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 doesn’t 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 can’t 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.  …  It’s 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 if it’s too thin to keep – rotate if unsure – recheck in 2 weeks
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? No, rotate. Yes/maybe, recheck in 2 weeks.
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 Hartzler’s 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.