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Management
of annual weeds following wheat harvest
Jim Kells and Kathrin Schirmacher
Crop & Soil Sciences
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Annual weed densities are very high in wheat stubble
this year. These weeds must be managed soon in order to prevent
seed production. Several effective options are available for management
of annual weeds in wheat stubble. However, these practices must
be implemented before seed production to avoid significant additions
of seeds to the weed seed bank.
After wheat harvest, weeds take advantage of available
resources, especially newfound sunlight, and will grow rapidly,
especially in years with adequate soil moisture in July and August.
These weeds are capable of producing large amounts of seed prior
to a killing frost.
Common ragweed, velvetleaf, common lambsquarters,
redroot pigweed, and foxtail species are examples of common summer
annual weeds in wheat stubble. At this time of the year these weeds
are completing their life cycles by flowering and producing seed.
The main goal following wheat harvest is to prevent or reduce weed
seed production. Post-harvest weed control options include tillage,
mowing, and herbicides. In general, management of annual weeds in
wheat stubble is not difficult, however timeliness is critical.
Tillage is a viable option for control of both
broadleaf and grass weeds. Mowing will reduce seed production of
most grass and broadleaf weeds. However, mowing is often less effective
on grasses since seeds can be produced on tillers low on the plant.
Glyphosate and 2,4-D are common herbicides used for post-harvest
weed management in wheat stubble. Refer to the herbicide labels
for appropriate rates, adjuvants, and tank mixes.
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Do you suspect herbicide resistance?
Steven Gower,
MSU Diagnostic Services
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Several weed species have developed resistance
to popular herbicides used in Michigan. There are at least 12 weed
biotypes resistant to one or more herbicides in the state. These
herbicide-resistant weed species have been documented in field,
vegetable, and fruit crops, as well as tree plantations and nurseries
throughout Michigan.
Once growers identify and confirm an herbicide-resistant
weed, they can then implement appropriate management strategies
to prevent or limit weed seed spread. If you suspect resistance
in any weed species and would like to confirm this, seedheads can
be collected upon maturity and submitted to MSU
Diagnostic Services for an herbicide resistance screen.
The next several weeks prior to harvest are perfect
for collecting mature, viable weed seed. Select plants that were
definitely sprayed (not along field edges or sprayer skips). Harvest
seedheads by cutting the stem just below the seedhead. Place seedheads
into a brown paper bag or collect seed in a small envelope or container.
Never seal plants or seed in plastic!
Fees associated with herbicide-resistant weed testing
are generally $30 per sample (a sample could include multiple plants
of the same species from one field). Two exceptions to this fee
are marestail (Conyza canadensis) and common lambsquarters
(Chenopodium album) from
Michigan soybean fields. These two weeds will be screened for resistance
and costs will be covered by checkoff dollars through the Michigan
Soybean Promotion Committee.
Please contact Steven Gower (517-432-9693, sgower@msu.edu) with any questions regarding sample collection.
Send samples to: Diagnostic Services, 101 Center for Integrated
Plant Systems, East Lansing, MI 48824-1311, Attn: Steven Gower.
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White mold in soybeans and dry beans
Pat Hart
Plant Pathology
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White mold, caused by the fungus Sclerotinia
sclerotiorium, occurs in years of excessive moisture. As a general
rule, an average of three inches of rain over any two-week period
provides sufficient moisture for sclerotia to germinate and produce
ascospores. This translates into continuously wet soils for ten
days. Early row closure to maintain a wet soil surface is important.
The last week of June is the time to start adding up the rainfall
totals, and continue through July 15-20. It would appear that some
areas of the state may have received sufficient rain since the last
week of June to keep the soils wet enough. Continued wet weather
should favor germination of the sclerotia. Sclerotia are the black,
hardened structures that allow the fungus to survive for many years
in the soil, and the ascospores are responsible for infecting the
plants during times of susceptibility. Ascospores only infect flowers,
so the production and release of ascospores is important only during
flowering.
In both soybeans and dry beans, the earlier stages
of flowering are more important than later stages. Therefore, chemical
controls are only economically effective when applied at the earlier
stages of flowering. In dry beans, the best results have been obtained
when Topsin M is applied prior to 100% bloom (100% of the plants
have at least one open flower) at the rate of 1.5 lbs per acre.
Significant losses in yield occur only when a substantial number
of plants are infected, generally between 25% and 35% infection
will be required before losses are observed. This is true for both
soybeans and dry beans. This will depend somewhat on the pattern
of plant infection, but healthy soybeans and dry bean plants will
compensate for yield losses in infected plants. Fields with a history
of white mold are the most likely candidates for an economic return
from chemical control applications.
Fungicides have been less effective at controlling
white mold in soybeans and are not recommended. Some control has
been achieved when the herbicide Cobra was applied at the R1 growth
stage. However, timing is critical and if white mold does not develop
a yield reduction due to the Cobra will occur. Cobra has not been
effective every year or in every trial. Under low disease pressure,
yield protection may not
occur. Cobra was most effective when used in conjunction with soybean
varieties highly susceptible to white mold. MSU field trials used
6 oz of Cobra and 1 pint of crop oil/acre. The University of Wisconsin
has shown similar results using 2-4 oz of Cobra/acre.
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Ergot of rye and other small grains
in 2004
Pat Hart
Plant Pathology
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Ergot, caused by the fungus Claviceps purpurea,
is a disease of cereal crops and grasses. The disease causes reduced
yield and quality of grains and hay and also causes a livestock
disease called ergotism, if infected grains or hay are fed. The
disease cycle of the ergot fungus was first described in the 1800s,
but the connection with ergot and epidemics among people and animals
was known several hundred years earlier. Ergot's medicinal applications
and animal poisoning properties first called attention to this plant
disease. Human poisoning was common in Europe in the Middle Ages
when ergoty rye bread was often consumed.
Ergot occurs to some extent every year on cereals
and grasses in Michigan. The disease is generally more prevalent
in rye and triticale than in other cereals. Although the crop loss
caused by this disease is important, the effects of the ergot's
alkaloid toxins on man and animals is of much greater significance.
There has been an unconfirmed report of ergot in rye in Michigan
in 2004.
Ergot may affect the market grade of grain. In
the commercial grain trade, wheat is graded as "ergoty"
when it contains more than 0.05 percent by weight of the ergot sclerotia;
rye is graded as "ergoty" when it contains more than 0.3
percent by weight of ergot sclerotia, and triticale, oat, or barley
are "ergoty" when they contain more than 0.1 percent.
Additional information of ergot of rye can be found
at the following web sites:
http://www.botany.hawaii.edu/faculty/wong/BOT135/LECT12.HTM
http://www.ext.nodak.edu/extpubs/plantsci/crops/pp551w.htm
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Late blight in potatoes
Willy Kirk
Plant Pathology
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Late blight has been confirmed in many fields in
several counties in the Lower Peninsula. Recommendations for control
measures can be found at: http://www.lateblight.org
or in the May
19, 2004 Vegetable CAT Alert.
It is vital that loci (areas with plants with greater
than 20 percent foliar or stem lesions) are chemically destroyed
with gramoxone (rate = 1.5 pt/A) 30 rows either side of the last
visible lesion and 100 feet along the rows. Lesions do not become
visible until seven days after infection. Given the near perfect
conditions for late blight development this season, which include
recurring and continuous rain days, as well as steady and sometimes-strong
winds, the spores of this disease are plentiful and are carried
both within crops and between crops.
Fungicide programs must include a translaminar
late blight product at this stage and continue until the epidemic
abates; these include Previcur Flex, Tanos, Curzate, Acrobat, and
Gavel. These fungicides are best mixed with a residual laminar protectant
such as a chlorothalonil-based or EBDC-based product or Omega at
full label rate. Antisporulant products such as Supertin, Agritin,
or the copper products Champ and Kocide should also be considered
in the mixture, especially where late blight is present in the field.
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Late Blight Open House Day at Muck
Farm
Willy Kirk
Plant Pathology
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Given the dramatic re-appearance
of late blight in Michigan, it has been requested by many in the potato
industry that the late blight open day at the Muck Farm should be
held this year. Arrangements still need to be finalized, but the tentative
date is August 26 (Thursday) from 10:00 AM to 12:00 PM followed by
a lunch sponsored by the Michigan Potato Industry Commission. |
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1
- Southeast
Mike Score
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Commodity reports
Corn is well past pollination across the southeast
region. Early kernel counts are encouraging in fields that developed
well through wet weather. Nitrogen and potassium deficiency symptoms
are common, despite fertilizer application rates based on soil test
results. Even fields where PSNTs were used to assess need of nitrogen
application show yellowing along leaf mid-ribs.
Damaging insects in soybeans have been held
in check by consistent, sometimes heavy rainfall. We do have fields
where white mold has developed. This was expected, given wet weather
patterns that have passed through our region. Some farmers report
applying fungicides to control other diseases in soybeans, however,
most farmers are on cruise control between now and harvest. After
this week even intervention to control rising insect populations
would be questionable.
Wheat harvest ended a couple of weeks back.
Yields in our region were down 20 to 30% from normal. Test weights
were adversely affected by weather, with test weights of 49 to 56
commonly reported.
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3
- West Central
Fred Springborn
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Weather
High temperatures
were above 80 degrees 5 out of the last 21 days and below 70, 3
out of the last 21. Low temperatures have been in the upper 40's
to lower 60's. Rainfall totals have been variable. Some areas of
the region have received enough rainfall to maintain adiquate soil
moisture while others have received only a few hundreths of an inch
at a time and have very dry surface soils.
Commodity reports
The third cutting
harvest of alfalfa is progressing and complete on many farms.
Fields need to be monitored for potato leafhopper, though numbers
are declining in many areas. Harvesting dry hay continues to be
very difficult everywhere.
Wheat harvest is generally complete. Yields were 10 to
20% below average. Vomitoxin levels were variable and generally
above 3ppm. Oats and barley are being harvested and
yields are generally good.
The corn condition overall is
fair to good but growth is behind normal. We will need some good
summer time weather to make this crop.
Soybeans, like corn, are variable in condition
and growth stage. Soybean aphid numbers remain low. Dry beans
are growing well overall but are behind normal in development.
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5
- Thumb
Mark Seamon
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Weather
The word variable describes the weather here. Spotty
rainfall has occurred in some places but most growers in the area
are becoming concerned with soil moisture due to the high use of
water by the crop and limited rainfall. Cool temperatures (highs
in the 60's) are concerning growers with late planted crops.
The potato leafhoppers continue to feed on many
alfalfa fields. Much of this crop continues to grow well.
The sugar beet crop is looking better than
most crops in this area. Cercospera leafspot has been found in most
fields but has been slow in development this year. Refer to the
website for detailed local data at: www.MichiganBeets.com.
This site will help you in decision making with
fungicide application timing. Light colored leaves are showing up
in some areas. This seems most prevalent where the soil was saturated
for an extended period and may have caused denitrification.
Most early planted corn is looking and has
had good weather conditions during pollination. Late planted corn
is pollinating at this time, also with good conditions. The taller
corn now has blocked the view of problem areas in many fields so
we don't have to look at it.
Wheat harvest has wrapped up in this area
with less than record-breaking yields but not a bad crop. Vomitoxin
levels were variable with the highest levels in southern Saginaw
County and lower levels in the eastern and northern Thumb. This
appears to be related to the date of flowering of the wheat. MSU
wheat variety trial results can be found on-line at: web1.msue.msu.edu/msuwheat/Variety_Results.html
for those making planting decisions for this fall.
Growth has been slow but soybeans are looking
better with each week. Soybean cyst nematode symptoms are appearing
in some areas. Pod development on early planted soybeans looks good.
Many dry bean fields are looking good now.
Some root diseases may cause some loss of yield but many fields
have outgrown above ground plant symptoms.
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6
- Northern Lower Peninsula
Dave Glenn
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Weather
Cool weather the past week has slowed growth way down
again. Lows in the upper 40's and highs in the 60's. Rain showers
have occurred almost daily the past three days. Rain totals of 1
to 2 inches are common. Warmer weather this weekend should get things
back on track.
Commodity reports
Corn is all tasseled
now and looking pretty good. A late fall will be necessary to finish
most fields.
Wheat harvest
started last week with yields running from 40-70 bu/acre. Test weights
are running very good ranging from 57-61. Scab is spotty and not
too bad.
Soybeans are
starting to pod up nicely, but are fairly short yet. Again, a late
fall will be necessary. Aphids have been found but in extremely
low densities.
Dry beans are
filling in the rows nicely with pod set and filling occurring now.
Second cutting of alfalfa
is completed now with yields hitting on the high side of average.
Quality has been good with great weather and rainfall this year.
Oats and rye
are almost ready for harvest. Potatoes are bulking nicely
with no major diseases noted to date.
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Weather
news
Jeff Andresen
and Tracy Aichele
Agricultural Meteorology
Geography
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A fall-like upper air troughing pattern will persist
over the Great Lakes region and much of the northeastern US for
the next several days, which will lead to the continuation of an
unseasonably cool weather pattern across the state into the upcoming
weekend. Given unusually cold air in the trough above the surface,
scattered showers and isolated thundershowers are possible Thursday
and Friday, with less likelihood in the Upper Peninsula. Drier weather
is expected by late Friday and should continue into the weekend.
Temperatures during the next few days will remain well below normal
with highs ranging from the low 60's north to the low or mid 70's
south and lows remaining in the upper 40's and low 50's. A warming
trend is expected to bring temperatures back to normal levels for
Monday through Wednesday. The next chance for significant rainfall
will be early next week, most likely in the Monday or Tuesday time
frame.
The upper air troughing pattern mentioned above
has persisted off and on for much of the current growing season
since late May. It is meteorologically very unusual to see a pattern
continue this long, even in a stable season (summer, winter). That
being said, latest forecast guidance in the medium range time frame
suggests an overall continuation of the upper air troughing pattern
with northwesterly flow expected across the Great Lakes region during
the next one to two weeks. Not surprisingly, the NOAA 6-10 day
outlook, covering August 17-21 calls for below normal temperatures
and above normal precipitation across Michigan. The 8-14 day outlook
for August 19-25 calls for normal temperatures across the state,
with above normal precipitation expected in the southern half of
the Lower Peninsula and normal precipitation expected in the rest
of the state.
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