Welcome!
April
12, 2016
CHECK ALFALFA STANDS
Although the winter
was relatively mild, we are finding some areas of winterkill in Delaware and Dubuque
Counties. I spent several hours surveying hay fields in Jackson and northern Clinton
Counties and found no evidence of winterkill in those counties, but it is always the
better part of valor to check all fields.
Brian Lang, my
counterpart to the north, wrote the following:
ALFALFA
Winter Injury
We are finding
winterkill of alfalfa (and orchardgrass) in fields that were
cut late fall at the usual 2-inch cutting height such that no significant stubble height
was left entering winter. Alfalfa best management practices suggest that you leave
more than 6 inches of stubble in the field with these late harvests. This
recommendation has been in place for decades. Granted, there are times where this
recommendations doesnt seem to matter much, but other times it does. This
winter appears to be one of those times.
Every field that I
have seen where a good amount of stubble was left going into the winter, appears to be
just fine. However, I
cant make a blanket statement that all fields with good stubble are good, and all
late fall harvested fields left without stubble are bad. Each field has to be
evaluated. There are too many other management factors that can add to or protect
from stresses contributing to winter injury:
(1) proper soil pH and
fertility levels
(2) variety winter
hardiness
(3) disease resistance
package
(4) soil drainage
(5) age of stand
(6) intensity and
timeliness of cutting schedule
(7) timely pest control (i.e.
Potato leafhopper)
(8) wheel traffic; and
(9) leaving
more than 6 inches stubble in fall.
Factors we have no
control over include temperature and moisture. Regarding temperature, it was a mild
winter. Regarding moisture, alfalfa does not harden-up into winter near as well with a wet
fall compared to a dry fall. This last factor put overwintering alfalfa at some
risk. Adding too much stress from one or more of the other factors listed above
could cause winter injury at varying degrees and areas in fields.
I attached
a document with photos and comments on a couple of fields that I scouted (Friday,
April 8, 2016) in the New Vienna area. It is obvious that both fields need to be
rotated.
Its easier to assess plant symmetry during early growth,
and if the stand is poor, a more timely decision can be made for establishing a
replacement stand.
Observation |
Condition |
Action |
At green-up |
||
Large dead areas |
Plan to rotate. |
|
Small dead areas |
Some stand loss |
Consider
reseeding small areas. |
Random injury of
a few plants or very small areas |
Some stand loss |
Consider stand as a
whole
|
General plant
health appears normal |
Little to no
damage observed |
Recheck in 2
weeks to be sure |
Recommended plant
counts per square foot |
||
Full alfalfa
stand |
Alfalfa-grass mix |
|
Seeding year |
>20 plants in
fall |
>12 plants in
fall |
1st
production year |
>12 plants in
spring |
>8 plants in
spring |
2nd
production year |
>8 plants in
spring |
>6 plants in
spring |
3rd
production year |
>5 plants in
spring |
>4 plants in
spring |
At 3-inch growth |
||
Damaged areas
larger; plant health deteriorating |
Stand is getting
worse |
Is stand adequate?
|
General plant
health normal or improving |
Little or no
damage |
Plan for normal
harvest. |
At 6-inch
regrowth |
||
Plant growth is
far enough along for the stem-count evaluation method. |
>55 stems per
sq. ft. |
Plan for 100%
normal season yield. |
55-40 stems per
sq. ft. |
Expect 0 to 30%
season yield reduction. |
|
<40 stems per
sq. ft. |
Consider rotating
unless grass mix is present; if so, fertilize with N to encourage the grass. |
A nice reference to
have for alfalfa stand evaluations: http://learningstore.uwex.edu/assets/pdfs/A3620.pdf.
In addition, Dr.
Steve Barnhart, ISU Extension Forage Specialist Emeritus, posted basic information on
stand evaluation of alfalfa and other forages at: https://www.extension.iastate.edu/CropNews/2010/0318barnhart.htm;
the article is six years old but is still appropriate. It also includes links to other
forage references.
SEEDING FORAGES AND
WATERWAYS
In general, try to
complete seeding of cool season forage grasses and legumes before May 1 as seeding after
May 1 increases the likelihood that seeds will germinate but less frequent rainfall will
allow the soil to dry out before roots are deep enough to reach moist soil, killing the
seedlings.
YIELD POTENTIAL FOR
SMALL GRAINS DECLINES AFTER ABOUT APRIL 15
For those who may
not have their spring seeding of small grains done yet, potential yields decline for both
oats and wheat about 10% per week for each week planting is delayed after April 15, and an
additional 15% per week if planting is delayed beyond May 1. See Chapter 4 of the Illinois
Agronomy Handbook, beginning on the page numbered 43 (spring wheat) and 44 (oats), for
more details.
COVER CROPS
Rye cover crops
that will not be utilized as forage should be killed soon (if not already killed) if the
field will be planted to corn; in general a height of 6 inches is probably the best.
Waiting until it gets taller can be problematic for a couple of reasons:
1)
the more growth,
the harder the rye is to kill, and
2)
the more growth, the
more likely it will interfere with the following corn crop yield.
Additionally,
because of the corn yield suppression concerns, it is usually recommended to not plant the
field to corn for about 2 weeks after the rye has been terminated; the later the rye is
terminated, the later the corn will be planted.
Some herbicides may
reduce glyphosate efficacy when mixed with glyphosate; see "Terminating Cover Crops"
by Bob Hartzler, Extension Weeds Specialist. In this article, Hartzler also notes that
night temperatures of less than 40 degrees may reduce glyphosate activity.
WEEDS
No-till Fields
Winter annual
weeds, perennials, and some summer annual weeds are present in some no-till fields. As we
progress through the spring, remember that larger broadleaf weeds may take more than a the
pint/A rate of 2,4-D. Corn can be planted 7 days after a pint
or less of 2,4-D but 14 days after more than a pint of 2,4-D, and soybeans can be planted
15 days after a pint or less of 2,4-D but 30 days after more than a pint of 2,4-D.
It should also be
remembered that cool temperatures can diminish the activity of burndown herbicides; See Hartzlers article at http://crops.extension.iastate.edu/cropnews/2016/04/cold-temperatures-and-burndown-herbicides.
Glyphosate Resistant
Waterhemp
We continue
witnessing more and more fields with waterhemp that does not respond to glyphosate. When
finalizing herbicide decisions, be sure diverse waterhemp strategies are part of the plan.
Use multiple effective Herbicide Groups and be sure
the active ingredients are applied at effective rates; the full rate of many pre-mixes do
not apply the same amount of active ingredient as is applied if the
single-active-ingredient product is applied. To compare products,
Liquid products:
1.
Calculate the
fraction of a gallon to be applied per acre (quarts divided by 4, pints divided by 8,
fluid ounces divided by 128)
2.
Multiply the above
by the pounds of active ingredient per gallon, as shown in the active ingredients section
at the beginning of the label.
Example: If 3.0 fl.
oz. are going to be applied per acre, and the label indicates it has 4.0 pounds of active
ingredient per gallon, then 3 / 128 X 4 = 0.09375 pounds of active ingredient per acre.
Dry products:
1.
Calculate the
(fraction of a) pound(s) to be applied per acre (ounces divided by 16)
2.
Multiply the above
by the per cent of active ingredient, as shown in the active ingredients section of the
label.
Example: If 2.2
pounds are going to be applied per acre, and the label indicates it is 90% active
ingredient, then 2.2 X 0.90= 1.98 pounds of active ingredient per acre.
In general, if a pre-mix
applies 70% of more of the amount of the active ingredient found in effective
single-active-ingredient products, it is probably O.K. If the rate is less than 70%,
consider a strategy to fill the gap.
Some soil applied
products that are effective on waterhemp are shown in the table below.
Herbicide
Group |
Type |
Corn |
Soybean |
3 |
DNA |
Prowl, Treflan |
|
5 |
Triazine |
Atrazine |
Metribuzin
(Sencor) |
14 |
PPO Inhibitor |
Kixor
product (Sharpen, etc.) |
Authority, Valor |
15 |
amide |
Dual, Harness,
Outlook, Warrant, Zidua, etc. |
Dual, Intrro, Outlook, Warrant, Zidua, etc. |
27 |
HPPD Inhibitor |
Balance, Callisto, etc. |
Some post-emergent
herbicides that are effective on waterhemp are shown in the table below.
Herbicide
Group |
Type |
Corn |
Soybean |
4 |
Plant Growth
Regulator |
2,4-D, Banvel, Clarity, Status, Yukon, etc. |
|
5 |
triazine |
atrazine |
|
14 |
PPO Inhibitor |
Blazer,
Cobra/Phoenix, Flexstar/Reflex/Rumble |
|
27 |
HPPD Inhibitor |
Callisto,
Impact, Laudis, etc. |
Many pre-emergent
herbicides are now also labelled to be applied post-emergence, which allows the product to
be applied later in the season to extend residual activity. In this instance, Bob
Hartzler, suggests splitting the herbicide application, which is sometimes called
"layer residuals." See "Two Apps Are Better Than One. "
And although it is
not possible on all fields nor is it popular, rotary hoeing and cultivating are still very
effective.
CORN
Nitrogen
For those who
applied anhydrous ammonia last fall, many are wondering about how much was lost with the
unusually wet weather last December. John Sawyer, Extension Soil Fertility Specialist,
wrote about that at http://crops.extension.iastate.edu/cropnews/2015/12/nitrogen-loss.
For those that did
not apply anhydrous ammonia last fall, corn prices have fallen more rapidly that nitrogen
prices, resulting in many people re-assessing their nitrogen fertilizer practices. Sawyer
wrote an article in late 2014 that is still timely today; it can be found at http://www.agronext.iastate.edu/soilfertility/currenttopics/NitrogenFertilizationRates_10-14-2014.pdf.
It refers to the Corn Nitrogen Rate Calculator, which is at http://extension.agron.iastate.edu/soilfertility/nrate.aspx.
Note that in soils
classified as having natural drainage classified as poorly drained or very poorly drained,
higher nitrogen rates are now suggested; see https://store.extension.iastate.edu/Product/Nitrogen-Use-in-Iowa-Corn-Production,
page 4.
If you are
concerned about having enough nitrogen in the event of wet weather, recent analysis done
by Sawyer suggests that a good approach is to use the recommended rate of nitrogen
fertilizer and then monitor spring rainfall. In Southeast Iowa, add the total rainfall for
March, April, May, and June; if it is over 17 inches, apply supplemental nitrogen
fertilizer. Elsewhere, if the total rainfall for April, May, and June is over 16 inches,
apply supplemental nitrogen fertilizer. If supplemental nitrogen fertilizer is needed, 50
units is a good number. More information on this concept is at http://crops.extension.iastate.edu/cropnews/2015/06/nitrogen-issues-so-far-spring.
Planting
Be
sure to take time before and during planting to adjust, monitor, and re-adjust your
planter as soil conditions vary. Mark Hanna, Extension Agricultural and Biosystems
Engineer, wrote a good article at: http://crops.extension.iastate.edu/cropnews/2010/04/remember-check-planter-settings;
it has some age on it, but the principles still apply. Planting errors haunt all season,
so taking time to closely monitor and adjust is time well spent.
In general, farmers
have been patiently waiting for soils to warm up before planting corn. It is important to
wait until the soil temperatures are near 50 degrees and warming before starting to plant.
See "Corn
planting: Consider soil temperature and date" by Roger Elmore and Lori Abendroth.
Soil temperatures can be found at http://mesonet.agron.iastate.edu/data/soilt_day1.png.
We still have 20 days or more left in the ideal planting time; see "Updated
planting date recommendations for Iowa" by Roger Elmore and Lori Abendroth.
CALENDAR ITEMS
Spring Field Day -
Muscatine Island Research and Demonstration Farm
5:30 p.m., Tuesday,
June 21, 2016
Fruitland
Details will appear
at: https://www.extension.iastate.edu/Pages/eccrops/meetmusc.html.
Hay & Forage
Expo
June 22 - 23, 2016
Boone, IA
See: http://hayexpo.com/
Spring Field Day -
Southeast Research and Demonstration Farm
1:00 p.m., Thursday,
June 23, 2016
Crawfordsville, IA
In addition,
training for Certified Crop Advisors will be conducted, beginning at 9:00 a.m.
Details will appear
at: https://www.extension.iastate.edu/Pages/eccrops/meetserc.html.
Spring Field Day -
Northeast Research and Demonstration Farm
1:00 p.m., Tuesday,
June 28, 2016
Nashua, IA
Details will appear
at: https://www.extension.iastate.edu/Pages/eccrops/meetnerf.html.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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