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ISSUE 10   JULY 8, 1999

 

SMALL GRAIN DISEASE SURVEY

    The following information was received from crop surveyors since the last Crop and Pest Report.
In the NorthCentral region of the state, tan spot is still the most common disease observed by Brittany
Sund. On the older crop, often 100% of the tillers show infection. Severities are still not high, but
infection levels are greater where wheat is planted back into wheat ground. Leaf rust has been
observed occasionally in this area, at trace severity levels. Brittany also observed some root rot in
several headed wheat fields.

    In the Southwest area of the state, Amy Dukart has frequently observed tan spot on wheat, Septoria
on wheat, spot blotch on barley, and bacterial spot on oats. She has observed wheat leaf rust fairly
commonly, but not at severe levels, and has observed loose smut in one wheat field at 10% incidence levels.

    In the Central and South Central districts, Jerry Schneider is finding leaf rust in most wheat fields,
with some fields showing several pustules also on the flag leaf. Tan spot and Septoria leaf diseases
also are starting to be apparent on the flag leaves of advanced wheat crops in these counties. Jerry also
has observed loose smut and barley yellow dwarf infections in a few fields. Several wheat fields in
LaMoure county had very high incidences of tillers with grain aphids.

    In eastern counties, Jerry Ries observed our first confirmation of wheat head scab - one infected
head in a Richland county field. We haven’t seen any other evidence of scab infection in spring grain yet.
Jerry has observed a gradual increase in levels of leaf rust, with some pustules on the flag leaves in
southeast counties, but levels remain very low in northeast counties surveyed. Jerry also has observed
quite a few fields in southeast and east central counties with the yellow tipped flag leaves, symptoms
characteristic of barley yellow dwarf virus infection.

 

THE LATEST FROM THE CEREAL DISEASE LAB, ST. PAUL

    The Cereal Rust Bulletin, dated July 6, 1999, indicates that wheat leaf rust severities on flag
leaves of susceptible winter wheat cultivars were high in central and eastern S. Dakota and in southern
Minnesota, during the last week of June. The bulletin states that "leaf rust is more severe and
concentrated in the Upper Midwest than it has been in the last 20 years." The Cereal Disease Lab also
reports wheat stem rust on susceptible winter wheats in Minnesota, South Dakota, Kansas and
Nebraska. Our commonly grown spring wheats and durums are resistant to stem rust, but a few winter
wheat cultivars, such as Norstar, are susceptible. Traces of crown rust of oats have been observed
in the oat nurseries at Fargo. Some leaf rust of barley was observed in west central Minnesota, as well.

 

DISEASE FORECASTING MODEL

    The disease forecasting model provided by Dr. Len Francl on the Internet indicated that for most weather
stations he is monitoring, this past week had very favorable infection periods for tan spot, and in many
cases, also for Septoria. Fusarium spore numbers were high at the Fargo research site on July 5, but only
two other locations (Stephen and Felton, MN) had any spores detected, and these were in low numbers on
that date. Fusarium development may have been favored during the past week and over the 4th of July
weekend, because of warm temperatures and very high humidities. Development would be retarded
by large drops in humidities and dew points.

 

CAUSES OF PREMATURELY WHITENED HEADS IN WHEAT

    With much of the early planted wheat already flowered and into grain fill, symptoms of whitened wheat
heads
may soon appear in some fields. Diseases, insects, or various stresses may cause these prematurely
whitened heads. With all of the saturated soils this spring, root rot may be a common culprit and cause
prematurely whitened plants and heads this year. The accompanying table describes many of the possible
causes of white heads, and ways to differentiate those causes. This table was adapted from a similar one
developed by Dr. Bob Bowden, Kansas State’s Extension Cereal Pathologist, which was printed in the
May 17, 1999 issue of the Kansas State Univ. Plant Disease Alert.


Possible Causes of White Wheat Heads

Malady

Stems and Leaves Remain Green?

All Tillers on Plant Affected?

Field Pattern

Other Diagnostic Features

Take-all root rot

No

Yes

Patchy

Roots and stem bases are shiny black

Common root rot

No

Yes

Patchy or random plants

Base of stem, crown, roots and subcrown internode are brown to dark brown

Fusarium foot rot

No

Yes

Patchy or random

Pink or white fungus inside crown or lower stem

Scab

Yes

No

Random or scattered

All or part of head turns white and has white or pink chalky grain

Stem maggot

Yes

No

Random

Heads pull out easily at first node; stem chewed off

Wheat stem sawfly

No

No

Patchy or random

Stem cut at base of plant

Drowning

No

Yes

Patchy

Low areas of field

Drought stress

No

Yes

Patchy

Plants stunted; especially on poor soils and upland areas of field

Hail

Yes

No

Random

Heads or stems broken, awns kinked

Frost injury

Yes

No

Random

Florets on all or part of head fail to develop to full size

Heat scorch or heat sterility

Yes

No (shorter tillers may escape damage)

Edge of field or patchy

Often occurs after extremely high temps, grain tips white and empty

Herbicide drift

Yes or No

No (shorter tillers may escape damage)

Edge of field often worse

Often worse downwind from row crops or stubble fields

 

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

 

WHITE MOLD CONTROL ON DRY BEANS

    Water Management on Irrigated Dry Beans. White mold is a serious problem on dry beans,
especially under irrigation. University of Minnesota trials at Staples, MN have demonstrated that
proper irrigation management is very important. In trials with plots that were irrigated when soil
water tension (SWT) reached either 30 cb or 65 cb, the best treatment in terms of disease management
and yield was irrigation when SWT reached 65 cb from planting throughout the season, with a yield
loss of just under 10% for unsprayed plots and about 2% for plots sprayed with a fungicide. A
treatment that was almost as good was irrigation when the SWT reached 65 cb from planting to
10 days into bloom, followed by irrigation when the SWT reached 30 cb for the rest of the season,
with losses of about 28% for the unsprayed and over 9% for plots sprayed with a fungicide.
Unsprayed plots irrigated when SWT reached 30 cb throughout the season sustained losses of
nearly 55%.

    Spray Decisions (Irrigated and Non-Irrigated). Other University of Minnesota trials measured
the total water (rainfall plus irrigation) that plots received from June 10 until 10 days into bloom (near
the end of July). When total water during this period was 3-5 inches, the use of a fungicide on pinto
beans was economic 20% of the time; when total water during this period was 5-7 inches, the use
of a fungicide on pinto beans was economic 65% of the time; and when total water during this period
was over 7 inches, the use of a fungicide on pinto beans was economic 85% of the time. Producers
can make these determinations on a field by field basis simply by using a rain gauge. Another handy
consideration is whether the soil is saturated as flowering begins; this concept is used in the Sclerotinia
risk map for canola.

    Reports indicate that some dry beans are flowering before the rows close. These plants may dry out
quicker, reducing white mold potential. However, plants could form a canopy quickly in warm, wet
weather, increasing white mold risk.

    Fungicides to Use. Benlate and Topsin M are registered for white mold control on dry beans. One
of the most economic and effective ways of using a fungicide is to use ground application with a directed
spray, a modification of what is thought of as a band spray. Drop nozzles are used between the rows,
and a nozzle is also used over the top. This provides maximum coverage of the entire plant, and is most
effective when nozzle pressures are 150 psi or more. The full rate should be used in the band, but if a 15
inch band is used on a 30 inch row, only half of each planted acre is sprayed, cutting fungicide costs in
half. This approach works well on 30 inch rows, but it is very difficult to use drop nozzles on 22 inch
rows; in this case it may be necessary to use a broadcast application. Use of broadcast air assist sprayers
has been as effective as use of drop nozzles on 30 inch rows; we have no data on their effectiveness on
22 inch rows. Aerial application also has been effective for white mold control. Use of 7-10 gal/A
appears more effective for aerial application of white mold fungicides than 5 gal/A.

    Timing of Fungicide Applications. Timing of white mold sprays is important. Data from Dr. Dick
Meronuck, University of Minnesota, has consistently shown that the best response from the use of
Benlate or Topsin M has been application at 4-10 days after the onset of bloom. I believe that the best
plan would be to apply 4-6 days after the onset of bloom; this would allow time to apply within the 10
day window if a rain delay were encountered at 4-6 days.

 

RUST CONTROL ON DRY BEANS

    Rust frequently shows up within 2 weeks of the first report of Cercospora leafspot on sugarbeet.
This would indicate that monitoring for rust should begin immediately. Rust is less of a threat than it
used to be, because many of the new pinto varieties are resistant to the prevailing races of rust in our
area. Fields planted to susceptible pinto varieties, as well to pinks or small red beans, should be
monitored routinely for rust. If two pustules are found before the lower pods are striping (have full sized
beans), or if one or two "hot spots" develop in a field, a fungicide should be applied. Bravo and maneb
are registered for bean rust control. Bravo gives 7-10 days of protection and maneb gives 5-7 days
of protection. Both are effective as protectant fungicides, but will not stop established infections.
Tilt has a section 18 emergency exemption in both North Dakota and Minnesota. Tilt is locally systemic,
provides 14 days of protection and can kill infections up to four days old.

 

SCLEROTINIA RISK ON CANOLA

    The Sclerotinia risk map on the Canola Council of Canada Web site shows severe risk across all
of southern Manitoba and southeastern Saskatchewan. This indicates that risk is high across the entire
northern tier of counties in North Dakota. Some canola has a good yield potential and an application
of Quadris might be cost effective in these fields. Farther south, producers will have to assess risk by
determining if their soils are saturated as flowering begins.

 

MORE CERCOSPORA ON SUGARBEET

    Cercospora leafspot was observed last week in the Crookston factory district. Warm, humid, rainy
weather during the past week has certainly favored Cercospora infections, especially in fields where
the crop has formed a canopy. Most fields in southern Minnesota, and many in the southern Red
River Valley have already been sprayed, and spraying should be under way in other areas. Many fields
in the extreme northern Red River Valley also are forming a canopy. Spraying should be initiated in
fields with a canopy, even if Cercospora has not yet appeared. This is a departure from what has
been said in past years, but we know that there is a huge carryover of Cercospora from last year,
and the disease has again showed up very early. These factors, in my opinion, require a preventive
spray so that fungicide is deposited on the lower leaves and in the crown while it is still possible to
reach these areas.

    There have been some questions about fungicide costs of Eminent versus the tin fungicides. I
believe that total costs (fungicide plus application), calculated on a per day basis, are similar for Eminent
and the tin fungicides. this is based on a recommended 5 oz rate of tin in the southern Red River Valley
and the use of a 10 day spray interval. Eminent should be used on a 14 day spray interval.

 

POTATO LATE BLIGHT AND EARLY BLIGHT

    The late blight hot line reports that late blight has been found in an irrigated field in central
Minnesota. The genotype is US-8, the same as in the past several seasons. Early blight has also
shown up in irrigated fields in Minnesota. Severity values at all irrigated weather stations in
North Dakota except Williston are well above the threshold. Several non-irrigated sites are
approaching threshold levels. Check the late blight hot line for details, including fungicide use
strategies.

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

 

PLANT DIAGNOSTIC LAB REPORT

    Beginning last season and continuing this year, the Plant Diagnostic Lab is accepting samples in
the form of a digital image. We have some things in place now to upgrade that system. The Plant
Diagnostic Lab web page is online, linked to the NDSU Extension Service page. The electronic link
is still in construction, but the URL for the diagnostic lab page is:

    http://www.ag.ndsu.nodak.edu/diaglab

    Digital images of insects or plants for identification, as well as plants for nutritional disorders, possible
disease, or any other concerns, can be taken with a digital camera, or scanned using a standard, flatbed
scanner. The next step is to fill out the electronic diagnostic lab form. Please be complete in the box
labeled additional comments so that we can specifically address your concerns and questions. At this
time, you cannot directly attach the images to the electronic sample submission form, but simply email
them with a message containing your name to the diagnostic lab. The cost of this type of sample submission
is the same as a visual diagnosis, $10.00 for a county agent, $15.00 for ND residents and $20.00 for
samples from any other state or country. There are drawbacks to this type of submission however, and
in the event that the digital image does not provide enough resolution or information to make a diagnosis,
we will notify you. You will not be charged for these samples, and would still have the opportunity to
send the physical sample to the lab. You may also supplement a physical sample with a digital image.
These images should be sent with the electronic sample submission form, including a comment with
regard to the specific sample the image supports.

    It is always best to set the camera to the highest resolution possible when taking digital pictures. For
plant identifications, lay out the leaves as flat as possible, showing both the upper and lower leaf surface.
Use small pieces of tape if necessary to get the parts to lay flat. Always include a common object or
ruler in the picture to provide a scale. For insects, take pictures from several angles to show all sides
of the insect. Detailed pictures of the eyes, mouth parts, antennae, or body parts will all help in the
diagnosis. For other types of diagnoses, try to take both whole plant pictures as well as detailed shots
of the lesions, spots, and/or distortions that indicate a problem.


Cheryl Ruby
Plant Diagnostician
diaglab@ndsuext.nodak.edu


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