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ISSUE 2   May 13, 1999

PLANTING POTATOES AND BLACKLEG

    Blackleg and soft rot are bacterial diseases that can rot potato seed pieces or cause the lower stems
to become shiny black, with a wilting of the tops. Whenever the potato seed piece is covered with a film
of water, oxygen depletion occurs, establishing anaerobic conditions. This reduces the ability of the seed
piece to ward off infection, yet it has very little effect on the bacteria. These conditions favor the
development of soft rot and blackleg.

    Seed for planting should have less than 50% of the tubers infected with blackleg bacteria – the fewer
the better. Seed should be planted in well-drained soil with a planting depth soil temperature of 50-56F.
When planting seed into irrigated sands, the seed pieces should be allowed to warm up before planting,
as cold seed pieces tend to sweat if the sands warm up quickly after planting. When planting irrigated
potatoes, early or excessive irrigation should be avoided if possible, as this may lead to water accumulation
in low spots and the establishment of anaerobic conditions.

    Seed pieces should be treated with a recommended fungicide before planting to reduce Fusarium
dry rot, a disease that predisposes the potato plant to invasion by the blackleg bacterium.

 

STATE LABEL FOR RIDOMIL GOLD EC IN-FURROW APPLICATION TO POTATO

    A state label (SLN or 24c) was granted by the North Dakota Department of Agriculture for the use
of Ridomil Gold EC as an in-furrow application for suppression of pink rot and Pythium leak. Application
is to be made in a 6-8" band directly over the seed pieces at a rate of 0.42 fl oz/1,000 linear feet of row.

    Since the current US8 genotype of the late blight fungus is insensitive to Ridomil, application of Ridomil
when the tubers are forming no longer fits into a late blight spray program. NDSU research indicates that
the in-furrow application provides effective suppression of pink rot and Pythium leak at a cost effective price.

 

SECTION 18 GRANTED FOR EMINENT ON SUGARBEET

    EPA granted a section 18 for the use of Eminent (tetraconazole) on sugarbeet to control Cercospora
leaf spot of sugarbeet. Eminent is to be used at 13 fl oz/A. For purposes of resistance management,
Eminent should be used in alternation with a registered fungicide with a different mode of action (this
would apply to any currently registered fungicide). The fungicide following Eminent should be applied
14 days after the application of Eminent. Do not make more than 6 applications of Eminent per season
and do not apply within 14 days of harvest.

    Eminent has been tested for three years at various locations from southern Minnesota to Crookston,
Minnesota. It has always been one of the top performers at all locations in all years.

    There will be more on the use strategies of Eminent in future issues of this newsletter.

 

QUADRIS REGISTERED FOR POTATO

    Quadris received a full section 3 federal label about two months ago for control of late blight and
early blight. It is to be used at 6.2 fl oz/A on a 7 day interval for control of early blight or prevention
of late blight. It can also be applied at 12.4 fl oz/A on a 14 day interval for control of early blight.

    When late blight is active, Quadris should be applied at 12.4 -15.4 fl oz/A on a 5 day interval.

    For resistance management, Quadris should be alternated with a fungicide with a different mode
of action, such as Bravo. Do not make more than 6 applications and do not apply within 14 days
of harvest. Application of a spreader/sticker may improve coverage.

    In NDSU trials, Quadris provided excellent late blight control when applied at 12.4 fl oz/A. It also
provided excellent early blight control at the label rates cited above.

 

QUADRIS REGISTERED FOR CANOLA

    Quadris received a full section 3 federal label about two months ago for application to canola for
control of blackleg, Alternaria black spot and Sclerotinia stem rot.

    Sclerotinia stem rot has been a serious problem in recent years and canola producers have been
awaiting the registration of a fungicide. Blackleg and black spot have been sporadic in recent years;
both are more commonly a problem on Polish canola than on Argentine canola; the latter type is
most commonly grown in North Dakota.

    Blackleg. Quadris is to be applied at 6.2 fl oz/A at the 2-4 leaf stage for control of blackleg.

    Alternaria Black Spot. Quadris is to be applied at 8 fl oz/A at the pod stage (approximately
95% petal fall) for control of Alternaria black spot. Do not apply after 95% petal fall.

    Sclerotinia Stem Rot. Quadris is to be applied at 9.2-15.4 fl oz/A at 10-25% flowering (3-7 days
following first flower) for control of Sclerotinia stem rot. The proper application stage corresponds to
10-18 open flowers on the main stem of Argentine canola. Applications may be made by ground or air,
with no more than 3 applications per season.

    The 9.2 fl oz rate is to be used for light to moderate Sclerotinia pressure and the 15.4 fl oz rate is to
be used for heavy Sclerotinia pressure or when conditions favor Sclerotinia. Both rates were equally
effective in Kent McKay’s trial at Newberg in Bottineau County in 1998. Data from western Canada
trials indicates similar results from other locations.

    The 9.2 fl oz rate will cost over $21.00/A at currently projected prices. This is the cost for the
fungicide alone; not counting application costs. An economic return appears most likely if the yield
potential is at least 40 bu (2,000 lb), the weather has been wet for 10-14 days preceding flowering,
continued wet weather is expected, and Sclerotinia was known to be a problem in nearby fields in
the past one to three years.

    An extension publication on Sclerotinia stem rot and its management is in preparation, with targeted
publication in mid-June. This publication will include the Sclerotinia stem rot checklist developed in
Canada and published on the Canola Council of Canada’s Web site:  http://www.canola-council.org

    The permission of the Canola Council of Canada to duplicate this checklist, with permission, is
gratefully acknowledged.

Art Lamey
Extension Plant Pathologist
alamey@ndusext.nodak.edu

 

RECENT RAINS MAY FAVOR SEED ROT, SEEDLING BLIGHT

    Recent heavy rains in many areas have resulted in saturated or ponded soils. The condition of small
grains in these soils will be variable, depending on stage of crop development, depth of water, length
of exposure to ponding, and whether or not seed treatments were used. Seed treatments should
provide some protection from seed rot and seedling blight fungi for two to three weeks after planting.
Seed treatments aren’t going to provide much benefit if the crop is sitting under water for an extended
time, however. Long exposure to ponded water results in anaerobic conditions, with almost zero oxygen
available for a germinated plant that needs to respire. Cereal plants can take some short term (1-2 days)
ponding or flooding, as long as temperatures remain cool, but at higher temperatures, their survival rate
decreases. Decisions on replanting should not be made until the soil is dry enough to determine crop
condition.

 

EARLY SEASON TAN SPOT

    Early season tan spot on winter wheat has been reported by Tom Olson, Stutsman County Agent.
With the widespread rains, more tan spot should be showing up in the near future on any winter wheat
or spring wheat planted into wheat stubble. Under these conditions of wheat on wheat, and more than
adequate moisture available for the tan spot fungus to sporulate on wheat residue, growers should consider
the use of an early season fungicide for tan spot control.

    Early season fungicides, when warranted, are generally applied at the 4-5 leaf stage of spring wheat or
early tillering stage of winter wheat, and often are tank mixed with wheat herbicides applied at the same
time. If tank mixed with a herbicide, the herbicide label must be checked for any possible restrictions on
tank mixing.

    The two fungicides labeled for early season application for tan spot control in wheat are Tilt at the
2 fl oz rate, and the mancozebs, generally applied at the 1 lb/acre rate for early season control.

    The approximate cost of Tilt for the 2 fl oz/acre rate is $4.75/acre and one lb of mancozeb costs
about $2.75/acre. Recently, Rohm and Haas has developed an improved formulation of their mancozeb,
Dithane DF, and the new formulation is called Rain Shield. The manufacturer’s data indicates that
Dithane Rain Shield is substantially more resistant to run-off after one inch of rain than their old
formulation, which is good news for this class of protectant fungicides. I don’t know if there is a
price difference between Dithane DF and Dithane DF Rain Shield.

 

LATE SEEDED SMALL GRAINS AND BYDV

    Many small grains will be seeded later than optimum this year. The later the seeding, the higher risk
of wheat leaf rust and barley yellow dwarf virus (BYDV) infections. Last year, BYDV caught some
northeastern growers off-guard, as infection was severe on wheat planted late, around June 1. BYDV
is transmitted by grain aphids, and if aphid populations again build up to high numbers later in the
summer, late seeded grain could be at risk. One way we can control this disease is to use an insecticide
to control aphids, if needed. A web site is available that will help us keep track of aphid populations,
a site provided by Ted Radcliffe and the Univ. of Minnesota.

    The address is:  http://ipmworld.umn.edu/aphidalert/alert7.htm

    Some ND sites are included in the aphid study.

    Terry Gregoire, Extension Area Agronomist, recently spearheaded testing of some wheat varieties
for susceptibility to BYDV. Mike Edwards, USDA Virologist, Fargo, arranged for testing of the varieties
in the BYDV research greenhouse of Les Domier, USDA Virologist, Univ. of Illinois. Results of this
testing indicated that Russ, Hagar, 2375 and ACBarrie spring wheats had susceptibility to BYDV,
while Ben durum and Gunner, HJ98 and ACMajestic spring wheats had tolerance to the common
BYDV strain tested.

THREE SCAB WEB SITES

    Some excellent information on Fusarium head blight or scab is available on the web. In addition
to information available through the NDSU Extension site and the NDSU Plant Pathology web site,
an excellent article on scab is now featured on the American Phytopathology Society’s web site
at: http://www.scisoc.org/.

    Bob Stack, NDSU Plant Pathology Dept., wrote this feature article. Also accessible at this web
site is a previous feature article by Berlin Nelson, NDSU Plant Pathology Dept. Nelson’s article
features Stachybotrys chartarum: the Toxic Indoor Mold associated with flooded homes and
basements, perhaps once again a pertinent subject for our area.

    Another web site that has good information about the National Scab Initiative, as well as many,
many links to scab information, is:  http://www.scabusa.org/

    A third very good web site on this disease is from Canada
at: http://www.cgc.ca/Pubs/fusarium/fusarium-e2.htm

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu

 

PLANT DIAGNOSTIC LAB REPORT

    Many of the samples coming into the lab now are evergreens, spruce and pine, showing symptoms
of winter desiccation, other environmentally-induced disorders such as wet soils and high pH,
Rhizosphaera needlecast (Rhizosphaera kalkofii), and Cytospora canker (Cytospora kunzei).
Other tree diagnoses include transplant shock on apple and Oak Bullet Gall Wasp (Disholocaspis
quercusmamma
) on a Bur oak tree. Most of the remainder of the samples in the lab this year are
greenhouse produced plants. We saw a tomato with early blight (Alternaria solani), impatiens plant
infected with Impatiens Necrotic Spot Virus (INSV), petunia infected with Tobacco Mosaic virus (TMV),
and an assortment of greenhouse ornamentals showing symptoms of nutrient imbalance.

    Looking at plants to discern the cause for any problems, we often tend to focus on the green,
sometimes brown and dying, above ground parts; however the roots are just as important to the
health of the plant. The medium the roots are growing in, then, is also important. Soils across ND
vary a great deal within a field, or even within a homeowner’s yard. Site specific soil testing may be
necessary, if symptoms warrant, to determine nutrient disorders in plants. It is not appropriate to
assume that plants growing in different locations in a field, yard, or nursery setting are growing in a
homogenous soil if the soil came from a yard or field. To ensure a homogenous soil mix for greenhouse
or interior plants, it is important to thoroughly mix, consistently amend, and periodically test soils that
are used from fields. It is also true that soil microflora will vary within fields and yards. Certain
soilborne pathogens may be found in one area of a field or yard but not in another. It is not a good
practice to move infested soil or infected plant material to a new site that has not previously also been
known to be infested with soilborne organisms. Instead, plant non-host plants in an area infested with
a particular soilborne microorganism to deplete the population of that organism.

Cheryl Ruby
Plant Diagnostician
diaglab@ndsuext.nodak.edu


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