April 26, 2007

In this issue

§ Sandhill crane repellent (Avitec) available in 2007

§ Soil-applied residual herbicide benefits in soybeans

§ Soybean seeding rates

§ New crop and pest management soybean hotline

§ Soybean rust and freezing temperatures in the south

§ Soybean rust fungicide update for early 2007

§ Increased Michigan coverage for Fusarium head blight risk assessment tool

§ Management of foliar wheat diseases, Part 2

§ Fungicide efficacy for control of wheat diseases

§ Fertilizer placement

§ How much winter injury did alfalfa receive from recent low temperatures?

§ Regional reports

§ Weather news

Sandhill crane repellent (Avitec) available in 2007

Christina DiFonzo, Entomology

The crane repellent Avitec is available again this summer for corn in Michigan (as well as Wisconsin and Minnesota) through the Section 18 process. The Section 18 is specifically to reduce crane damage in newly planted corn seed.

The crane problem

Crane populations and crop damage have risen over the last several decades. Harassment methods are time consuming and often do not work, and simply drive birds to neighboring fields. Recognizing the problem, the International Crane Foundation in Baraboo, Wisconsin studied how to prevent damage. They found that seed treatments containing lindane reduced feeding on seedlings. However, lindane is an old, persistent organochlorine insecticide that is mostly eliminated from the seed treatment market. The ICF continued to look for an alternative, hitting upon 9,10 anthraquinone, a natural plant-produced compound with low toxicity, in tests with captive birds. Anthraquinone is currently used as a goose repellent for parks, golf courses, schools, and lawns.

For agricultural use, anthraquinone is manufactured and sold by Arkion Life Sciences as Avitec. It can be applied as a liquid seed treatment by a commercial seed-treater, or by the do-it-your-selfer in the dry form as a planter box treatment. It is NOT a restricted use pesticide, and you don’t need a DNR permit to apply it. However, you must have a copy of the Section 18 label at the time of application. Avitec repels cranes without harming them. The birds detect the treated seed and avoid feeding on the corn. However, cranes may still be present in treated fields, feeding on other seeds, worms or insects.

Important notes on Avitec use and price

In 2006, most of the Avitec used was in the powder form as a planter box treatment. The state with the highest number of acres treated last year was Wisconsin (est. 40,000 acres). Dr. Eileen Cullen, the field crops entomologist at the University of Wisconsin, reports “relatively few complaint calls, as well as positive feedback from growers. The powder worked well…. There were reports of inconsistency in some cases in terms of the amount of powder retained on the seed. The dose per seed varied with some planter types, and in cases where growers added graphite or talc to the hopper box or filled the box too full, did not thoroughly mix, etc. In all reported cases, Arkion worked with the growers and solved the issues for the most part.”

Note that the product label for the dry formulation of Avitec indicates that the powder must be mixed thoroughly into the planter box. Also, graphite and talc should NOT be added when using the dry Avitec formulation. If you have time to get seed treated with the liquid product, that should solve some of these problems and improve consistency. However, used properly, the dry formulation appears to work well.

The target cost for Avitec is about $5 per acre. That price may vary a bit depending on the local distributor. If you have trouble finding Avitec in your area, or are quoted a price considerably above $5, Arkion urges you to call them directly or visit their web site (contact information at the end of this article). They can help you find a dealer and a reasonable price.

Crane biology related to crop damage

Cranes are amazing birds. They are considered the oldest living bird species, as close as we can get to dinosaurs. But they can also be destructive to crops. Sandhill cranes return to Michigan each spring to mate and lay eggs in wetland areas. Mating pairs and chicks (1 to 2) feed in wetlands and move into upland areas such as pastures and fields. Pairs are territorial; with the small field sizes in Michigan, there is usually only one pair plus offspring per field. Juvenile (year-old) cranes, however, have a different behavior. When they return to Michigan, they gather in large flocks that move from field to field. Jim Harding, a wildlife specialist with the MSU Museum, calls juvenile cranes “troublemakers” and he says “all there is for them to do is eat.” It is these large groups of hungry juveniles that cause the most crop damage. A nesting pair will drive groups of juveniles away, so it is technically an advantage to have a nesting pair in your field.

Sandhill cranes have a varied diet, eating plant tubers, seeds, insects, worms, mice, frogs, and snakes. Some of their feeding – on cutworms, grubs, and other soil pests – is beneficial to crop production. However, a crane can probe down into the ground with its long beak and pluck out germinating seed and seedlings as it walks down a row. A group of cranes can destroy acres of corn in a short period. The majority of crop damage from cranes is reported from southwestern Michigan (Hillsdale and Jackson Counties, west), an area with many small fields interspersed with lakes and wetlands.

Not many alternatives

Some growers have proposed feeding or baiting cranes by putting seed corn along field edges to lure them away from production fields. Every bird expert I talked to said NO to this idea. Cranes prefer the open middle of fields where they can see potential predators, so they probably wouldn’t stay on bait corn on a field edge. Also, in addition to grain, they eat high-protein food like insects, and thus naturally may wander from the baited area. Finally, baiting might make things worse by drawing additional birds to a field.

Harassment and removal (a nice way to say shooting) of birds is an option, but it is time consuming. A permit is required to kill cranes. To get information on obtaining a permit, call the USDA-APHIS Michigan Wildlife Service office in Okemos, Michigan, at (517) 336-1928. Note that a permit is less likely to be issued if you have not tried the Avitec repellent.

Important contact numbers

Avitec pricing, availability

Arkion Life Sciences LLC

Wilmington DE, 1-800-468-6324

http://www.arkionls.com/

Research on crane repellents, crane biology

International Crane Foundation (ICF)

Baraboo, WI 1-608-356-9462

http://www.savingcranes.org/conservation/our_projects/detail.cfm?did=4&cid=1&aid=43&pid=17

Section 18 labels for Avitec

Michigan Department of Agriculture

http://www.michigan.gov/mda/0,1607,7-125-1569_16988_35290-127656--,00.html

Permits for crane removal

USDA-APHIS Michigan Wildlife Services

2803 Jolly Road, Suite 100, Okemos, MI 48864

517-336-1928

Soil-applied residual herbicide benefits in soybeans

Christy Sprague
Crop & Soil Sciences

The use of postemergence (POST) glyphosate in Roundup Ready soybeans has been the primary weed control program used by many Michigan soybean growers. While this system has seemed to simplify weed management, relying on total postemergence herbicide programs can be difficult to manage if not properly implemented. The flexibility in application timing that glyphosate offers may make it easier to control larger weeds, however the benefits of early-season weed control to protect crop yield can be lost if applications are not made in a timely manner. Additionally, untimely applications can lead to a reduction in weed control. Another thing to consider is by relying only on glyphosate as the weed control strategy this system puts tremendous selection pressure on the weeds that could possibly lead to the development of herbicide-resistant weeds.

One way to help overcome some of these concerns is to implement the use of a soil-applied or preemergence (PRE) herbicide into your soybean weed control program. Using a planned PRE residual herbicide followed by a POST glyphosate application can result in more consistent weed control, reduces the size and number of weeds present at the POST application timing, and offers greater flexibility in the POST application window. One of the concerns that many producers have in implementing a PRE herbicide is the economics. While a PRE herbicide may increase the cost of your weed control program, resulting benefits often make up for the cost by increasing weed control and yield. Below are some of the benefits realized by PRE followed by POST weed control programs.

Reduced early-season weed competition

Using a PRE herbicide will control a number of weeds that would have emerged and competed with the crop as it becomes established. While early-season competition may not be a factor if the POST application is timed appropriately, (remember that weeds can increase in size in a number of days and if you are trying to spray a large number of acres or you become delayed in your applications due to rain) early-season weed competition can become a problem. Remember, for timely POST applications to avoid yield losses due to early-season weed competition MSU recommends weeds should be controlled before they are 4-inches in height in 7.5- and 15-inch rows and 6-inches in height in 30-inch rows.

Consistent control of weeds that continually emerge

Several weed species have continual emergence or emerge only later in the season. These species can include: annual grasses, giant ragweed (Southern Michigan), eastern black nightshade, pigweeds and common lambsquarters (occasionally). Because of the later emergence of these weeds, they may actually emerge after the POST herbicide application and can produce seed and become a problem at harvest. PRE herbicides allow for a delay in the POST applications, which will result in more effective control of these late-emerging weeds.

Consistent control of hard-to-control weeds

In Michigan, we have seen a few weeds that have become harder to control with one POST glyphosate application. Common lambsquarters and giant ragweed are examples of weeds that are not always effectively controlled with glyphosate. A PRE herbicide can aid in control by providing effective control or suppression of these weeds so they are easily controlled with the POST application. For example, over several MSU trials a PRE residual herbicide followed by POST glyphosate treatment has provided more consistent control of common lambsquarters than 1- or even 2-application of glyphosate (Figure 1).

Effective control of perennials

Control of perennial weeds is more effective in the later stages of growth (bud to flower stage). Because PRE residual herbicides will provide initial control of annual weeds the POST glyphosate application may correspond more appropriately to the stage of growth needed for perennial weed control.

Weed resistance management

One possible long-term benefit from including a PRE herbicide in your weed control program is the implementation of herbicide resistance management strategies. A PRE herbicide would include another mode of action into the weed management program and reduce the number of weeds present for the POST application. Ultimately, these two benefits will relieve the selection pressure of a glyphosate-only weed management system. This has become a much greater concern as we see more glyphosate-resistant weeds being reported around the United States.

Soybean seeding rates

Kurt Thelen
Crop & Soil Sciences

Recent research conducted in the North Central Corn Belt suggests that soybean planting populations may be able to be dialed back somewhat without compromising yield, or more importantly, profitability. Research conducted throughout the Midwest is showing that a final harvest population of 100,000 plants per acre is generally sufficient to achieve maximum yield. The challenge is in deciding what your seeding rate must be in order to achieve a final harvest population of 100,000 plants or higher.

What does this mean for Michigan soybean growers? With fall soybean price forecasts looking favorable, growers do not want to compromise yield. However, as mentioned above, recent Midwest studies clearly show that it is not necessary to continually increase soybean planting populations in order to obtain maximum yield. Unlike corn, soybean has a great propensity to compensate or “flex” when plant populations vary. Therefore, the optimal planting population range is wider for soybean than it is for corn. Determining the minimal scale of that optimal soybean planting population range will optimize profitability and still maintain yield. As a starting point, begin with a planting population of 175,000 seeds per acre for drilled systems and 130,000 seeds per acre for 30 inch rows and then adjust from there based upon field productivity and planting conditions. Low productivity fields require higher seeding rates to obtain maximum yield than do high productivity fields. Similarly, if forced to plant in less than optimal soil and planting conditions, adjust seeding rates upward to compensate for expected decreases in seedling emergence and survival.

Several things to consider when operating on the low end of the optimum planting population range include managing in a manner that maximizes emergence and seedling survival. Calibrate your drill or planter to ensure that seed drop is adequate and uniform across all rows. This is important to do every year as seed size and planter mechanical efficiency and wear can vary from year to year. Avoid planting when soil conditions are less than optimal to facilitate good seed to soil contact and seedling germination. Inoculate soybean seed with Rhizobium bacteria regardless of field history. Finally, if planting early in the season, consider using fungicide treated seed (be sure it is labeled for use with your soybean inoculant) to protect against soil borne root diseases.

New crop and pest management soybean hotline

Mike Staton
Van Buren County

Michigan soybean growers can access timely crop and pest management information through a new toll-free, soybean hotline. The toll-free number is (888) 201-9301. Growers will hear a recorded greeting directing them to select from six subject areas: insects, diseases, weeds, agronomic information, soybean cyst nematodes and the Michigan Automated Weather Network. Callers can listen to multiple topics without redialing the toll-free number. If you don’t get the information you need from the hotline, please call your local Michigan State University Extension office.

The updates and recommendations for each topic area will be recorded by Michigan State University Extension specialists. Messages will be updated as often as needed to provide Michigan soybean growers with the most up-to-date information for improving soybean yields and farm profitability. Topics will be added and updated under the main subject areas as needed from May through August.

The soybean hotline is a new and valuable resource for Michigan soybean producers. The hotline is sponsored by MSU Extension and The Michigan Soybean Checkoff and is part of the Soybean 2010 project.

Soybean rust and freezing temperatures in the south

Diane Brown-Rytlewski
Plant Pathology

You’ve probably read about the soybean rust found in early March on soybean residue from a bin of soybeans produced in Iowa in 2006, but if you haven’t you can read about it at the link listed here: http://www.plantpath.iastate.edu/soybeanrust/node/394 . Even though it’s early in the season, I thought that I’d start giving you some updates on what is happening with soybean rust so far this year further south.

On April 7-8, record low temperatures in the Florida Panhandle dipped below freezing for several hours. It is not known how this might impact the spread and build up of soybean rust on kudzu, but it will probably slow it down for a while. Before the frost, warm temperatures had increased the growth of kudzu throughout the Southeast. Scouting efforts are already underway on kudzu and emerging soybeans in southern sentinel plots. Soybean rust has been detected on kudzu in nine Florida counties and in five counties each in Georgia and Alabama. In some cases, the infected kudzu has been destroyed and rust in some of those locations is no longer found. Soybean rust was found on soybeans in one county in Texas, but that field has since been destroyed. Sentinel plot scouting will take place again this year in Michigan. We will provide more details to you as the season gets underway.

Editor’s note: see the national tracking web site for soybean rust at: http://www.sbrusa.net/

Soybean rust fungicide update for early 2007

Diane Brown-Rytlewski
Plant Pathology

Section 3 label for Domark fungicide on soybeans

Previously available only for soybean rust under a special Section 18 emergency use label, Domark (Valent USA Corporation) has received a new label (Section 3) allowing use on soybeans for soybean rust (as both a preventative and a curative), and a number of other soybean diseases.

New Section 18 label for Topguard

Topguard (Cheminova, Inc., flutriafol) is a triazole fungicide. Consult the accompanying table for a complete listing of fungicides currently registered for soybean rust in Michigan. There are other fungicides in the pipeline for Section 18 registrations for soybean rust. As they receive approval for use in Michigan, we’ll provide you with updates. (View label.)

Soybeans: Fungicides approved (Section 18) or registered (Section 3) for soybean rust management in Michigan – updated April 2007.

Active ingredient	Product (trade name)	Section 18 start date	Section 18 expiration	Section 3 Registration status
azoxystrobin	Quadris	none	none	Registered
azoxystrobin + propiconazole	Quilt	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07	See propiconazole.
chlorothalonil	Bravo, Echo, Equus	none	none	Registered
flutriafol	Topguard	New for 2007 covers use in 2007, 2008, and 2009 growing seasons-	Expires 2/12/10	Registration decision expected in 2009
myclobutanil	Laredo EC	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07	Tolerance approved; Registration decision expected in early 2007
propiconazole	Tilt	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07	Registered but final label is being reworded.
	PropiMax	covers use in 2005, 2006 and 2007 growing seasons
	Bumper	covers use in 2005, 2006 and 2007 growing seasons
propiconazole + trifloxystrobin	Stratego	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07	Registered but final label is being reworded.
pyraclostrobin	Headline	none	none	Registered
tebuconazole	Folicur	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07	Registration decision expected in mid 2007
	Orius	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07
tebuconazole + pyraclostrobin	Headline SBR	covers use in 2005, 2006 and 2007 growing seasons	expires 11/10/07	Not submitted for Section 3 registration
tetraconazole	Domark	covers use in 2005, 2006 and 2007 growing seasons; 2 applications/season requested	expires 11/10/07	Registered as of 4/4/07 Note: Rates have been decreased on the Section 3 label to 4-5 fl oz/A (from 4-6 fl oz/A) with a maximum of two applications.

Credit: Kent L. Smith, Plant Pathologist, UDSA, ARS, AO Office of Pest Management Policy; Marty Draper, National Program Leader,-Plant Pathology, CSREES; and Brian Hughes, Product Registration Manager, Mich. Dpt. of Ag.

Increased Michigan coverage for Fusarium head blight risk assessment tool

Diane Brown-Rytlewski
Plant Pathology

For the second year, I will be providing Michigan-specific commentary about weather conditions, wheat diseases and wheat developmental stages for the Penn State Fusarium head blight (FHB) model website. The Michigan Agricultural Weather Station Network (MAWN) weather station locations (48) have been added to the model website, providing significantly increased coverage for the state. The Penn State Model predicts the risk probability of epidemic conditions based on observed weather patterns. Separate models are used for spring and winter wheat. The winter wheat model is based on the interval of time that relative humidity is 90 percent or greater, with temperatures between 48 and 85°F (9 -30°C). Wheat is most susceptible to FHB infection during flowering. The model uses weather conditions observed during the seven days prior to the flowering date you select to predict the level of risk. You can select a risk prediction based on the previous seven days weather, six days and a 24-hour forecast, or five days and a 48-hour forecast.

The Penn State model is available at: http://www.wheatscab.psu.edu/. Select the risk map tool on the menu, then follow the directions to choose an assessment date, wheat type and state. Once you select the state (Michigan), the weather station locations will appear on a map of the state. Clicking on an individual station (represented by a purple circle or a red triangle) will bring up the previous seven days temperature, rainfall and risk probability for that station point. The models are tuned to reflect average rainfall. In the past, model predictions have not always reflected risk accurately when an area has been under extended periods of drought or higher-than-normal rainfall. A means to help address that issue has been to allow for input by the state extension specialist to provide additional commentary that may not be reflected by the risk maps, including information about rainfall or drought conditions and wheat growth stages in specific areas of the state.

The models have an accuracy of about 80 percent given the data used to develop and test the models. They are intended as a decision aid to be used along with other resources, such as weather forecasts, grain markets and local expert advice to help you with disease management decisions. Weather conditions that take place during flowering and grain fill of the crop are not part of the model, and could significantly affect the development of disease and accumulation of mycotoxins. This year, state-specific commentary will be available for all 24 states included in the model.

Management of foliar wheat diseases, Part 2

Diane Brown-Rytlewski and Willie Kirk, Plant Pathology
Martin Nagelkirk, MSUE Sanilac County

Recent freezing temperatures in Michigan caused some injury to wheat foliage. Injury is showing up as tip burn, and in low areas of fields as more extensive browning of leaves. The wheat should recover with little impact on yield. However, be watchful for diseases this spring, as the stress caused by freeze injury may cause wheat to be somewhat more susceptible to foliar diseases. Part two of this series covers leaf rust, stripe rust, and fungicides for managing foliar disease of wheat. As of mid April 2007, leaf rust has been showing up in parts of Texas and southern Kansas. A fact sheet containing the foliar disease management information from part one and part two can be found at: http://fieldcrop.msu.edu/documents/wheat%20foliar20%disease-final.pdf

Leaf rust

Cause: Wheat leaf rust, Puccinia triticina (fungus). (view image)

Symptoms: Infections first appear on the lower leaves. Reddish-orange spore masses of the fungus break through the leaf surface leaving an orange powder that rubs off the leaf. As the crop develops and matures, leaf rust generally appears on upper leaves of plants and severity increases.

Disease cycle: The fungus can survive on wheat during a mild winter or when covered by deep snow, or be carried in on wind currents from more southern areas as the wheat crop develops in spring.

Conditions favoring the disease: Temperatures of 60-80ºF and conditions that promote leaf wetness in the canopy for extended periods of time, such as rain, ground fog and dew increase the severity of leaf rust.

Management: The primary means of controlling leaf rust is to use resistant varieties. Scout fields from around heading to flowering. Several foliar fungicides are labeled for control of rusts. Check the label for application timing if a fungicide is used. The threshold for fungicide applications is an average 5-10 pustules/ flag leaf (averaged over 30-50 leaves). Avoid spreading the disease on clothing or farm equipment. Clothing, boots and farm equipment contaminated with rust spores should be cleaned before entering healthy fields.

Stripe rust

Cause: Stripe rust, Puccinia striiformis. (fungus) (view image)

Symptoms: Stripe rust appears as long stripes of small yellowish orange pustules on the leaves. The pustules are masses of rust spores. It can be confused with leaf rust, but the stripe rust pustules are arranged in rows, or stripes, while the leaf rust pustules are scattered on the leaf. Wheat is the only host for stripe rust.

Disease cycle: Stripe rust usually arrives in the north on wind currents from more southern wheat growing areas. It survives down south on volunteer wheat until it can infect newly planted wheat in fall and winter.

Conditions favoring the disease: Stripe rust is favored by cool, humid weather. Disease development is most rapid between 50 and 60ºF. The disease is inhibited when night time temperatures reach 65ºF or temperatures for several days in a row reach the mid 80's.

Management: The primary means of controlling both leaf rust and stripe rust is to use resistant varieties. Several foliar fungicides are labeled for control of rusts. Fungicides aren’t commonly used for stripe rust unless the disease occurs early in the season. Check the label for application timing if a fungicide is used. Avoid spreading the disease on clothing or farm equipment. Clothing or boots contaminated with rust spores should be cleaned before being worn to walk through healthy fields. Likewise, rust can spread from contaminated farm equipment. Clean contaminated equipment before using it in a field of healthy plants.

Image Captions: Leaf rust

Stripe rust

Photo credit for both: Lee Siler, MS

Growth stage limitations for applying certain fungicides

Flag leaf emergence (Feekes GS 8)	Flag leaf collar visible (Feekes GS 9)	Heading (Feekes GS 10.5)	Beginning of flowering (Feekes GS 10.5.1)
Stratego- trifloxystrobin+ propiconazole	Quilt- azoxystrobin + propiconazole	Quilt- azoxystrobin + propiconazole (wheat only)	Folicur- tebuconazole
	Propimax-propiconazole	Tilt- propiconazole
		Headline- pyraclostrobin
		Quadris-azoxystrobin

Fungicide efficacy for control of wheat diseases

Diane Brown-Rytlewski
Plant Pathology

The North Central Regional Committee on Management of Small Grain Diseases has developed the following information on fungicide efficacy for control of certain foliar diseases of wheat for use by the grain production industry in the United States. Efficacy ratings for each fungicide listed in the following table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table.

Efficacy of fungicides for wheat disease control based on appropriate application timing

Product	Fungicide(s)	Rate/A (fl. oz)	Powdery mildew	Stagonospora leaf/glume blotch	Septoria leaf blotch	Stripe rust	Leaf rust	Head scab
Headline 2.09 EC	Pyraclostrobin 23.6%	6.0 to 9.0	G^1	VG	VG	E^2	E	NR
PropiMax 3.6 EC	Propiconazole* 41.8%	4.0	VG	VG	VG	VG	VG	F
Quadris 2.08 SC	Azoxystrobin 22.9%	6.2 to 10.8	F(G)^3	VG	VG	E2	E	NR
Quilt 200SC	Azoxystrobin 7.0% Propiconazole 11.7%	14.0	VG	VG	VG	VG	VG	NR
Stratego 250 EC	Propiconazole 11.4% Trifloxystrobin 11.4%	10.0	G	VG	VG	VG	G	NR
Tilt 3.6 EC	Propiconazole* 41.8%	4.0	VG*	VG	VG	VG	VG	F
Folicur 3.6 EC^4	Tebuconazole* 38.7%	4.0	G	VG	VG	E	E	G

¹ Efficacy categories: NR=Not Recommended; F=Fair; G=Good; VG=Very Good; E=Excellent

² Efficacy may be significantly reduced if solo strobilurin products are applied after infection has occurred

3 (G) indicates greater efficacy at higher application rates.

⁴ Folicur does not have a federal label, but may have Section 18 emergency registration in some states (including Michigan).
*There may be other generic propiconazole and tebuconazole products available (check with your supplier).
This information is provided only as a guide. It is the responsibility of the pesticide applicator by law to read and follow all current label directions. No endorsement is intended for products listed, nor is criticism meant for products not listed. Members of NCERA-184 assume no liability resulting from the use of these products.

Fertilizer placement

Darryl Warncke
Crop & Soil Sciences

Placement of fertilizer in the seed furrow (pop-up) or 2 inches below and 2 inches (2x2) to the side of the seed can enhance early plant growth, especially in cool soil situations. Soils tend to warm more slowly under no-till and reduce tillage systems where there is more plant residue. At a 2x2 placement, there is minimal risk of any plant injury. Placement of fertilizer directly below the seed increases the injury, especially with limited soil moisture or with some fertilizers that may release volatile ammonia, such as ammonium thiosulfate.

Placing fertilizer with the seed (pop-up) has the greatest risk of injury, but can be done safely at low rates. The primary concern is with the amounts of nitrogen (N) and potassium (K₂O) being applied. General guidelines from several land-grant universities are to limit the total amount of N + K₂O to 5 lbs/acre for sandy soils to 10 lbs per acre for clayey soils. At 3 gallons per acre a 9-24-3 fertilizer supplies 4 lbs N + K₂O per acre and a 10-34-0 fertilizer supplies 3.4 lbs N per acre. Therefore, in sandy soils the rate of liquid pop-up fertilizer should be limited to about 5 gallons per acre, whereas in loam and clay loam soils up to about 8 gallons per acre can be used.

How much winter injury did alfalfa receive from recent low temperatures?

Richard Leep
Crop & Soil Sciences
MSU Forage Agronomist

The warm temperatures in late March may have gotten the alfalfa into trouble. Fortunately, while the weather progression from a warm, dormancy-breaking late March to a bone-chilling early April has provided reasonable cause for concern; early field observations are providing some comfort, at least for the moment.

The potential for winter injury is always difficult to predict, but we continue to try to do it anyway. Whether our predictions turn out right or wrong, perhaps there is benefit in getting us to think about it and into alfalfa fields to see how they’re progressing.

In the northern two-thirds of Michigan, recent weather has been pretty favorable for alfalfa survival. Early reports showed little if any alfalfa broke dormancy in March. And most of the northern two-thirds of the state received an insulating blanket of snow prior to the cold snap. So concerns in central and northern Michigan are largely limited to low areas where water may have pooled and frozen for extended periods during the winter, enhancing the potential for either suffocation or heaving.

In the southern third of Michigan, however, alfalfa did begin to break dormancy in late March, and while the western part of southern Michigan had insulating snow cover in early April, the eastern part did not. Healthy, well-hardened, fully dormant alfalfa is very cold tolerant; crowns and crown buds are thought to be able to withstand soil temperatures as low as 5 to 15°F. Snow cover is one of the best forms of insulation, but plant stubble/residue also helps – not just indirectly by helping to catch snow, but directly, too.

The critical low soil temperature that actively growing (fully out of dormancy) crowns can tolerate is unknown and certainly influenced by many factors. Our best guess for healthy plants is somewhere in the range of 20 to 25°F, but I’ve seen lower estimates. And alfalfa plants don’t go from fully dormant to fully out of dormancy overnight, at least from a chemical composition perspective. It’s likely that freezing tolerance is lost gradually as the plant comes out of dormancy and crown buds elongate to form legitimate amounts of herbage. Thus, plants that have little herbage development, say 1-3 inches, likely have more freezing tolerant crowns than those that are further along, say 6 inches or more. But as herbage development progresses and thus ground cover increases, crown insulation is also improved. Yet the herbage is fully exposed. Air temperatures in the low 20s can kill the growing point of shoots