Newsletter Archives |
July 2003 Newsletter
Lindsey du Toit and Debra Inglis, editorsWSU 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
IN THIS ISSUE
- Hello
- Pest Alert (Early blight on potatoes)
- Upcoming Vegetable Events and Announcements
- Information About Controlling Vegetable Diseases & Pests
HELLO!
Welcome to the July 2003 edition of Washington State University's Vegetable Pathology Extension Team newsletter, the third edition of the 2003 growing season. We hope you will enjoy it. Be sure to view the excellent photos of carrot diseases at the end of the article!
If you have questions or comments about vegetable diseases and pests, or WSU's Vegetable Pathology Team, contact Debbie Inglis (dainglis@wsu.edu) or Lindsey du Toit (dutoit@wsu.edu).
PEST ALERT!!!
Growing conditions in western Washington have been unusually dry and hot. As a consequence potato and tomato growers have been irrigating their crops. Early blight, caused by Alternaria solani, is now being reported in some areas of western Washington. The weather is likely contributing to disease occurrences this year even though early blight is not often a serious problem in western Washington. Generally, early blight is found primarily under sprinkler irrigation; premature senescence resulting from drought or other stresses also favors disease development. Crop losses due to early blight can be significant if extensive foliar infections occur before or soon after flowering. Potato tubers and tomato fruits can also become infected. For information on cultural and chemical practices for controlling early blight, see the Pacific Northwest Plant Disease Management Handbook (bulletin@coopext.cahe.wsu.edu)
or contact dainglis@wsu.edu
Early blight lesions on potato leaflet. Note the dark colored "target" spots with surrounding chlorotic zones. Photo courtesy of Babette Gundersen. |
Early blight lesions on potato tuber. Note the circular sunken spots about 0.5 inch in diameter. The underlying tissue will be brown and corky. Photo courtesy of Gary Pelter. |
UPCOMING VEGETABLE EVENTS AND ANNOUNCEMENTS
2003 WSU Carrot Cultivar Field Day
The 2003 WSU Carrot Cultivar Field Day will be held on Friday, August
8th at 9 am at Klaustermeyer Farms in a field located near Othello,
WA. The event will feature a variety of carrot types including 17
slicers/cellos, 23 cut & peels, 12 dicers from commercial seed companies,
and 40 "nutritionally-improved" carrots from USDA breeders. The
field is located on Yeisley Road, east of Booker Road and south
of Highway 26 and north of Highway 17. For a map, contact Eric Sorensen
at esorensen@wsu.edu. The
field day is sponsored by WSU Extension, Benton-Franklin Counties,
and the Pacific Northwest Vegetable Association.
Onion Field
Day
The WSU Onion
Field Day is on Thursday August 28th at Grigg & Sons Farm near
Quincy, WA. The contact person is Gary Pelter peltegq@wsu.edu
or (509) 754-2011 ext. 413.
Potato Association
of America
The 87th Annual Meeting
of the Potato Association of America, "Back to Tradition", will
be held August 10-14 at the Red Lion Hotel at the Park in Spokane,
WA. For more information:
https://capps.wsu.edu/PAA2003/default.htm
WSU-Mount Vernon Potato Field Day and Cucumber Twilight Tour
The WSU-Mount Vernon Potato Field Day and Cucumber Twilight Tour
will be held Thursday, August 21 from 4 to 5:30 pm, and from 6:00
to 7:30 pm, respectively. For further information contact Debbie
Inglis at dainglis@wsu.edu
and Tim Miller at twmiller@wsu.edu.
INFORMATION ABOUT CONTROLLING VEGETABLE DISEASES & PESTS
The Washington State Department of Agriculture (WSDA) has a new
Web site address at https://agr.wa.gov/.
WSDA has designed the site to be more compatible with Web browsers
and user-friendly.
To view a listing of those who are doing plant disease diagnoses
for commercial plantings view WSU's online publication, "Analytical
Laboratories and Consultants Serving Ag in the PNW" at https://cru.cahe.wsu.edu/CEPublications/eb1578e/eb1578e.pdf
Commercial Vegetable Production Guides are available at https://oregonstate.edu/Dept/NWREC/vegindex.html.
Although written for Oregon commercial vegetable growers, they contain
a great deal of useful information. The guides were adapted by the
Oregon State University Extension Service from Oregon and Pacific
Northwest publications, publications of other public institutions,
published and unpublished research, and the professional experience
of OSU faculty and some colleagues in agribusiness.
A new title in organic pest management, Plant Protection Challenges
in Organic Production edited by D.M. Suckling and M.R. Butcher
can be ordered through the New Zealand Plant Protection Society.
Contact Lois.McKay@agresearch.co.nz
.
Other websites to check:
Certified Crop Advisor website: https://www.agronomy.org/cca
USDA Crop Profiles: https://www.reeusda.gov/pestmgt/successpdf/Crop%20profiles.pdf
Interregional Research Project (IR-4) Assists Growers of Minor Crops
https://www.reeusda.gov/pestmgt/successpdf/Interegional%20research.pdf
Carrot Seed Disease Management
Lindsey J. du Toit, WSU Vegetable Seed Pathology, Mount Vernon,
WA; and Gary Q. Pelter, WSU Cooperative Extension, Ephrata, WA
(Click here to go to the figures at the end of the article)
Three of the most important seedborne pathogens of carrot in the
Pacific Northwest are Alternaria dauci (the fungus causing
Alternaria leaf blight), Alternaria radicina (the fungus
causing black rot), and Xanthomonas campestris pv. carotae
(the bacterium causing bacterial leaf/umbel blight). Alternaria
leaf blight is seldom observed in Washington and, correspondingly,
Alternaria dauci is rarely detected on carrot seed produced
in the PNW. However, black rot and bacterial blight are observed
regularly, although sporadically, in carrot seed crops in the PNW;
and the associated pathogens, A. radicina and X. campestris
pv. carotae, have been detected on carrot seed lots produced
in this region.
What are the recommended practices for the carrot industry to manage
these seedborne pathogens?
1. The first step in effective regional management of seedborne
pathogens is to make it a routine practice to have all stock
seed lots tested for seedborne pathogens of concern in this region.
Seed testing should be completed prior to planting stock seed. However,
if circumstances prevent this (e.g., limited time from cleaning/shipping
of stock seed to planting), it is still valuable to have a sample
of the stock seed assayed after planting to identify the potential
risks of diseases developing as a result of seedborne inoculum.
This information will also help determine appropriate in-season
production and disease management practices needed. Only seed lots
determined to be free of seedborne pathogens should be used as stock
seed for organic seed crops.
2. If seedborne pathogens are detected on stock seed lots, infected
seed lots should be treated appropriately prior to planting
to reduce, or even eradicate, seedborne inoculum. Hot water, chlorine,
and fungicide seed treatments can be used. Fungicide seed treatments
do not eradicate seedborne inoculum, but prevent or reduce transmission
of some fungal pathogens from the seed to developing seedlings.
Not all fungicide seed treatments are effective against all seedborne
pathogens. For example, Rovral (iprodione) and Maxim (fludioxonil)
help prevent transmission of seedborne A. dauci and A.
radicina, but do little to control seedborne X. campestris
pv. carotae. Treatment of seed with chlorine alone will eradicate
inoculum located on the seed coat, but will not eradicate inoculum
located within the seed. However, hot water treatment can eradicate
internal seedborne inoculum when carried out precisely to allow
thorough penetration of the water (heated to a specific temperature)
into bags of seed for the specific duration determined for the seedborne
pathogens. For example, X. campestris pv. carotae
can be eradicated by placing infected seed in water heated to 125oF
(52oC) for 25 minutes. Alternaria radicina can eradicated
from carrot seed using hot water treatment at 122oF (50oC) for 30
minutes, or hot sodium hypochlorite (0.1 to 1.0%) at 122oF for 30
minutes. Treated seed should be re-assayed to determine whether
the pathogen was eradicated or the population decreased adequately
as a result of the treatment.
3. The initial disease management steps of assaying and treating
stock seed lots for pathogens also apply to steckling crops. Alternaria
radicina and X. campestris pv. carotae have been
detected on stecklings sampled directly out of shipping crates upon
arrival in Washington, highlighting the potential for stecklings
to serve as the initial source of inoculum. Stecklings should
be grown in areas where bacterial blight and black rot are less
prevalent, e.g., bacterial blight is widespread in the Central Valley
of CA, but seldom a problem in the Imperial Valley of CA. If there
is reason to suspect stecklings may be infected, the roots could
be dipped in a chlorine solution. Alternaria radicina can
continue to develop and spread from infected to healthy stecklings
during cold storage, so it is important to inspect stecklings for
evidence of black rot prior to cold storage.
4. Cultural management practices recommended for seedborne pathogens
apply to direct-seeded crops and to steckling beds. An adequate
crop rotation must be maintained. If a field has a record of A.
radicina infestation, a rotation interval of six years may not
be adequate since this pathogen has been shown to survive in soils
for up to eight years. In comparison, X. campestris pv. carotae
does not survive in the soil after carrot debris has decomposed.
Therefore, a minimum rotation interval of three years, combined
with incorporation of carrot residues into the soil immediately
after harvest (to speed up microbial degradation of the debris),
is recommended for management of bacterial blight.
5. In-field fungicide applications (e.g., Rovral, Kocide, etc.)
may be beneficial if black rot is present on the crowns/foliage.
However, foliar fungicide applications will not eradicate infection
established on roots beneath the soil-line. Development and spread
of bacterial blight can be minimized with foliar copper applications
(e.g., Kocide, C-O-C-S, or ManKocide), but the applications have
limited efficacy once bacterial blight is well established in a
seed crop.
6. The increase in use of overhead irrigation systems for carrot
seed production has particular ramifications for bacterial blight.
Wet foliage and splashing water are highly conducive to the spread
and development of bacterial blight. If a stock seed lot is infested
with X. campestris pv. carotae, grow the crop using
furrow or drip irrigation instead of overhead irrigation, to minimize
splash-dispersal of the pathogen. Similarly for stecklings infected
with bacterial blight. If a crop is under overhead irrigation, complete
each irrigation earlier in the day (where possible) to allow the
foliage to dry more rapidly compared to irrigating at night or later
in the day.
7. Volunteer carrots and related Umbelliferous weeds can serve as
reservoirs of carrot pathogens. Scout and rogue volunteers and related
weeds regularly, both within and adjacent to carrot seed crops.
8. Xanthomonas campestris pv. carotae has been detected
in airborne dust and debris generated during threshing, and as far
as a ½-mile from seed crops being threshed. Where possible, direct-seeded
crops should not be located immediately adjacent to mature crops
of the previous season, to minimize the risk of inoculum spreading
from the mature crop during threshing onto young seedlings of the
new crop. This recommendation is most pertinent when planting direct-seeded
crops 'early' (e.g., in early August in Washington), and when planting
direct-seeded crops under overhead irrigation.
Implementing appropriate production practices and management recommendations
will minimize the risk of introducing damaging carrot pathogens
in stock seed or stecklings, and will reduce the incidence of harvested
seed lots infected with these pathogens. Scout fields carefully
and regularly, and implement disease control measures immediately
when a pathogen is detected in a crop. Know the crop history before
determining the specific field in which to plant a carrot seed crop.
Fig. 1. Alternaria leaf blight caused by Alternaria dauci | |
Fig. 2. Spores of Alternaria dauci (100x magnification) |
|
Fig. 3. Black rot (crown rot) caused by Alternaria radicina. | |
Fig. 4. Foliar blight and crown rot caused by Alternaria radicina. | |
Fig. 5. Superficial russeting
of carrot stecklings caused by Alternaria radicina. |
|
Fig. 6. Spores of Alternaria radicina (55x magnification). | |
Fig. 7. Bacterial leaf blight with ooze caused by Xanthomonas campestris pv. carotae. |
|
Fig. 8. Umbel blight caused by Xanthomonas campestris pv. carotae. |
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