April 12, 2007
In this issue
§ Soybean seed applied inoculation
§ New soybean management resources are available online
§ Management of foliar wheat diseases, Part 1
§ Challenges and options for giant ragweed management
§ Updates from the 2007 Weed Control Guide for Field Crops
§ New herbicide options in corn and soybean
§ Mark your calendars: MSU Weed Tour and Crop Diagnostic Day dates are set
§ Buildup and maintenance fertilization – reducing cost
§ Nitrogen fertilizer additives
§ New formulation of Kocide® 3000 available for 2007
§ Field crops page now available on Enviro-weather
§ Regional reports
§ Weather news: Winter blues
Nitrogen fixation is a result of the symbiotic relationship of Rhizobia bacteria and soybean plants. These bacteria fix atmospheric N2 into the NH4 form, which is useful to the plant. In return, the plant provides the bacteria with carbon photosynthesis products (dicarboxylic acids), which the bacteria use as food. Establishing rhizobia or inoculation in a field that has never grown soybean is needed to ensure nitrogen fixation. Elmore (1996) suggests when and how soybeans should be inoculated, and provides recommendations on inoculate type to use. Soybeans grown on soils without a rhizobia population will use available soil nitrogen, and if soil nitrogen levels are low because of soil type, soil erosion, etc., the symptoms of nitrogen deficiency may occur.
Field studies in
Two types of inoculants can be used: seed-applied and soil-applied. The seed-applied inoculate is more effective when mixed with water to form a slurry that is used to coat the seed. This should be done as close to planting time as possible, preferably within several hours. The soil-applied inoculate may be easier to apply than the seed-applied inoculate, but it is more expensive on a per acre basis. Thus, seed applied inoculant is generally the method of choice for most growers.
In addition to the recommended short time period between
seed applied inoculant application and planting, there are other potential challenges
associated with proper soybean seed inoculation. Care should be taken in
applying inoculant to fungicide or insecticide treated seed. Fungicide and
insecticide labeling should be checked to ensure that the particular pesticide
product is compatible with Rhizobium inoculant. Potter (2004) conducted field
trials to examine the effects of inoculating soybean seed with rhizobium, seed
applied insecticides and fungicides, and combining bacterial inoculant,
insecticidal and fungicidal products in
A three-year
View chart of Results from Soybean Inoculant/Fungicide Trials, 14 Michigan sites in soybean rotation, 2003-2005.
Finally, Rhizobia do not function below pH 5.0 and molybdenum, which is important
for Rhizobia nodule formulation, can be deficiencient at pH levels below 6.0. Liming
of low pH soils is the best solution for these challenges.
1) Inoculates should be stored in a cool place and not exposed to the sun prior to use. Refer to product labels for specific handling recommendations.
2) The safest approach is to buy fresh inoculate each year.
3) Seed should be planted within four hours of inoculation. New products are being developed with a longer preplant application interval, but data on the performance of these products is somewhat limited.
4) When applying a fungicide or using fungicide treated seed, be sure the fungicide has dried before applying inoculate to the seed. Inoculate should NOT be mixed with fungicides and applied together. Refer to product labels for specific handling recommendations
5) When loading a drill or planter using an auger, inoculation materials (liquid or dry) should be added to the seed as it enters the auger for thorough application.
6) When loading a drill or planter from bags, fill the seed box to a depth of three inches and scatter the appropriate amount of inoculate over the seed and mix it in thoroughly. Continue to add seed in six-inch deep layers, treating each until the seed box is filled.
7) With some dry materials it may be desirable to slightly moisten seed to increase the adherence of inoculate. Individual seeds need no more than a three to five percent coating of dry material. Liquid materials will usually cover most of the seed.
8) Seeding equipment should be calibrated using treated seed.
9) Lime soils used for soybean production according to soil test recommendations.
References
Beuerline, J. (2004) Soybean inoculation; its science, use, and performance. http://agcrops.osu.edu/soybean/documents/SoybeanInoculation.pdf
Elmore, R. W. (1996). Soybean Inoculation—When is it
necessary?
Potter, B. (2004). Yield effects of seed applied fungicide,
insecticide and Rhizobium inoculants on soybean.
The Soybean 2010 website has been updated to include new
soybean management information aimed at helping
Links to
other useful soybean management websites have been added to the Soybean 2010
webpage. Sources include:
The results of the 2005 Soybean 2010 grower survey are also posted on the website. The survey showed that high-yield producers used key management practices more extensively and consistently than low-yield producers. Soybean growers can use the survey results to identify management areas that may be limiting their soybean yields.
Soybean 2010 was
developed to help
The most important leaf diseases of wheat in
Leaf diseases affect yield by reducing the amount of green leaf area available to capture sunlight and make carbohydrates used during grain filling. The flag leaf is the most important in determining grain yield and quality, but heavy infections as early as the fully-tillered stage have been shown to lead to modest yield declines.
Varietal resistance is the first line of defense in
managing foliar disease of wheat.
Use the tables to view field trial ratings and determine variety performance with respect to susceptibility or resistance to a particular disease.
Cultural practices, particularly crop rotation, can serve to prevent or minimize disease development. Wheat should never follow wheat or other cereals, if at all possible. In addition, growers should avoid heavy fertilization with nitrogen as overly dense, lush stands tend to encourage leaf diseases. Planting wheat prior to the Hessian Fly Free Date may encourage the establishment of diseases such as powdery mildew and Septoria, and is an additional reason to delay planting.
Fungicide application may be profitable when there is severe disease pressure, and a susceptible variety has been planted. Fungicide research trials have shown that under low to moderate disease pressure, many wheat varieties may not show an economic return when treated with fungicides. Foliar fungicides protect yield when disease pressure is severe. The best candidates for fungicide treatment are fields with the highest yield potential. Before using a foliar fungicide, growers should determine the yield potential of the wheat crop, and the straw, if it is to be marketed, and determine whether applying a fungicide is likely to be profitable. Management practices targeted toward specific diseases are listed under the specific disease headings.
Scouting individual
fields is critical to making sound management decisions. Inspect
fields for disease before making a decision to apply fungicides. Check about 30
to 50 tillers randomly in the field to get a clear picture of the extent of
disease present; avoid looking in just one or two locations.
Cause: On wheat- Erysiphe graminis f.s tritici (fungus). On
barley- Erysiphe graminis f.s. hordei (fungus). These fungi are host specific.
Symptoms: Powdery, white to light gray patches may appear on leaves
and stems (especially upper leaf surfaces) any time after seedlings
emerge. Black specks containing spores may form in the patches of mildew as the
season progresses.
Powdery mildew overwinters as resting spores on straw,
stubble, volunteer or overwintering wheat.
Conditions favoring the disease: Cool temperatures (59 to 72ºF) and high humidity
(greater than 85%) are optimal for the development of the disease. Heavy
nitrogen fertilization also enhances disease development.
Management: Select resistant varieties. Avoid heavy amounts of
nitrogen, which can stimulate rapid growth. Determine the need for fungicide
treatment by scouting for powdery mildew
at flag leaf emergence and the boot stage. The threshold is an average two to
three spots per leaf (averaged over 30 to 50 leaves) on the leaf below the flag
leaf.
Causes: Septoria tritici and Stagonospora
nodorum. (fungi).
Symptoms: The first symptoms are tiny yellow flecks on the lower leaves. Septoria
expands to angular, tan to brown lesions containing black, pinpoint specks
(pycnidia, which produce spores). It does not infect the glumes. Stagonospora
lesions are lens-shaped with yellow halos and may contain brown pinpoint specks
(pycnidia) within the lesions. Stagonospora affects both leaves and glumes.
On wheat heads, it starts as gray-brown spots on the chaff that become dark
brown blotches with grayish-white centers on the glume.
Conditions favoring the disease: These fungi overwinter on straw, living
plants or seed. Spores are present in late summer and fall, and can germinate
over a wide temperature range. Spores are produced during periods of wet
weather and can cause infections throughout the growing season.
Barley is generally less susceptible than wheat. Wet and windy weather
favors the development of the disease. Septoria is more prevalent
earlier in the season (at temperatures around 50-68°F), during the period from
stem elongation to flag leaf emergence. Stagonospora tends to appear
around heading (temperatures are in the 68-81°F range). Cool, wet weather
during flag leaf emergence provides favorable conditions for severe outbreaks
of this disease. Planting small grains as successive crops allows inoculum to
build up in the field, especially under no till or minimum tillage.
Management: Select varieties with resistance. Use certified seed. Seed treatment may help limit seedborne disease. Rotate out of small grains for two years. Avoid planting into wheat stubble. Determine the need for fungicide treatment by scouting at flag leaf emergence and the boot stage. The threshold is an average one to two lesions per leaf (averaged over 30-50 leaves) on the leaf below the flag leaf.
Giant ragweed is an early germinating, summer annual weed
species that is commonly found throughout the southern two tiers of
Giant ragweed is potentially the most competitive weed
species in
Historically, giant ragweed was found mostly in undisturbed areas such as fencerows and drainage ditches, and could occasionally be found in flood-plain fields. However, in the last couple of decades giant ragweed populations have dispersed from their primary habitats into many fertile fields across the state. The cause of this spread is unknown. However, it is clear that giant ragweed has adapted to survive new agronomic practices such as earlier planting and less tillage.
One adaptation that giant ragweed has made has been a shift
in the time of emergence. Historically,
giant ragweed plants would emerge early in the growing season and normally
would not be a problem in agronomic production systems. Results from
Effective control of giant ragweed has relied heavily on the
use of herbicides. In soybean there are
fewer herbicide options for controlling giant ragweed than in corn. Prior to the wide-spread use of Roundup Ready
soybean, ALS-inhibiting herbicides such as FirstRate and Classic were used
extensively for giant ragweed control.
The extensive use of these herbicides resulted in the development of
ALS-resistant giant ragweed populations.
ALS-resistant giant ragweed populations have been confirmed in several
production fields in
For several years glyphosate has been an extremely effective
herbicide for controlling giant ragweed in both Roundup Ready corn and
soybeans. However, recently giant
ragweed has been harder to control with glyphosate. Too low herbicide rate on large giant ragweed
plants, giant ragweed emergence after herbicide application, and inadequate
herbicide coverage may explain some of these control failures. However, more recently researchers in
There are a number of very effective herbicides available for controlling giant ragweed; however control with these herbicides can be rather inconsistent. Giant ragweed can escape control from soil-applied herbicides by germinating from considerable depths and emerging later in the season where a soil-applied herbicide may have already dissipated. Inconsistencies with postemergence herbicide programs are usually attributed to giant ragweed’s considerable growth rate. Often times giant ragweed may already be too large when the postemergence application is made, allowing for the plant to regrow after the treatment. In addition, with the shift in giant ragweed emergence some of the plants may emerge after the postemergence application has already been made. Another caveat to add to the lack of giant ragweed control is the development of resistant populations to ALS-inhibitors and now to glyphosate has limited the use of some very effective herbicides in some areas. To overcome these different challenges the most consistent giant ragweed control programs are those that combine a sequential management approach. These include the use of both preemergence (PRE) and postemergence (POST) herbicide applications.
To manage giant ragweed in corn and soybean the most effective giant ragweed programs should include the following steps:
§ Control weeds that emerge prior to planting with tillage or preplant burndown applications.
§ Apply PRE herbicides with activity on giant ragweed to reduce competition with crops, provide flexibility in the timing of POST applications, and reduce the need for additional POST glyphosate applications.
§ Where a PRE herbicide is used with giant ragweed activity apply POST herbicides before plants are 6 to 10 inches tall. If a PRE is not used, apply when giant ragweed is less than 6 inches tall. With non-glyphosate herbicides, applications should be made prior to 4-inches tall.
§ Scout fields two weeks after the POST application. Control escapes or plants that emerge after the initial POST application with a second POST application.
Sequential management programs (PRE followed by POST) are essential for controlling giant ragweed in soybean.
No-till
burndown programs:
§ Most effective burndown herbicide applications include the use of 2,4-D ester (1 pt/A) with glyphosate or Gramoxone Inteon. The addition of a residual herbicide that contains chlorimuron (Canopy, Synchrony, or Valor XLT) or cloransulam (FirstRate, Gangster, Sonic, or Authority First) can improve and will provide residual control of giant ragweed populations that are not ALS-resistant. Applications including 2,4-D ester should be made 7 days prior to planting soybeans, also be aware of county restrictions in areas where grapes are grown.
§ Avoid using glyphosate, Gramoxone Inteon, or 2,4-D ester alone, since control is likely to be less consistent than with combinations.
§ Higher glyphosate application rates should be used when plant exceed 6-inches in height.
PRE soybean herbicides (conventional-till
soybeans):
§ Apply a PRE residual herbicide that contains chlorimuron (Canopy, Synchrony, or Valor XLT) or cloransulam (FirstRate, Gangster, Sonic, or Authority First) to provide initial residual control of giant ragweed populations that are not ALS-resistant.
§ These herbicides will not provide season-long giant ragweed control.
POST soybean herbicides:
§ Roundup Ready soybeans: Glyphosate and glyphosate products will provide good to excellent control of giant ragweed. Higher glyphosate rates 1.1 (less than 6-inch tall giant ragweed) to 1.5 lb ae/A will be more effective.
§ ALS-inhibitors: FirstRate is the most effective ALS-inhibitor for control of giant ragweed. Raptor and Classic will provide good control of small giant ragweed. These herbicides will not control ALS-resistant giant ragweed populations.
§
Diphenyl ether herbicides: Flexstar, Reflex,
Cobra, or
Similar to giant ragweed control in soybeans, sequential management programs (PRE followed by POST) are the most effective for control of giant ragweed. However, under light giant ragweed populations total PRE programs may provide adequate giant ragweed control.
Total
PRE programs (low populations only):
§ Combine atrazine-containing products (i.e., Harness Xtra, Bicep II Magnum, Guardsman Max, Keystone, etc.) with Hornet or Callisto.
§ The premixes Lumax or Lexar (atrazine + Callisto + s-metolachlor) may also be used.
PRE followed by POST programs (moderate to
high populations):
§ PRE: Apply products that contain atrazine, Hornet, or Callisto.
§
POST:
There are several POST products in corn that effectively control giant
ragweed. These herbicides should be
applied before giant ragweed is 4-inches tall.
§
Atrazine, Buctril, and Callisto all provide good
control of giant ragweed.
§
A combination of atrazine + Callisto or Buctril
+ atrazine will provide greater control of giant ragweed than anyone of these
herbicide applied alone.
§
Plant growth regulator herbicides: 2,4-D amine will provide good control of
giant ragweed. Clarity, Distinct,
Status, Stinger and Stinger premixes (Hornet) will provide excellent control of
giant ragweed.
§
ALS-inhibitors: Beacon and Spirit provide
excellent control of non-ALS-resistant giant ragweed.
§ Roundup Ready corn: Glyphosate will provide good to excellent control of giant ragweed. Higher glyphosate rates 1.1 (less than 6-inch tall giant ragweed) to 1.5 lb ae/A will be more effective.
§
Liberty Link corn:
It is important to consider control of other weeds, soil pH restrictions, rotations restrictions, and maximum allowable rates (i.e., atrazine) when designing a giant ragweed management program. If giant ragweed is not currently a problem in your fields, make sure to keep a watch out for those giant ragweed populations in undisturbed areas, such as fencerows, roadsides, and waterways. These areas can often times be the source of seeds to spread into fields.
(Editor’s note: View
the guide on the Internet at: http://www.msuweeds.com/publications/2007_weed_guide/.
You can also purchase a guide from your
The 2007 Weed Control
Guide provides the latest up-to-date information on weed management
recommendations in corn, soybeans, small grains, forages, dry edible beans,
potatoes, sugar beets, and sorghum. Other features include: an up-to-date table
on the current glyphosate products that are labeled for use in
There are three new herbicides added to the corn section of the Weed Control Guide in 2007. They were Impact (p. 29), Resolve (p. 25 & 40) and Stout (p. 39).
Impact 2.8SC (topramezone)
is a new postemergence herbicide for the control of most broadleaves and has
some suppression of grasses. It is a
“bleacher” herbicide that can be used on all types of corn including seed and
sweet corn (Check with the seed corn companies before applying it to parent
inbred lines.). The use rate recommended
for
Resolve 25DF (rimsulfuron) is a compound that has been used in combination with other herbicides (Basis, Steadfast and Accent Gold) for several years. It has also been used in potatoes and tomatoes under a different name, Matrix. Resolve can be applied preemergence or postemergence on field corn only for the control of many grasses and some broadleaves. The recommend rate for either a preemergence or postemergence application timing is 1.0 oz/A. The addition of ¼ to ½ lb of atrazine postemergence will improve the overall weed control of Resolve. Non-ionic surfactant and ammonium sulfate are needed for effective post emergence weed control.
Stout 72.5DF is a new mixture of two herbicides, Accent (nicosulfuron) and Harmony GT (thifensulfuron). Stout is a postemergence herbicide for the control most grasses and a few broadleaves. The application rate for Stout is ¾ oz/A. Crop oil concentrate and 28% liquid nitrogen are needed for effective weed control.
The soybean section of the 2007 Weed Control Guide has been expanded to include new information on weed control options in no-till soybean (p.76-79). This section offers information on the burndown and residual activity of various herbicides and herbicide combinations. Additional information on fall herbicide applications has also been included. Five new herbicide names appear in the soybean section of the 2007 Weed Control Guide: Prefix CP (p. 58), Canopy 75DF (p. 51 & 77), Authority First (p. 60 & 77), Sonic (p. 60 & 77), and SelectMax 1EC (p. 72). Several of these herbicides are not new to the marketplace. In fact, none of these new products contain new active ingredients.
Prefix CP is a new co-pack of Prefix (s-metolachlor) and Reflex (fomesafen) that is manufactured by Syngenta Crop Protection and registered for preplant and preemergence weed control in soybean. Typical application rates of Prefix CP are 1.1 pt/A of the Prefix component and 1 pt/A of the Reflex component. Prefix CP will provide 4 to 5 weeks of residual weed control and should only be used as a foundation herbicide prior to a postemergence herbicide application in a sequential weed control program. Weeds that are controlled in the initial 4 to 5 weeks after application include: excellent control of eastern black nightshade, pigweeds, wild mustard and most annual grasses and good control of common lambsquarters, common ragweed, and smartweed. Prefix CP should be applied with a burndown herbicide like glyphosate, 2,4-D ester, and/or Gramoxone to control weeds that have emerged prior to Prefix CP applications in no-till soybean. Restrictions and precautions for Prefix CP are similar to restrictions for s-metolachlor (Dual Magnum) and Reflex.
Canopy 75DF is
a premix formulation of chlorimuron (Classic) and metribuzin (Sencor) that can
be applied in the fall, early preplant, preplant incorporated, or preemergence.
Canopy is a replacement for Canopy XL for burndown and preemergence
applications in soybean. Canopy’s
labeled application rates range between 2.25 and 7 oz/A, however typical
Authority First and Sonic 70DF are two new premixes for preplant, preemergence or preplant incorporated use in soybean. Authority First is marketed by FMC Corporation and Sonic is marketed by Dow AgroSciences. Both of these products contain the same active ingredient at the same ratio, 62.1% of sulfentrazone (Spartan) and 7.9% of cloransulam-methyl (FirstRate). The typical use rate for these herbicides is 3.2 oz/A when used as foundation herbicide prior to a postemergence application in a sequential weed control program and 6.4 oz/A for use in a total preemergence only program. Authority First or Sonic should be applied with a non-ionic surfactant plus ammonium sulfate (AMS) or crop oil concentrate plus AMS in no-till soybean to control weeds that have emerged prior to preemergence application. Glyphosate and/or 2,4-D ester should be included to control a broader spectrum of weeds. Authority First or Sonic should not be applied after soybeans have emerged. Excessive rainfall immediately after application may cause soybean stunting. Weeds that are controlled by Authority First or Sonic include: excellent control of c. ragweed, pigweeds, smartweed, and wild mustard and good control of jimsonweed, common lambsquarters, giant ragweed, velvetleaf and eastern black nightshade.
SelectMax 1EC is a new formulation of clethodim being manufactured by Valent that contains a built-in adjuvant package. This new formulation increases the flexibility in adjuvants that can be used when applying clethodim for postemergence grass control. Preferred adjuvant choices still include a crop oil concentrate or methylated seed oil at 1% v/v (but not less than 1 pt/A); however a non-ionic surfactant at 0.25% v/v can be used for certain tank-mixtures. The addition of ammonium sulfate at 2.5 to 4 lbs/A may be added to improve control of difficult to control weeds. The typical use rate for SelectMax is 9 fl oz/A. To control volunteer corn (4 to 12 inches tall) SelectMax should be applied at 6 fl oz/A. For tank-mixtures with glyphosate products specifically for control of volunteer Roundup Ready corn in Roundup Ready soybeans ammonium sulfate should be included at 17 lbs/100 gallons of spray solution plus additional adjuvants that are recommended on the glyphosate label.
There were three new herbicides added to the wheat and small grains section of the Weed Control Guide in 2007. They were Affinity BroadSpec (p. 92), WideMatch (p. 93) and Osprey.
Affinity BroadSpec 50DS is a new combination of Harmony GT (thifensulfuron) and Express (tribenuron) that provides similar control for most weed species controlled by Harmony Extra. The major difference between Harmony Extra and Affinity BroadSpec is that Affinity BroadSpec is a 1:1 ratio of Harmony GT and Express that translates to a lower relative cost per acre. The use rate for Affinity BroadSpec is 0.75 oz/A. Adjuvants are needed and will depend on tank mix partners.
WideMatch 1.5L is a premix combination of Stinger (clopyralid) and Starane (fluroxpyr) for broadleaf weed control up to the boot stage in wheat, barley and oat without a legume underseeded. The recommended application rate is 1.0 to 1.33 pt/A.
Osprey 4.5WDG (mesosulfuron) is a postemergence herbicide for the control of most grass and some broadleaf weed species in winter wheat. Osprey can be particularly useful for controlling annual bluegrass, annual ryegrass and windgrass along with a few broadleaf weeds. The use rate of Osprey is 4.75 oz/A and requires the addition of adjuvants for effective weed control. The type and rate of the adjuvants will depend on tank mix partners.
Two new herbicides were added to the dry edible bean section for the 2007 Weed Control Guide: SelectMax (p. 121) and Reflex (p. 119). SelectMax is described in the soybean section above.
After over 10 years of Section 18s, Reflex 2L (fomesafen) has finally received full federal
registration for use in dry beans.
Recommendations for Reflex use in dry beans can now be found in the weed
control guide. Reflex has been an
important tool for
The addition of SelectMax was the only change in the potato and sugar beet sections for the 2007 Weed Control Guide. SelectMax is described in the soybean section above.
Since the release of the 2007 Weed Control Guide for Field Crops, several new herbicides have
been registered for the 2007 growing season in corn and soybean. Following is information on some of the new
products you will hear about this season.
New registrations or label changes that occurred prior to publishing the
Weed Control Guide can be found in the previous article, Updates from 2007 Weed Control Guide for Field Crop.
Breakfree, Breakfree ATZ and Breakfree ATZ Lite are a group of preemergence/early postemergence
herbicides that are similar to Surpass, Keystone and
Status is a new
formulation of Distinct (dicamba + diflufenzopyr) that includes a crop safener
for postemergence control of broadleaves.
This safener increases the metabolism of the herbicide inside the corn
plant resulting in a decrease in the potential for injury due to an extreme
wind event. The recommended use rate for
Status alone is 5 oz/A or 2.5 oz/A if tank mixed another herbicide like
glyphosate. The preferred adjuvant for
Status is crop oil concentrate, however if tank mixed with an adjuvant-loaded
glyphosate, no adjuvant is needed.
Status can also be tank mixed with herbicides that require non-ionic
surfactant or methylated seed oil adjuvants.
Although Canopy EX (29.5 DG) is not a new herbicide to the soybean market, recent label changes will allow for it to be used differently that it has in the past. Canopy EX is a premixture of Classic (chlorimuron) plus Express (tribenuron) that has been typically used in the fall or early spring (45 d prior to planting) for control of winter annual weeds and residual control of certain summer annual weeds. Canopy EX can now be applied within 7 d of planting soybean if the use rate is 2.2 oz/A or less and can be applied within 14 d of planting with use rates of 2.2 to 3.3 oz/A. As with all chlorimuron products use rates and rotational restrictions are dependent on soil pH.
Valor XLT 40.3DG is a new premixture being marketed by Valent Agricultural Products. Valor XLT contains Valor (flumioxazin) and Classic (chlorimuron) and can be applied in the fall, early preplant, preplant, or preemergence. The typical use rate of Valor XLT is 3 oz/A (1.76 oz/A of Valor and 1.24 oz/A of Classic), unless the soil pH is greater than 6.8. If the soil is pH ranges from 6.9 to 7.6, Valor XLT should only be applied at 2.25 oz/A or less. DO NOT use Valor XLT if soil pH is greater than 7.6. Valor XLT will provide control of some winter annual weeds and provides residual control of common lambsquarters, common ragweed, eastern black nightshade, pigweeds, smartweed, velvetleaf, wild mustard and horseweed (marestail). Valor XLT should not be applied to emerged soybeans and should not be tank-mixed with chloroacetamide containing products like: s-metolachlor (Dual Magnum), dimethenamid-P (Outlook), alachlor (Intrro), or flufenacet (Define) or severe soybean injury can occur. Rotational restrictions and precautions for Valor XLT are similar to restrictions for Valor and other chlorimuron containing products.
Before you schedule your vacation this summer, make sure to get these two dates on your calendar. The 2007 MSU Weed Tour will be held on Wednesday, June 27 and the Fifth annual MSU Crop Diagnostic School will be held on Tuesday, July 10. These field days offer you the latest information in weed management and other crop protection and crop management strategies. Stay tuned to future CAT Alerts for details and registration forms for each of these events.
Good news, the price for corn, soybeans and wheat went up significantly since 2006. This is a result of the high demand for corn to produce ethanol and many other products. Corn acreage for 2007 is predicted to increase greatly, which increases the demand for fertilizer nutrients. Hence, the bad news, fertilizer prices have increased greatly, especially nitrogen. In a separate article, Dr. Gehl is addressing nitrogen fertilization of corn. This article will focus on phosphorus (P) and potassium (K) fertilization.
Recommendations from MSU for P and K include; a portion to build up the soil to a critical level (CL), which corresponds closely to the soil test value where 95 percent of maximum crop yield is attained, and a portion for maintenance, which is equal to crop removal. Depending on the price ratio of the crop to the fertilizer nutrient, the CL may also be close to the point of maximum economic yield. For corn and soybeans, the CL soil test is 15 ppm P, and for wheat and alfalfa the CL value is 25 ppm. The adequate soil test P range is 15 ppm above the CL, or is 15 to 30 ppm for corn and soybean, and is 25 to 40 ppm for wheat and alfalfa. For K the CL value varies with soil texture (as indicated by the CEC, cation exchange capacity). The adequate range is 20 ppm above the CL value for most field crops.
The long term goal is to maintain the P and K soil test values in the adequate range. The soil test P or K value can be maintained in the adequate range by applying an amount of phosphate or potash that is equal to what is removed in the harvested portion of the crop. Table 1 indicates the amount of P and K removed in each harvested unit for selected crops.
If the soil test P or K value is below the CL value, then an additional amount is recommended to build the soil test value up to the CL value over a four-year period. If the budget is tight and choices must be made on how to spend resources for inputs, the fertilizer bill can be reduced by one of the following approaches. When the soil test value is below CL (in the buildup zone), apply only the maintenance amount of P or K. When the soil test value is in the adequate range, reducing the amount applied should not adversely affect crop yield, but will result in a decrease in the soil test level.
Applying 20 lbs less P2O5/acre than crop removal may result in a decrease in the soil test P value of about 2 ppm in sandy soils, 1 ppm in loam soils and 0.5 ppm in clayey soils. For each 20 lbs K2O/acre less than crop removal applied, the soil test K may be expected to decrease about 4 ppm, 3.3 ppm and 2.8 ppm, respectively, in soils with CECs of 5, 10 and 15 me/100 grams.
The following are three examples of how these approaches work.
Example 1. Soil test P value is 25 ppm (adequate range), corn is being grown and the yield potential is 200 bu/acre. The maintenance recommendation is 74 lbs P2O5/acre (200 x 0.37). Applying 30 lbs P2O5/acre in a band at planting will get the crop off to a good start and reach the yield potential, and the fertilizer bill will be reduced by the cost of 44 lbs P2O5/acre (~$12/a).
Example 2. Soil test P value is 10 ppm so the recommendation for 200 bu corn is 99 lbs P2O5/acre (25 for buildup and 74 for crop removal). Applying only crop removal (74 lbs P2O5/acre) will be enough to reach the yield potential and will save the cost of 25 lbs P2O5/acre (~$7/a).
Example 3. Soil test K value is 30 ppm below the CL value (105 ppm) in a soil with a CEC of 12. K2O recommendation for 200 bu/a corn is 102 lbs K2O/acre (48 + 54). Applying only crop removal (54) will save the cost of 48 lbs K2O/acre (~$12/a).
Table
1. Nutrient removal in harvested portion of selected crops.
Crop Unit
-----------lbs/unit------------
Alfalfa ton 45 13 50
Corn grain bu 0.9 0.37 0.27
Corn silage ton 9.4 3.3 8.0
Soybean bu 3.8 0.8 1.4
Sugar Beet ton 4.0 1.3 3.3
Wheat bu 1.2 0.63 0.37
*Values for other crops are in Table 3 of MSU
Extension Bulletin E-2904.
The escalating prices of N fertilizers and concerns regarding N fertilizer supplies have many producers questioning the potential benefits of N fertilizer additives, particularly nitrification and urease inhibitors. Extensive research on these types of products has been conducted throughout the North Central region for many years, with results generally indicating that effectiveness is reliant on many factors, including N source, timing, soil type and tillage. In years past, a somewhat common practice was for growers to apply a little extra N as a relatively cheap form of insurance. However, with high N fertilizer cost many growers are looking for alternative strategies to assure adequate N is provided to the growing crop.
The primary objective of urease inhibitors is to reduce the potential volatilization losses of urea-based fertilizers. When urea is applied to soil, it must be converted through hydrolysis (addition of water) to the ammonium form before it becomes plant available. This conversion is driven by an enzyme called urease, which is abundant within the soil. When urea is applied and incorporated or rained into the soil, the breakdown of urea to the ammonium N form will occur in about 2 to 3 days. If urea is surface applied and not incorporated within 2 to 3 days, urea can be converted first to ammonium and subsequently to ammonia, which is susceptible to volatilization loss. Nitrogen losses due to volatilization can be in excess of 20% of the applied N, and are typically the greatest where there is a relative high surface soil pH, high amounts of surface residue, and in warm and windy weather conditions. Urease inhibitors are applied to interfere with the urease enzyme, and essentially delay the hydrolysis of the urea molecule, typically for 10 to 14 days.
Most university research to date has focused on the urease
inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), which is sold under the
trade name Agrotain. Research results
have indicated that NBPT can be effective at reducing volatilization losses and
enhancing yields, though consistent responses should not be expected every year
or on all fields. Hendrickson (1992)
summarized nationwide research regarding the effects of NBPT use for surface
applied urea and UAN. The summary
included data from 78 experiments in 17 states (including
Table
1. Summary of corn yield increases from
application of NBPT with surface applied urea and UAN (Hendrickson, 1992).
Yield increases were significant (P<0.01).
|
|
|
Yield increase |
|
|
Experiment sites |
Number of sites |
Urea |
UAN |
|
|
|
- - - - - - bu/ac - - - - - - |
|
|
All sites |
78 |
4.3 |
1.6 |
|
N responsive sites* |
64 |
5.0 |
2.8 |
|
Sites with significant ammonia loss |
59 |
6.6 |
2.7 |
|
*Sites where yield increased when N fertilizer was applied |
|||
So where are urease inhibitors most likely to pay off? If urea or urea-based fertilizers are surface applied and not incorporated, a practice typical of no-till cropping systems, the chance for volatilization losses is most significant. Cropping systems/tillage practices that result in relatively high surface residues will promote volatilization, as will recent unincorporated lime applications. The amount of N loss through volatilization will depend on whether adequate rainfall (about 0.25”) or mechanical incorporation occurs within a few days of application. If adequate rain comes, volatilization losses will be minimized and money spent on a urease inhibitor may not be recovered in N savings and yield increases. But, if the urea is not moved into the soil soon after application, the effectiveness of the urease inhibitor will be enhanced. At about $50/gal, applied at a rate of 5 qt/T of urea, the additional cost of a urease inhibitor would be about $0.07 per pound of actual N. When deciding whether to use this type of product, growers should evaluate their cropping system and determine whether the risk of N loss is worth the extra input cost. If conditions are favorable for N loss, use of NBPT can help prevent N (and yield) losses, but positive responses should not be expected every year.
Nitrification is a microbial soil process by which N in the ammonium form is converted to nitrate. Soil N as ammonium is held on soil cation exchange sites and is relatively stable, in terms of loss, while nitrate-N is highly susceptible to losses by leaching or denitrification. Leaching losses are especially pronounced in coarse textured soils that receive excess water while denitrification occurs in warm (>50◦F), wet conditions primarily on fine textured soils, though both these processes can occur on some level regardless of soil texture.
When conditions are favorable for these loss mechanisms, it
is desirable for N in the soil to remain in the ammonium form until the time of
rapid crop demand. Nitrification
inhibitors delay the conversion of ammonium to nitrate by interfering with the
metabolism of Nitrosomonas
bacteria. Common nitrification
inhibitors include nitrapyrin (N-Serve) and dicyandiamide (DCD/Guardian), which
are typically effective for 3 to 6 weeks depending on soil and climate
conditions. With fall N applications
(not recommended for MI), nitrification inhibitors may delay conversion to nitrate
until soil temperature drop low enough (below 40◦F) to limit
denitrification risks. With spring N
applications, the inhibitors keep soil N in the ammonium form until peak crop
demand (for corn, about the 6-8 leaf stage).
As with urease inhibitors, many years of research have been conducted
evaluating the effects of nitrification inhibitors on various crops and
cropping systems. Work in
Table
2. Four year average effect of N timing and N-Serve on corn yield at
|
N Timing |
N-Serve |
Yield |
Income |
N Cost |
N-Serve Cost |
Return |
|
|
|
bu/a |
$/a |
$/a |
$/a |
$/a |
|
PP |
No |
116 |
406 |
63 |
|
343 |
|
SD |
No |
134 |
469 |
63 |
|
406 |
|
PP |
Yes |
121 |
424 |
63 |
8 |
353 |
|
SD |
Yes |
134 |
469 |
63 |
8 |
398 |
140 lb N/a applied spring preplant (PP) or sidedressed (SD). N-serve applied at 2 pt/a.
Calculations based on $3.50/bu corn, $0.45/lb N, and $32/gal of N-Serve.
A report by Hoeft, 1984, summarizing results of research in many states, showed yield and return benefits of N-Serve for fall-applied N, but no benefit when N was applied in the spring. Results from that study also demonstrate a clear economic benefit to spring N applications compared with fall applications. (See Table 3)
Table
3. Effect of time and rate of N
application and N-Serve on corn yield in
|
|
|
- - - Yield - - - |
|
|
- - - Return - - - |
||
|
N Rate |
N-Serve |
Fall App. |
Spring App. |
N Cost |
N-Serve Cost |
Fall App. |
|