Pacific Northwest Vegetable Extension Group

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

Newsletter Archives

August 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 Aug 2002 edition of Washington State University's Vegetable Pathology Extension Team newsletter, the last edition of the 2002 growing season. This issue focuses on CARROTS, and we hope you enjoy it! Carrots are the most important source of beta carotene in the U.S. diet. In addition to beta carotene, the precursor of vitamin A, new "nutritionally improved carrots" now being tested by WSU contain one or more of several other plant pigments, such as xanthophyll, lycopene and anthocyanin that act as antioxidants and may help prevent heart disease and some forms of cancer. Pigment power in carrots may open a new a niche market for carrot growers, packers, and processors, and provide consumers with more colorful and health-promoting carrots.

Did you know that Washington's processing carrot growers are among the top producers in the nation? They grew 203,000 tons for the 1999 crop, which represents 35% of the U.S. total. Fresh market growers harvested 2,600 acres for the 1999 crop. Together, the value of production for fresh market and processing carrots was $31 million in Washington during 1999. For more information about carrots in Washington, look at the WSU Vegetable Pathology Team website at:

If you have questions or comments about carrot or other vegetable diseases or WSU's Vegetable Pathology Team, contact Debbie Inglis ( or Lindsey du Toit (


Photo of Cavity spot on carrots
Cavity spot on carrot caused by Pythium spp. (photo courtesy of Lindsey duToit).

Growers have reported problems with root diseases caused by Pythium and Rhizoctonia in some early-harvested carrot fields in the Columbia Basin. Generally, these problems follow periods with extremely high temperatures. Virus diseases are also showing up in some fields which border sagebrush land. Find out more about carrot diseases and their control in the table at the end of this newsletter.


2002 WSU Carrot Field Day Scheduled

You are invited to attend the 2002 WSU Carrot Cultivar Field Day! This year's event will feature 60+ lines of "nutritionally improved carrots" from the USDA carrot breeding program in Wisconsin, along with several commercially-available specialty carrots. The entries, which include dark-orange, yellow, red, and purple carrots, were planted for evaluation under local conditions on April 18. The field day will be an opportunity to observe these colorful new carrots, and discuss the carrot breeding program with Dr. Phil Simon, USDA carrot breeder, as well as meet with members of the Washington carrot industry.

The field day, which begins at 9:00 a.m., will be held at Klaustermeyer Farms on Aug 29. The field with the trial is located on Buffalo Lane, north of Hollingsworth Road and west of Buffalo Road. Everyone with an interest in carrot production and marketing is welcome to attend. Refreshments will be provided. For more information contact Erik Sorensen: tel- 509-545-3511, fax - 509-545-2130, or email – The carrot field day is sponsored by Washington State University Cooperative Extension, Benton-Franklin Counties, and the Pacific Northwest Vegetable Association.

Interested in Growing Carrots?
Information about growing carrots in Washington can be found within the Crop Profile for Carrots in Washington on the web at:

Additional information about growing carrots can be found in the Commercial Vegetable Production Guides from Oregon State University on the web at:

Washington State University publications about carrots can be found at:

Washington State University EB 1504, "Costs of Production: 2000 Carrot Enterprise Budgets, Columbia Basin", is now available on-line at:

Carrot Country
For regular information about issues concerning the U.S. carrot industry, you can subscribe to Carrot Country by contacting Columbia Publishing @ 509-248-2452 or by fax @ 509-248-4056. This magazine is a quarterly publication. The subscription fee is $8.

Carrot Research Projects in Washington...
Research projects on carrot diseases, pests, and other production issues are being carried out in the Columbia Basin by WSU faculty and extension agents:

1) Gary Pelter, WSU Extension Agent, has trials on weed control in carrot seed crops in the Columbia Basin.

2) Lindsey du Toit, WSU Vegetable Seed Pathologist, has a project on bacterial leaf blight (Xanthomonas campestris pv. carotae) on carrot seed crops, in collaboration with Fred Crowe, plant pathologist at OSU.

For further information about these projects, contact: Gary Pelter at 509-754-2011 ext. 314 or; or Lindsey duToit at 360-848-6140 or

Mark Your Calender Now
This year's Pacific Northwest Vegetable Association Conference will be held Nov. 21-22 in Pasco. The reporting session on carrots will be arranged for Nov. 22. For more information, contact Erik Sorensen (


Carrot Disease Compendium Available
APS Press now offers 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.

2001 Field Research Reports on Carrot Diseases
The 2002 volume of Fungicide and Nematicide Tests (results of 2001 published in 2002) includes four reports of field research done on carrots at various locations in the U.S. For access, see

1) Carroll, J. E., Ludwig, J. W., and Abawi, G. S. Evaluation of fungicides for control of leaf blight on carrot, 2002. Report No. 57:V018.

2) Langston, D. B. and J. E. Hudgins. Evaluations of fungicides and protection intervals for control of Alternaria leaf spot of carrot using two nitrogen fertility regimes, 2001. Report No. 57:V019.

3) Miller, M. E. and Hernandez, A. Evaluation of fungicides for powdery mildew control on carrot, 2001. Report No. 57: VO20.

4) Rogers, P. M., James, R. V., Stevenson, W. R., and Rand, R. E. Evaluation of fungicides to control carrot foliar blights, 2001. Report No. 57: V021.

In addition, the 2002 volume of Biological and Cultural Tests for Control of Plant Diseases (results of 2001 published in 2002) includes two reports of field research done on carrots. For access, see

1) Rogers, P. M., James, R. V., Stevenson, W. R., and Rand, R. E. Evaluation of carrot cultivars and breeding selections to identify resistance to foliar blights - Lewiston, 2001. Report No. 17:V09.

2) Rogers, P. M., James, R. V., Stevenson, W. R., and Rand, R. E. Evaluation of carrot cultivars and breeding selections to identify resistance to foliar blights - Hancock, 2001. Report No. 17:V08.

Photos of Carrot Diseases On-Line
WSU's Vegetable Pathology Team maintains a vegetable disease photo gallery which includes photos of diseases on carrots. Visit the site at:

Some Important Diseases on Carrot in Washington

Name Pathogen Important Features
Alternaria leaf spot and leaf blight Alternaria dauci

Hosts: one of the most common foliar diseases of carrot; can also affect parsley.
Favorable conditions: moderate to warm temperatures and prolonged periods of leaf wetness.
Symptoms: greenish brown, water-soaked lesions 8-10 days after infection. Once lesions coalesce, entire leaf may yellow, collapse and die. Petiole lesions kill entire leaves. Isolation of fungus often necessary for diagnosis.
Management: the fungus survives in seed, and for limited times in soil. Use pathogen-free seed, fungicide seed dressings or hot water seed treatments, crop rotation of at least 1 year, and plowing under of crop debris. Irrigate so that carrots are dry by nightfall. Foliar fungicides also can be applied preventively. For products registered in Washington, check

Aster yellows and BLTVA Aster yellows phytoplasma and beet leafhopper-transmitted virescence agent

Hosts: more than 300 species of plants affected. Aster yellows occurs worldwide but BLTVA has been reported in carrot only in the western U.S.
Favorable conditions: warmer winters that favor survival of the leafhopper vectors.
Symptoms: initial symptoms of aster yellows include yellowing of veins until entire leaf is chlorotic. Dormant buds in the crown beak and form upright, chlorotic adventitious shoots. Older leaves often turn red, purple or a bronze color. Carrot seed crops may show greening of the flowers and development of leaf-like flower petals. Symptoms of BLTVA include mild chlorosis and red or purple lower leaves. Taproots may be thin, woody, hairy.
Management: Aster yellows can be vectored by many species of leafhoppers. Leafhoppers acquire the phytoplasma from infected crops and weeds, and then transmit it in a persistent manner; they remain infected for life. BLTVA yellows is acquired and transmitted by the beet leafhopper. Control of both diseases includes removal of infected plants as soon as they are detected, elimination of weed reservoirs and planting away from infected crops.
Measures against leafhopper vectors have been effective in some areas.

Bacterial leaf blight Xanthomonas hortorum pv. carotae

Hosts: primarily carrot.
Favorable conditions: particularly important in areas with high rainfall or sprinkler-irrigation; also, warm temperatures.
Symptoms: initially appear as small yellow angular spots that expand to irregular brown water-soaked lesions surrounded by a yellow halo. Lesions are common at the "V" shaped junction of the leaflet lobes. On flower stalks, copious bacterial ooze may exude from elongated lesions. Blighting of umbels occurs in seed crops.
Management: since the bacterium is a common contaminant of carrot seed, the use of pathogen-free seed or hot water-treated seed is necessary. Copper-based bactericides can slow development of leaf blight in the field (check for Washington registrations). Use 2-3 yr crop rotations. Plow down refuse promptly after harvest.

Bacterial soft rot Erwinia carotovora subsp. carotovora, and Erwinia chrysanthemi

Hosts: common on many umbelliferous crops especially in storage; usually associated with wounds, freezing injury, insect openings, contaminated wash water or improper storage conditions.
Favorable conditions: 68-77°F for Ecc and 86-95°F for Ec; plant tissues deprived of oxygen (often occurring when soils become saturated) are particularly susceptible.
Symptoms: sunken dull orange-colored lesions on taproots, which collapse into a soft mass.
Management: These bacteria are ubiquitous. Avoid conditions which favor infection by allowing for good drainage, avoiding low areas in fields, allowing fields to dry between irrigations, avoiding plant injuries, and preventing contamination of harvesting and storage equipment.

Cavity spot, forking and stubbing Pythium spp.

Hosts: carrots primarily, although many asymptomatic hosts of some Pythium species are suspected.
Favorable conditions: factors which negatively affect carrot root health interact with various species of Pythium to cause these problems.
Symptoms: sunken elliptical lesions. Under the intact periderm the lesions are initially grey, but later when the periderm ruptures, they may become dark and elongated.
Management: numerous cultural practices can be helpful: avoid carrot production in fields with a history of cavity spot; plant seed in relatively warm soils with good drainage; avoid excess levels of fertilizer; do not delay harvest; practice long crop rotations of 3-4 years; apply metalaxyl ( for Washington registrations). Apparent failures of metalaxyl may be the result of rapid soil degradation of the fungicide in fields where metalaxyl has been used often.

Cottony rot or white mold Sclerotinia sclerotiorum

Hosts: one of the most common diseases of carrot crowns and roots, occurring also on many other crops such as beans, cabbage and cucurbits.
Favorable conditions: sclerotia of the fungus in soil produce fruiting bodies (apothecia) which can release millions of spores (ascospores) usually over a period of 2-3 weeks when temperatures range between 52-59°F.
Symptoms: the rot begins as small water-soaked lesions on crowns and roots; later, white mycelial mats develop on infected tissues which are further softened and decayed. These areas may be laced with the hard black resting structures (sclerotia) of the fungus.
Management: Can survive as sclerotia for up to 10 years. Diseased roots and stems in storage should be culled befoe shipping. Foliar fungicides are sometimes used in the field (check for Washington registrations). Cultural practices such as irrigation management, deep plowing, allowing air movement in the plant canopy, rotation with non-hosts such as cereal grains, grasses and onions, and rotation with broccoli or other green manure crops can be practiced. Ensure storage conditions of near-freezing temperatures and humidity of 85-90%. Carrots in bins rather than bulk piles have better air movement.

Motley dwarf Carrot mottle virus and carrot red leaf virus

Hosts: on carrot but also cilantro, dill and parsley.
Favorable conditions: when carrot is infected early during growth and temperatures are 59-68°F, losses can be severe. Above 75°F, infected carrots may be symptomless.
Symptoms: may vary with environmental conditions. Reddening and yellowing of leaves and overall stunting of leaves and roots may occur.
Management: Together, both viruses are transmitted plant-to-plant by the willow-carrot aphid. Old carrot plantings or overwintered infected carrots are generally the primary source of inoculum. Placing new carrot plantings away from inoculum sources and destroying volunteer carrots is effective for control.

Powdery mildew Erysiphe heraclei

Hosts: Many umbelliferous crops such as carrot, anise, caraway, chervil, coriander, dill, fennel, parsley and parsnip.
Favorable conditions: the spores do not require free water for germination, hence, conditions of high humidity and moderate temperatures favor infection and disease development. Sunlight may damage spores explaining why the disease can be more severe in the shade.
Symptoms: white mycelium and sporulation by the fungus may give a powdery appearance to all above-ground plant parts. Flowers may be distorted in seed carrot fields.
Management: Application of sulfur or other fungicides or biofungicides (check for Washington registrations). In addition, use tolerant cultivars, and avoid excess irrigation, shady growing conditions and water stress. Isolate new fields from established infected fields. 'Nantes and 'Imperator' types are more susceptible to the disease.

Root knot nematode Meloidogyne hapla

Hosts: root knot nematodes are distributed worldwide and occur on many crops species.
Favorable conditions: root knot is generally more severe in sandy-textured and muck soils than in clay soils. Damage to carrot is usually correlated to the size of the initial nematode population.
Symptoms: round to spindle-shaped swellings on feeder roots. Infected roots are usually short and have few lateral roots or root hairs. The galls may cause disfigured roots or root forking. Erratic plant stands, stunting, yellowing and wilting may result from loss of root vigor.
Management: Preplant soil fumigation when nematodes exceed economic threshold (2 per 100 cm3 soil in Washington). Check for Washington registrations. Crop rotation to nonhosts like corn or cereals, or long fallow.


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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