes), and to adequate training in the proficient use of these resources.

Web pages promoting digital diagnostic services may not always provide information on the difficulties and drawbacks of digital diagnoses (including possible inaccurate diagnoses based on insufficient information). For a lively discussion on the merits and drawbacks of digital diagnosis, refer to the article "A Digital Disaster and the Ethics of Virtual Plant Pathology" and the corresponding letters on the American Phytopathological Society's online journal, Plant Health Progress, at (

Remember that digital diagnostic services cannot replace traditional methods of diagnosis. Rather, digital diagnosis provides an additional (and valuable) tool that can enhance existing diagnostic services, especially when used by teams of specialists. The most important aspect of any plant problem diagnosis, whether by traditional or digital means, is accuracy. Since digital diagnosis of plant health problems will likely become more common in the future, we need to think about how we can use digital images reliably and how such diagnostic efforts will fit into our programs. To begin with, most of us need to get better at taking digital images! Training sessions on the use of cameras and microscopes, and appropriate submission of digital samples, could be very helpful. In the meantime, here are some guidelines for preparing digital images:

  1. Take several images of the affected specimen and take comparison images of healthy tissue/plants.
  2. Take images from several different angles and several distances (close-up tissue and whole plant). One image usually is not sufficient for accurate diagnosis.
  3. For digital images taken through a microscope, the magnification of each image needs to be included.
  4. Take images that show distribution of the problem (whole field pictures, topography, associations), and where the problem is not occurring.
  5. Do not just focus just on an affected plant/plant part. Take images of nearby plants, weeds, etc. that may give the specialist additional information.
  6. View the pictures you take both in the field and on your computer before sending to the specialist/clinic. Some pictures may not be in focus and will not be worth sending.
  7. Always provide complete and extensive information about the problem and how the crop has been grown (symptoms, distribution, culture, soil type, etc.); just as you would for any plant sample submitted for diagnosis.
  8. Follow the digital sample with actual plant material sent to the diagnostic lab.

If you are interested in receiving training about preparing plant and microscope images for this type of diagnosis, please contact Jenny Glass at Based on the number of responses, the Vegetable Pathology Team may coordinate a training workshop.

News from the WSU-Puyallup Plant Clinic (by Jenny Glass)
The clinic has received some vegetable disease samples this summer including:

  • Edamame seed submitted to determine why a field germinated so poorly (Carol Miles saysthis is a perpetual problem with Edamame and is related to lipoxygenase levels which affect seed storability and germination)
  • tomatoes submitted with severe flea beetle damage; and, others with Botrytis cinerea attacking the stem, girdling the plant inducing the development of numerous adventitious roots
  • peas submitted with powdery mildew (Erysiphe pisi) where a heavy infestation affected an organic farm (run as a crop share operation)
  • pumpkins submitted with viral leaf symptoms as well as numerous aphids
  • collard greens submitted with downy mildew
  • tomatoes from home gardens with blossom end rot
  • discolored peppers from home gardens (probably due to lack of heat units).

For more information about the Puyallup Plant and Insect Diagnostic Laboratory, please see the web page ( ). This web page includes the host-pathogen indices for the past two years as well as information on how to submit samples to the clinic. For additional information or comments about the web site, please contact Jenny Glass ( Thanks.

Vegetable Diseases/Issues and Places to Find Information

Post-harvest diseases of vegetables
As the harvest season approaches, many vegetable growers and gardeners anxiously await the "fruit" of their labor. The term "vegetable" refers to a wide range of vegetative plant parts such as shoots (asparagus), leaves (lettuce), leaf stalks (celery), flower buds (artichokes), inflorescences (sprouting broccoli), seed pods (peas and beans), bulbs (onions), roots (carrots), tubers (potatoes), or rhizomes (ginger). But, some vegetables are (in the botanical sense) actually fruits. Tomatoes, peppers and eggplants in the Solanaceae, and cucumbers and squashes in the Cucurbitaceae are some examples. Other vegetables are (in the culinary sense) commonly thought to be fruits. For example, rhubarb, the succulent leaf stalk of the rhubarb plant, is often considered a fruit because it is used in desserts.

In the context of post-harvest physiology and managing post-harvest diseases, the difference between a vegetable and fruit is important. This is because the metabolic activity of a plant part is related to its biological function. Immature organs (such as flower buds and fleshy seeds) have high respiration rates after harvest, and they cannot be expected to remain fresh for very long. Storage organs (such as mature roots and tubers) may be kept in good condition for months because of their low respiration rate.

For the majority of post-harvest diseases, infections usually begin in the field. Thus, initiating disease management practices during the season is critical to limit disease spread during transit and storage. Some common post-harvest diseases encountered in our region:

Crop Disease and Pathogen Symptoms/Occurrence Management Options*
Bean Watery soft rot
Sclerotinia spp.
Lesions on pods are first water-soaked, then brownish, and finally covered with a dense white mold Manage for disease during the field season; crops are generally most susceptible during flowering, particularly if plants are wet; less bushy types are more likely to escape disease; refrigeration retards but does not halt mold development
Cauli-flower Alternaria rot
Common throughout the world, these fungi cause brown or black discoloration of the curds; spores are disseminated by wind and insects, and even slugs; heads may be disfigured at harvest and can undergo serious rotting Manage for disease during the field season; the fungi persist in crop debris and seed; crop rotation out of all types of crucifers and control of cruciferous weeds is desirable; decay in storage can proceed at low temperatures
Cucumbers and zucchini Bacterial spot
Circular, sunken, water-soaked spots occur on the fruit surface; the bacteria spread rapidly under warm moist conditions; slight blemishes at packing may result in rapid symptom development during transit Manage for disease during the field season; if harvested fruits show signs of infection they should be marketed without delay
Cucumbers and zucchini Cottony leak
Pythium spp.
Soft dark lesions develop on the fruit at blossom or stem-end; infected flesh undergoes rapid breakdown releasing liquid; growth of bright white mold ensues; decay spreads rapidly during transit with "nests" of moldy fruits exuding watery juices Manage for disease during the field season; good drainage in the field and pre-cooling of produce before shipping is important; fruits in contact with the ground are especially vul-nerable; infections may also occur via cut stems
Lettuce Anthracnose
Microdochium panattonianum
Leaf spots develop rapidly into yellowish/reddish lesions which may be angular in shape, although circular sunken lesions occur on the midribs; centers of the lesions may fall out giving a "shot-hole" appearance Manage for disease during the field season; practice crop rotation and control wild lettuce; avoid moving through the field when foliage is wet; late infections inevitably lead to symptoms during transit/sales
Onion Grey mold rot
Botrytis spp.
The fungus grows down the leaves to infect neck tissues; during transport and storage, progressive decay of infected bulbs is governed by temperature Manage for disease during the field season; remove bulbs from the field within 48 hr of topping to avoid infection of green neck tissues; thorough drying at 30°C can prevent establishment of the fungus in the fleshy scales

*For disease control recommendations, check with the 2001 PNW Plant Disease Management Handbook. Some of the above information comes from Color Atlas of Post-Harvest Diseases and Disorders of Fruits and Vegetables Vol. 2 by Anna L. Snowdon. 1992. CRC Press Inc.

image of peaRegister for the Upcoming Pea Fusarium Wilt Workshop

When: October 12, 2001 (Friday) from 8:30 am to 4:30 pm
Where: 343 Johnson Hall, Washington State University, Pullman, WA 99164
For: Pea breeders, pea seed company personnel, pea growers, and others interested in
Fusarium wilt resistance in pea
Purpose:  This hands-on workshop will provide training in the use of conventional plant screening techniques and new molecular methods for identifying resistance in pea to Races 1, 2 and 5 of Fusarium oxysporum f. sp. pisi.
Cost: $25.00 (for workshop materials); lunch NOT included
For more information: Dr. Clarice J. Coyne, Cool Season Food Legumes Curator, USDA/ARS Western Regional Plant Introduction Station, Washington State University-Pullman; or Dr. Debra Inglis, Vegetable Pathology Program, WSU-Mount Vernon,
- - - - - - - - - - - - - - -
To register: Please fill-out the following form and mail to:
WSU-Mount Vernon REU, 16650 State Route 536, Mount Vernon, WA 98273-4768 with a check for $25.00 made payable to WSU-Mount Vernon (to offset the costs of the Fusarium wilt workshop).

Name ________________________________ Affiliation _____________________________

Address _____________________________________________________________________

Telephone ________________ Fax ________________ E-mail _______________________

Purpose for attending the workshop: _______________________________________________


Upcoming Vegetable Events
Check out the Vegetable Pathology Team’s calender for other upcoming events:


Our pages provide links to external sites for the convenience of users. WSU Extension does not manage these external sites, nor does Extension review, control, or take responsibility for the content of these sites. These external sites do not implicitly or explicitly represent official positions and policies of WSU Extension.

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