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March 25- April 1, 2002
C.O.R.N. 2002-6
In This Issue:
A) Corn Profit Tips-Nutrient Needs
B) Use Of 2,4-D Preplant To Soybeans - Labels Vary
C) Weed Control In Wheat
D) Winter Annual Weed Control In Late March And Early April
E) Spring Has Sprung-Weeds Emerging
F) Preplant Nitrogen For Corn
Base nitrogen (N), phosphorus (P), and potassium (K) recommendations on yield potential. Thus, a realistic yield goal is the first critical step in nutrient management. For N, observe all credits for previous crops and manure. If the previous crop was soybeans, a N credit of 30 lbs/acre may be taken. Depending on population density, perennial legumes, established more than one year, may have N credit between 40 and 140 lbs/acre. Grass sod/pastures (set-aside program) also may receive a 40 lb/acre N credit. Manure credits may be taken, depending upon application method and time of application.
A split application of N (at planting and sidedress) is the most efficient method for N management. This system allows later adjustments to nitrogen rates depending on the growing season. Fall N applications are the least efficient for N management. For fall applications, only well-drained soils should be considered, and the N material should be anhydrous ammonia with a nitrification inhibitor. A nitrification inhibitor should also be used with anhydrous ammonia-N on early preplant applications for wet soils. Incorporating or applying N in bands may minimize losses. Fertilizers with urea-N are susceptible to volatilization losses unless incorporated.
Phosphorus and potassium are relatively immobile in the soil (what a crop has not removed will generally accumulate for future crops). A soil test is the best way to determine if P and K levels are in excess, adequate, or deficient. Soil P levels above 40 ppm (80 lbs/acre) are in excess and should not need additional amounts. Phosphorus applications should match crop removal if soil levels are 15 to 30 ppm (30 to 60 lbs/acre). Crop removal rates equal the yield goal multiplied by 0.35. Between 30 to 40 ppm, amounts less than crop removal would be recommended depending on yield goals. If P soil levels are below 15 ppm, then applications would include crop removal and a buildup program.
Potassium recommendations follow the same philosophy as P, except consideration is given for soil cation exchange capacity (CEC). Since applied K may be held more tightly by soils with high CEC, rates increase as the soil CEC increases. Regardless of CEC and yield goals, yields would not respond to additional K at soil levels above 200 ppm (400 lbs/acre). Corn grown on soils that have a CEC < 10 would not respond to additional K when the soil test level > 150 ppm (300 lbs/acre). These fertilizer recommendations are available on line at: http://ohioline.ag.ohio-state.edu/e2567/index.html.
Avoidance of injury to soybeans is based on the lack of water solubility of ester formulations, which limits downward movement into soil, and the relatively rapid degradation of 2,4-D in soil. These are generally considered to be conservative recommendations, especially with regard to the 30-day restriction for the 1 lb rate.
Use of 1 lb of 2,4-D ester less than 30 days before planting, while not permitted by most labels, would improve control of many broadleaf weeds. These include marestail, dandelion, purple deadnettle, prickly lettuce, cressleaf groundel (golden ragwort), Atriplex, Pennsylvania smartweed, and large ragweeds. As far as we know, there is only one 2,4-D ester product that allows use of more then the 0.5 lb rate less than 30 days before planting.
The label for Weedone 650, a 6 lb per gallon 2,4-D ester formulation, recommends the following with regard to preplant use in soybeans: rates up to 2/3 pint (0.5 lb) per acre must be applied at least 7 days before planting; and rates higher than 2/3 pint but not exceeding 1 1/3 pints (1 lb) must be applied at least 15 days before planting. The rates allowed by this label in the 15 to 30 day before planting window should improve control of tough broadleaf weeds, especially when glyphosate is not included in the burndown herbicide mix.
The higher rates of Weedone 650 should be beneficial in combination with residual herbicides such as Sencor, Domain, Canopy XL, Boundary, Python, Valor, etc, which are often applied more than 15 days before planting without glyphosate. As always, be sure to follow label directions for use to avoid soybean injury.
Wheat as a rule is very competitive with weeds and some wheat fields do not require herbicide treatment. However, other fields can benefit greatly from herbicide application. Failure to scout fields and take the appropriate measure can result in yield loss and harvesting problems. The weeds that appear above the wheat canopy late in the season, such as ragweeds and Canada thistle, can often be easily controlled with a spring herbicide treatment.
The most common weeds observed in wheat fields at this time of year are winter annuals, such as chickweed, purple deadnettle, field pennycress, shepherd's-purse, and marestail and wild garlic. The winter annual weeds can interfere with the early spring development of wheat, and should be controlled as soon as possible to avoid interference with wheat growth. Winter annuals are more easily controlled when small and still in the rosette stage, before the stem has bolted. 2,4-D will control most mustard species (field pennycress, etc.) and marestail adequately, and can be mixed with dicamba to broaden the spectrum of control somewhat. Harmony Extra will generally be a more effective choice for control of deadnettle and chickweed.
Many wheat herbicides have some activity on Canada thistle and can suppress it enough to prevent harvest problems. Effectiveness often depends upon the size of the thistle at the time of application - regrowth is more likely when thistles are very small at time of application. Best products for thistle control are Stinger, Curtail, and Express. Best products for wild garlic are Harmony Extra, Harmony GT, and Peak, which should be applied when garlic has 2 to 4 inches of new growth but is less than 12 inches tall. Dandelion is most effectively controlled/suppressed with Curtail, but can also be suppressed with 2,4-D or a mix of 2,4-D + dicamba.
When wheat has not yet reached the jointing stage, any herbicide labeled can be safely applied. As wheat growth stage advances past jointing, and then past boot stage, herbicide choices become much more limited. At this time, wheat appears to be more advanced in growth stage compared to previous years. Most herbicides can be applied in nitrogen fertilizer solution when the wheat is top-dressed. This may increase injury somewhat, and some labels recommend adjusting surfactant rates to minimize injury. Where nitrogen is split-applied, risk of herbicide injury may be reduced if applied in a mix of nitrogen solution and water. Some key herbicide limitations are listed below - these are also shown in a figure on page 108 of the 2002 OSU Weed Control Guide and in the text on pages 100-107 or http://ohioline.ag.ohio-state.edu/b789/index.html.
2,4-D: all 2,4-D products are labeled for application before jointing. A few are labeled up to early boot stage. 2,4-D is generally safe up to early boot, but the risk of injury increases after jointing. To minimize the risk of injury after jointing, use water as the carrier and do not apply more than 1/2 pint of ester or 1 pint of amine. 2,4-D will not control chickweed or henbit, and can be weak on smartweed and deadnettle. MCPA products have characteristics and labeling similar to 2,4-D products.
Banvel/dicamba: Apply before jointing. Not as effective as 2,4-D on mustard species, but more effective on smartweed. Weak on chickweed, deadnettle, henbit, and wild garlic. Can be tank mixed with 2,4-D.
Buctril/Moxy: Apply before the boot stage. Applying in fertilizer solution increases leaf burn. Weak on most winter annuals, dandelion, and wild garlic. For best results apply before weeds reach the 4-leaf stage or a height of 2 inches.
Curtail: premix of 2,4-D plus Stinger. Apply up to 2 pints before jointing, and up to 1.5 pints before boot stage. Excellent control of ragweeds and Canada thistle, and most effective wheat herbicide on dandelion. Weak on chickweed, henbit, and wild garlic. Do not plant double crop soybeans in fields treated with Curtail.
Harmony Extra: Apply before flag leaf is visible and when weeds are less than 4 inches tall or across (rosette). Apply with nonionic surfactant. Effective for wild garlic (at high rates) and most winter annuals. Weak on ragweeds and ALS-resistant marestail.
Harmony GT: Similar to Harmony Extra, but less effective on Canada thistle, chickweed, and a few other winter annuals.
Express: Apply before the flag leaf is visible when weeds are less than 4 inches tall or across (rosette). Not as broad spectrum as Harmony Extra, but more effective on Canada thistle. Apply with nonionic surfactant.
Peak: Apply before 2nd node is detectable in wheat stem elongation, and when weeds are 1 to 3 inches tall. Do not plant double crop soybeans in fields treated with Peak. Apply with crop oil concentrate or nonionic surfactant.
Stinger: Best suited for spot treatment due to high cost. Effective for Canada thistle and ragweeds, primarily. Apply up to early boot.
A primary goal in management of dense winter annual stands is to control them early enough in spring so that 1) they do not interfere with seedbed preparation or crop establishment, and 2) they do not go to seed and increase in population next fall (chickweed is already flowering and producing seeds). OSU research shows a number of herbicide programs are effective in the fall for winter annual control, and the speed of plant death is not a critical factor in fall applications. However, for herbicide applications at this time of the year, dense winter annual stands may require use of relatively fast-acting herbicides so that plants die and dry out well ahead of planting.
The cool temperatures in March and early April often result in slow herbicide activity, compared to application later in spring when temperatures can be considerably higher. The rate of activity of glyphosate in winter annual plants can be extremely variable at this time of the year, depending upon environmental conditions and plant size and growth stage. While glyphosate can control chickweed rapidly under favorable conditions, control can also be slow enough to prevent the chickweed from interfering with crop establishment. Purple deadnettle appears to be even more tolerant of glyphosate than chickweed.
In OSU research trials, treatments containing Sencor (metribuzin) were among the most rapid of the spring-applied herbicides. Combining Sencor with Gramoxone Max can result in even more rapid control. Products containing metribuzin include Sencor, Domain, Axiom, and Boundary. We suggest using products/rates that provide the equivalent of at least 6 oz per acre of Sencor (at least 8 oz in dense stands), and applying with crop oil concentrate and 2,4-D ester. These treatments will most likely provide the most complete control when applied in higher spray volumes - 20 GPA is likely to be a more effective volume than 10 GPA. The Canopy XL/Express treatment also controlled winter annuals fairly rapidly in the spring, but Express must be applied at least 45 days before soybean planting. Canopy XL will not control chickweed unless it is mixed with a herbicide that has activity on chickweed, which is a primary reason for tank-mixtures with Express. Valor will help control winter annuals in spring also, but has been somewhat variable in OSU research unless mixed with glyphosate and 2,4-D ester.
In corn, atrazine plus 2,4-D and crop oil concentrate was effective on chickweed and deadnettle when applied in early spring in OSU research trials. The addition of other products did not appear to be necessary for control of these weeds. For late-spring applications when chickweed is large and rapid activity is essential, consider a mixture of Gramoxone Max plus atrazine plus crop oil concentrate. Be cautious of 2,4-D ester application around the time of corn planting, since it can injure corn if applied to close to planting with significant rainfall events soon after application.
The early emerging weeds have been spotted. In central Ohio and to the south weeds such as giant ragweed, Atriplex, common lambsquarters, Canada thistle, quackgrass, and probably Pennsylvania smartweed have been observed emerging already. This seems earlier than normal, but we have had enough warm temperatures for emergence to begin. Be sure to scout fields before herbicide applications, so that the appropriate herbicides have been chosen to control the weeds that are presently in the field.
Preplant applications of nitrogen have begun in Ohio. The Ohio State University recommends the following equation for nitrogen recommendations:
N (lb/A) = 110 + [1.36 x (yield potential)-100] - N credit
Credits include previous crops and manure applications. If the previous crop was soybeans, a credit of 30 pounds may be taken. A complete list of credits may be found in the Extension Bulletin E-2567: "Tri-state Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa" or at http://ohioline.osu.edu/e2567/index.html.
Good management decisions with preplant nitrogen may improve the efficiency of the overall program, such as placement method and fertilizer selection. The challenge is to minimize losses, since the corn crop does not need large amounts of nitrogen until the end of May and first part of June. For preplant nitrogen, it is always best to incorporate the material. Anhydrous ammonia is often the product of choice for preplant because of its cost advantage and it takes the longest time to convert to nitrate-nitrogen. Once nitrogen is in the nitrate form, it has the greatest chance to be lost.
This loss occurs because the nitrate form has a negative charge and cannot be held by the soil, which also has an overall negative charge. Thus under the right conditions nitrate-nitrogen can be lost via water movement (leaching, tiles) or converted to nitrogen gas (denitrification). Urea-ammonium nitrate solutions (28-32% nitrogen) may also be used. Incorporation will diminish volatilization losses from the urea component, but the nitrate portion will be susceptible to losses under the right conditions. Of the dry materials, urea has the highest percent nitrogen (46%). Urea volatilization losses may be minimized if incorporated shortly after surface application. Minimum benefit should be obtained from a urease inhibitor if the urea is incorporated into the soil.
A nitrification inhibitor (N-Serve) should be used with anhydrous ammonia on soils that tend to be wet for applications prior to April 15. On well-drained soils, applications at this time probably do not need a nitrification inhibitor. However, the inhibitor would be an advantage in very wet years and diminish the potential of N loss via drain tiles on these soils for very early spring applications. It is an economic decision to be made by the producer (can I justify the cost of the insurance?).
In summary, preplant nitrogen applications have been one method of providing nitrogen for corn production. The nitrogen recommendations for The Ohio State University have been based on studies using preplant applications. Nitrogen rates should be reduced with proper credits for previous crops and manure. Potential nitrogen losses should be diminished with proper placement and selection of nitrogen fertilizer.
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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/
C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
Specialists: Dennis Mills (Plant Pathology), Anne Dorrance (Plant Pathology), Pat Lipps (Plant Pathology), Peter Thomison (Corn Specialist), Ed Lentz (District Agronomist), Jeff Stachler (Weed Science), Mark Loux (Weed Science), Bruce Eisley (Entomology) and Ron Hammond (Entomology). Extension Agents: Barry Ward (Champaign), Woody Joslin (Shelby), Greg La Barge (Fulton), Gary Wilson (Hancock), Mark Koenig (Sandusky), Alan Sundermeier (Henry/Wood), Howard Siegrist (Licking/Fairfield) and Dave Jones (Allen).Editor: Greg La Barge Web Editor: Tom Rosati
Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
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