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ISSUE 6  JUNE 10, 1999

 

TRANSGENIC CANOLA REMINDERS

    There were some canola planted early and these fields could need an application of a
herbicide for wildoats soon. Wild oats can be a weakness with Liberty Link and IMI canola.
These herbicides are effective on wild oats, however percent control drops quickly once the
wild oat reaches the fourth leaf stage.

 

LIBERTY REMINDERS:

- Effective on annual broadleaves, less effective on large grassy weeds (wild oat).
- Suppression only of perennial weeds.
- Weak on larger grasses ( 4 leaf +), can add 5 oz Assure II or 6 oz of Poast/acre.
- Might need to consider spot spraying wild oats before spraying the entire field.
- Optimum spraying timing is sunny, warm conditions.
- Spray a minimum of 2 hours before sunset.
- Add 3 pounds of ammonium sulfate per acre.

 

ROUNDUP REMINDERS:

- Effective on annual broadleaf and grassy weeds.
- Maximum application rate 1 pint per acre.
- Allowed two split applications of 1 pint/acre per season.
- Applications can be made from emergence prior to bolting.
- Two applications will be needed for perennial weeds (Canada thistle), kochia, and
    wild buckwheat.

 

RAPTOR (IMI CANOLA) REMINDERS:

- Control of many annual broadleaf and grassy weeds.
- Same family as the ALS herbicides and will not control kochia resistant to ALS
    herbicides (Ally, Express, etc).
- Application rate is 4 oz/acre.
- Timing important, especially for grasses. Spraying early will insure small (1-4 leaf) wild
    oat and yellow foxtail. Might need to consider spot spraying wild oats before spraying
    the entire field.
- Will give some residual control on mustard species and foxtails

Kent McKay
Area Extension Agronomist
North Central Research and Extension Center
kmckay@ndsuext.nodak.edu

 

SECTION 18 AMENDMENT FOR RAPTOR ON DRY BEANS

    North Dakota has received EPA approval to amend the Section 18 for Raptor to
allow aerial application on dry beans. Aerial application equipment must be properly
calibrated and product must be applied in 5 or more gallons of water per acre. All
other conditions from the original authorization still apply.

 

TIMING OF POSTEMERGENCE CORN AND SOYBEAN WEED CONTROL

    The growth of weeds, as is the case for most biological organisms (e.g., teenagers),
is logarithmic. Growth starts slowly but soon occurs rapidly. Effectiveness and crop
injury problems can be attributed to herbicide application to weeds and crops that are
too large. Most postemergence herbicide labels list the ranges of weed and crop heights
over which herbicide effectiveness will be maximized and crop injury will be minimized.
With the advent of herbicide- resistant crops, the concern over herbicide-induced injury
to larger crop growth stages has been reduced but not eliminated if you are tank mixing
with other herbicide modes of action (e.g. plant growth regulators).

    However, the need for a timely herbicide application to maximize effectiveness and
to minimize weed-crop interference is important. For example, in the Roundup Ready
corn system, the glyphosate label states that theherbicide should first be applied when
weeds are 4 inches in height. In the Roundup Ready soybean system, the glyphosate
label states that weeds should be controlled in the 4- to 8-inch height range. Experience
has taught us that translating weed height into units of time (i.e., days after crop planting)
helps growers integrate weed and crop biology restrictions into their time and labor
framework. Under most spring and early summer cropping conditions it takes approximately
four weeks for foxtail to reach 4 inches in height and approximately six weeks for the foxtail
to reach 8 inches in height.

    Therefore, based on the glyphosate label, a crop producer has about a two-week interval
to complete a glyphosate weed management program in soybean, and a glyphosate weed
management program in corn should be initiated approximately one month after corn planting
when foxtails are 4 inches tall. Disruption of the time of application framework could mean
poor weed control or yield loss due to weed-crop competition.

    Based on current cropping conditions, it is important to be ready to apply postemergence
grass herbicides in corn as soon as the grass weeds approach 3 to 4 inches in height. For fields
where the corn is still under 5 to 11 inches in height, some of the preemergence herbicides can
still provide some residual weed control and reduce the need to treat all fields in such a
timely postemergence manner.

Roundup Ready soybeans in North Dakota are generally in their first year of production. This
is still a new weed control concept for many growers so producers are asking questions and
experimenting with rates and timing of the application. Here are things producers need to
remember when making roundup ready decisions this growing season.

-Roundup Ultra and Roundup Original are the only formulations of Glyphosate labeled for use
on Roundup Ready Soybeans.

-Remember that annual grass weeds are easier to control with Roundup than are annual
broadleaf weeds, and annual broadleaf weeds are easier control to control than perennial
weeds. Annual weeds are controlled easiest with Roundup when they are young.

-Perennial weeds should be sprayed when they are in the bud to early flower stage for best
long-term control.

-Soybeans tolerate early weed pressure better than corn. If wet weather delays herbicide
spraying, corn fields should be sprayed (with any post-emerge herbicide) before soybean
fields if weeds are at the same stage of growth.

-RATES: Monsanto is offering their technology value package, which it appears many
growers will adopt. In conventional tillage, growers who use 32 ounces per acre on 4-8 inch
weeds are eligible for 12 ounces of Roundup Ultra free if a minimum of 24 ounces is re-sprayed.

    If the crop is under moisture stress, plan the first application for weeds in the 4-6
inch stage. On the other hand, the application can be delayed to the 6-8 inch stage if soil
moisture is good. When the most difficult annual broadleaf weeds-waterhemp, velvetleaf,
Pennsylvania smartweed, and black nightshade-exceed 6 inches in height, growers should
increase rates of Roundup Ultra from 24 ounces to 32 ounces and increase the rate to 48
ounces when these weeds exceed 12 inches. Ridge till farmers who apply very low rates
preplant or at the cracking stage may experience better weed control by avoiding early
morning and evening sprayings.

-Weeds such as waterhemp and black nightshade germinate late in spring so a delayed
or second application is necessary if these types of weeds have a field history.

-Ammonium sulfate (AMS) is an insurance policy for optimum weed control. Studies
show AMS improves weed control of tough-to-control weeds under adverse weather
conditions-either droughty or cold temperatures (less than 55 degrees F). AMS also
appears to improve weed control when spraying with hard water testing more than 500 ppm.
When mixing the spray solution, ammonium sulfate should be added before Roundup Ultra
to the tank.

-Annual weeds are normally more competitive with the cropthan perennial weeds. In a
Roundup Ready management plan, annual weeds should be the first priority in the timing
of the application.

-One application of Roundup Ultra should be enough if growers are solid seeding soybeans.

-Last but not least, make sure fields to be sprayed with Roundup are Roundup Ready
soybean varieties.

- Adapted from MN Crop Newsletter, by Dr Jeff Gunsolus, U of MN Extension Weed Scientist.

Richard Zollinger
NDSU Extension Weed Specialist
rzolling@ndsuext.nodak.edu

 

HYBRIDS DIFFER FROM HERBICIDE AFFECTS

    Labeled corn herbicides are suppose to be safe to use on corn. However, questions
frequently come up on hybrid sensitivity to specific herbicides. Many of the major seed
companies screen their inbreds and breeding lines, discarding sensitive lines. Golden Harvest
started a program in the mid-1980s to test for visual differences in hybrid response to
herbicides and other companies jumped on the bandwagon.

    Pioneer currently has a program in place to test hybrids. Within their program, Pioneer
ranks hybrids to each individual herbicide as: adequate tolerance; requires careful
management; not recommended; or, insufficient data

http://www.pioneer.com/usa/crop_management/national/corn_herbicide_guide_1999.htm

    This information is often pulled from label specifications or are results from trials. Other
companies also have collected information over the years on company sales and research plots
that may provide valuable information. Unfortunately, sharing the information can be a real
dilemma for seed companies.

    Indeed, experience has shown that certain herbicide and hybrid interactions do have the
potential to produce crop injury or reduce yields. On the other hand, occasionally some
yield enhancement with chemicals is seen whether from straight weed control or other
interactive factors that favorably influence plant growth for that season. With postemergence
chemicals, the interaction often depends on the herbicide mode of action.

    You are always more likely to see injury with stressful environmental conditions immediately
before or after an application. Indeed, environmental differences are the biggest factors in crop
injury. Injury can be expressed differently from year to year. Some years may show an early
season response, while other years may not show a herbicide impact until mid-season,
making the problem difficult to deduce. And, the problem may show up in a variety of forms.
Physical injury, reduced stands, slower growth, delayed silking and tasseling may be individual
results seen alone or in combinations.

    The best way to keep tabs on how well your herbicide and hybrid program is working is to
monitor crops and keep records on the dates and weather conditions at the time of spraying
and around that application timing.

 

THINK LONG-RANGE WEED SEED CONTROL

    In years of poor crop prices and dismal cropping conditions, some key inputs in farming are thrown
out the door such as better crop seed and weed control. However, these two inputs alone substantially
make or break a farm in the long run.

    Good, clean, high-germ crop seed is most important. Seed will determine your stand, plant vigor
and yield. Weed control done now affects the farm for years, sometimes decades.

    Some weed species produce an amazing number of viable seed. Minnesota studies done back
in the late 1940s did weed-seed counts on 24 different plots across four locations that found 98 to
3068 viable weed seed per square foot down six inches deep in the soil. On a per acre basis, this
weed seed bank is between 4.3 million to 133 million seeds in the upper plow layer.

    Weed escapes can add substantially to this weed bank. Kochia can produce an average of 14,600
seed per plant; wild oats, 250 seed per plant; redroot pigweed, 117,400 seed per plant; Canada thistle,
680 seed per plant; and, barnyardgrass, 7,160 seed per plant.

Denise A. McWilliams
Extension Crop Production Specialist
dmcwilli@ndsuext.nodak.edu

 


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