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ISSUE 6   JUNE 10, 1999

 

SMALL GRAIN DISEASE UPDATE

    Leaf rust was detected on winter wheat by Dr. Jim Miller, USDA Cereal Rust Pathologist,
Fargo, on June 3 in Carrington. Trace levels were found on the lower leaves of one variety. Dr. Yue Jin,
small grain pathologist at SDSU in Brookings, reports easily finding wheat leaf rust on lower leaves of
winter wheat varieties in the nursery located at Aurora, which is near Brookings, SD. These winter
wheat plots were in the mid-boot to early flowering stage. Yue Jin also reports that spring wheat in the
jointing stage at this SD site had a trace amount of leaf rust on the lower leaves, which he felt was
worrisome as the season has a long way to go for spring wheat. Yue Jin also observed some leaf rust
on rye, but he did not observe crown rust on oats nor did he observe any barley leaf rust. In southern
Kansas, most wheat has now lost its leaves due to leaf rust (Kansas Plant Disease Alert, June 7). Barley
yellow dwarf, tan spot, Septoria and Stagonospora also have taken a toll on Kansas wheat, according
to Bob Bowden, Kansas State Extension Plant Pathologist.

    On June 3 at Carrington, the winter wheat plots had considerable amount of tan spot infection
on the bottom and mid-leaves, but emerging flag leaves appeared still uninfected. A few lesions of Septoria
were also seen on winter wheat leaves., characterized by the dark fruiting bodies evident within the
necrotic lesion. Winter wheat is soon approaching the vulnerable stage for Fusarium head blight
(scab) infections, too.

    Tan spot infections also are showing on spring wheat where wheat stubble is present. Some
questions about early season application of Folicur for tan spot control have been received. The Section
18 for Folicur was granted for Fusarium head blight control. Although the Sec. 18 label also mentions
control of leaf diseases, the Section 18 allows Folicur to be applied only once, with a maximum
of 4 fl oz/acre. If a producer wishes to achieve early season tan spot control, Tilt fungicide and the
mancozebs are labeled specifically for this use.

Marcia McMullen
Extension Plant Pathologist/IPM Coordinator
email: mmcmulle@ndsuext.nodak.edu

 

NEW SMALL GRAIN DISEASE FORECASTING SYSTEM

    A disease forecasting system for wheat and barley growers will be newly available in North
Dakota and western Minnesota this year. Fusarium head blight (scab), tan spot, and Stagonospora
(Septoria) blight occurrence will be forecast during critical crop growth stages. Air samples of pathogens
in 17 locations will be combined with NDAWN weather data to provide localized forecasts. Locations
in the Red River Valley include Fargo, Prosper, Hillsboro, Northwood, Forest River, Cavalier, Humboldt,
Warren, Stephen, Eldred and Felton. Other locations in North Dakota are Langdon, Cando, Baker,
Bottineau, Mohall and Minot.

    Information will be available through a toll-free recorded message and a web page. Anyone in
North Dakota and Minnesota can call 1-888-248-7357 to get a brief message about the latest Fusarium
spore counts for each locality. More complete information is available at:

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

including links to weather forecasts, Extension Bulletins and current pest information. Forecasts for leaf
diseases should be updated every day while scab updates for most locations are expected to occur three
times a week. If they wish, local news media may use these sources in preparing their reports.

    Please be advised that this first year is a trial run for system deployment. A lot of problems have
arisen during the implementation phase and more are anticipated during system operation. We plan a
thorough evaluation of system effectiveness and appreciate any feedback you may have. Please see the
web page for a list of contributors to this project.

Dr. Len Francl
Department of Plant Pathology
voice: 701-231-7079
fax 701-231-7851

 

POTATO LATE BLIGHT HOTLINE
TOLL FREE NUMBER

    The toll-free number for the Potato Late Blight Hotline is 1-888-482-7286. It is up and running, and
can be accessed nation wide. The hotline can also be accessed nationwide using the toll number cited in
last week’s Crop and Pest Report as well as by using the Web site cited last week.

 

EMINENT USE ON SUGARBEET

    Recently Sip Cam Agro, the manufacturer of Eminent, provided detailed information on their new
product. Eminent has a section 18 in North Dakota and Minnesota for control of Cercospora leafspot.

    Mode of Action. Eminent is a sterol inhibitor, in the same class of chemistry and with the same
mode of action as Tilt and Folicur. This class of fungicide inhibits the growth of higher fungi by
preventing C14 demethylation, which is an essential step in ergosterol synthesis. Ergosterol is an
essential building block in the cell wall of higher fungi. Lower fungi, such as Pythium and Phytophthora
(includes the potato late blight fungus) do not use ergosterol in the formation of the cell wall, and so
their growth is not inhibited by this class of fungicide.

    Systemicity. Eminent is locally systemic, i.e. it is taken up by the leaf and moves within the leaf.
Uptake is slightly slower than that of Folicur, with 15% uptake in 2 days.

    Application. Eminent should be applied in 20-150 gal/A with ground equipment, or 5-10 gal/A by
air or concentrated spray ground equipment. Penetration into the canopy and down to the crown
(see below) is essential, so that every effort should be taken to assure adequate coverage, including
coverage of the crown. No spreader-sticker is required. The label rate is 13 fl oz/A, which is 0.1 lb ai/A.

    Resistance Management. The label states that Eminent should be applied at 14-21 day intervals. Data
from Europe indicate that Eminent provides good control on a 21 day interval if disease pressure is light to
moderate. However, Sip Cam is recommending a 14 day interval, as indicated below. Growers should
keep in mind that disease pressure was very high last year, as discussed in winter grower meetings, and
that disease pressure is liable to be high again this year if weather conditions are favorable for Cercospora.
A 14 day interval certainly should be observed in the southern Red River Valley, and probably also in the
central Red River Valley.

    Sip Cam recommends that Eminent be alternated with a different class of fungicide for resistance
management. This also was emphasized at the winter grower meetings. All currently registered sugarbeet
fungicides are of a different class from Eminent. Alternation with a tin fungicide would be one approach
to alternation of products.

    Sip Cam’s recommended application program is to start with Eminent, then apply 5 oz/A of a tin
fungicide 14 days later, followed by Eminent 10-14 days later, then 5 oz/A of a tin fungicide 14 days
later, with additional applications alternated in the same fashion as required. Sip Cam believes that starting
the program with Eminent is important since the early applications are important to disease control. In the
winter meetings we discussed the importance of not getting behind in fungicide applications and the
importance of alternating classes of fungicides. Starting with a strong fungicide makes sense.

    The manufacturers of tin products would prefer to start with tin since they believe that levels of tin
tolerance are lower at the start of the season. I suspect that this is the case, but we do not have definitive
data to support this yet. This topic is being addressed by a research project this summer. Starting with
Eminent for the first application should not increase levels of tin tolerance, however, and should provide
excellent early season disease control.

    Eminent could also be alternated with mancozeb. Research trials indicated that mancozeb provides
good control if it is used on a 7 day interval, but that it is less effective if used on a 10 day interval. If
mancozeb is applied, the next application of Eminent should be 7 days after the mancozeb. Benlate or
Topsin M may be used once. Since resistance to Benlate and Topsin M is widespread as far north as
Crookston and East Grand Forks, either product should be used only once, only in a tank mix
with mancozeb or tin (preferably mancozeb), and only early in the season. Eminent should follow a
Benlate or Topsin tank mix in 7-10 days.

    Other Considerations. With regard to rainfastness, Eminent is quite water soluble, but it has greater
affinity to the cuticle on the leaf. A light rain or dew may improve uptake. Once Eminent has dried on the
leaf for 2 hours, it should be well bound to the cuticle.

    The first application of Eminent is very critical. Good canopy penetration is important for complete
coverage and to get a good deposit on the crown. Eminent on the crown will stay there for weeks and
is available for uptake, with movement from the crown into new leaves.

    Information on tank mixes of Eminent with herbicides is limited. Sip Cam does not anticipate problems
with phytotoxicity in a tank mix, but little is known about the impact of a tank mix on the efficacy of herbicides
in that tank mix. Dr. Al Dexter will be conducting extensive trials this summer on Eminent-herbicide and
insecticide tank mixes.

 

DRY BEAN GROWER SURVEY SHOWS SOME MAJOR CHANGES IN
VARIETIES GROWN

    A survey of Northarvest dry bean growers recorded major changes in market classes and varieties
grown in 1998. Kidney beans, were the leading class of dry bean in Minnesota in 1998, planted
on 46% of Minnesota respondents’ acres, followed by pinto beans (22%) and navy beans (16%).
Kidney beans were the third most commonly planted class in Minnesota in 1997. Pinto beans were the
leading class in North Dakota in 1998, planted on 61% of respondents’ acres, followed by black beans
(17%) and navy beans (17%). In addition to the large increase in 1998 kidney bean plantings in Minnesota,
there was a large increase in black beans in North Dakota and a decrease in navy bean plantings in
both states.

    Norstar continued to be the leading navy bean grown, planted on 39% of Minnesota and 35% of North
Dakota respondents’ navy acres. There was a large increase of Mayflower navy beans in North Dakota,
planted on 25% of respondents’ navy acres. Montcalm dark red kidney continued to be the leading kidney
variety, planted on 78% of Minnesota respondents’ kidney acres.

    There were dramatic changes in pinto varieties grown in the past three years. Othello in North Dakota
and Topaz in Minnesota were the leading pinto varieties in both 1996 and 1997. In 1998 Maverick was
the leading variety in both states with 43% of the pinto acres, followed by Winchester (16%).

    In 1996 almost all pinto varieties grown were susceptible to rust, but by 1998 the rust resistant
varieties Maverick, Winchester, Remington and Chase accounted for 71% of the pinto acres planted
by Northarvest respondents.

    Use of rust fungicides dropped over these same years, with 36% of all respondents' acres sprayed
with a rust fungicide in 1996, 9% in 1997 and 4% in 1998. Although climatic changes may have been
partially responsible for reduced use of rust fungicides, the shift to varieties resistant to the prevalent rust
races likely played a major role in the reduced use of rust fungicides.

 

SURVEY REFLECTS CHANGE IN DRY BEAN DISEASE PROBLEMS IN 1998

    A survey of Northarvest dry bean growers reflected changes in dry bean disease problems in
1998, compared to 1996 and 1997. White mold, which was the worst disease problem on 70% of
respondents' acres in 1996 and 62% in 1997, was the worst disease problem on 42% in 1998. In
some areas wet weather ceased about the time that flowering began, substantially reducing the white
mold threat. This is reflected by a reduction in the use of white mold fungicides. They were used on
27% of respondents' acres in 1996, 34% in 1997 and on 23% in 1998. In 1996 and 1997 white
mold was the worst disease problem in both Minnesota and North Dakota.

    In 1998, however, root rot was the worst disease problem in Minnesota, as reported on 46%
of Minnesota respondents' acres, followed by white mold (28%). White mold was still the worst disease
in North Dakota, as reported on 48% of North dakota respondents’ acres. Root rot was recognized
as a much more serious disease problem in 1998 than in any previous year. Current NDSU/University
of Minnesota research on developing root rot resistant varieties and University of Minnesota research
on root rot biology and disease management including biological control promises to help reduce future
root rot losses.

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

 

PLANT DIAGNOSTIC LAB REPORT

    The pace is definitely picking up in the lab. Root rots, chemical injury, more manifestations of
environmental injury on trees, and some leaf spot diseases are the predominate types of samples.

    One of the more dramatic diseases seen this year is rust on buckthorn. This rust was first observed
during the latter part of May, but the spore stage present at that time was less obvious. Like many rust
diseases, there are two hosts and five spore stages required to complete the life cycle of the pathogen,
Puccinia coronata. The life cycle of buckthorn rust, more commonly known as crown rust of oats, is
completed in two spores that occur on the buckthorn and three spore stages that occur on oats, and
many other grass species. It is important to note that the economically important host is oat, but several
grass species also provide a host for the pathogen. These grass species are the means by which the
buckthorn, especially in the urban setting, are becoming infected.

    The most obvious spore stage, and the one that both Ron Smith, the NDSU Extension Horticulturist,
and I have received numerous calls on, is the aecial stage that occurs on the underside of the leaves of
buckthorn. Spores are produced in a structure known as an aecium, a whitish, tubular structure in which
are produced orange spores. These orange spores are very noticeable, readily rub off the leaf by now,
and are the spore that will subsequently infect oat and other grasses. It is one of the three spore stages
on oats and grasses that will infect the buckthorn again in the spring.

    On an otherwise healthy and established buckthorn, the rust infection, while unsightly, should not cause
long term damage to the plant. There are fungicides labeled for use against this rust as well. For the
homeowner, Bayleton 25 is labeled and for the greenhouse and nursery growers, Strike fungicide is available.

Cheryl Ruby
Plant Diagnostician
diaglab@ndsuext.nodak.edu


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