CORN
Crop Observation and Recommendation Network

March 31 - April 7, 2003
C.O.R.N. 2003-7

In This Issue:

A) Wheat Condition and Management Decisions
B) Nitrogen Consideration for Corn
C) Spring Has Sprung, The Weeds are Back!!
D) 2003 Spring Forces Change in Forage Weed Control
E) The Key to Winter Annual Weed Management - Stopping Seed Production
F) Slug Management

A) Wheat Condition and Management Decisions - P. Lipps and D. Mills CORN Questions

A number of relatively warm days during the last two weeks of March have helped the wheat crop green up after a long and cold winter. Snow cover was relatively consistent from mid-December through the first of March in most areas. The snow cover provided considerable protection to the wheat during the abnormally cold winter months. The accumulated snow began to melt during two warm periods that lasted several days each in early March. The thaw caused significant ponding of snow melt water, which froze during cold periods between thaw events. This caused ice sheeting over many fields but warmer periods in mid March caused the ground to thaw and promoted fields to drain relatively rapidly. Wheat producers can see some damage to wheat in areas where water was ponded or frozen for periods of time. Assessment of wheat stands can be made now as the wheat begins to green up. We are hopefully past the time when freezing and thawing will cause heaving of wheat crowns out of the ground.

Wheat growers should walk into fields to examine plants. Dig plants from areas previously covered with ice or water and examine the crowns by peeling the leaf sheaths back to expose the inner tissues. The inner crown should be creamy white if plants are still alive; any brown discoloration will indicate winter damage and possible death of the plants. Plants that have been heaved out of the ground can be seen at this time as well. These plants may have a few roots attached into the ground, but the crown is completely exposed above the ground. These heaved plants will begin to green up, but as the temperatures rise and soil begins to dry, they will eventually die. Farmers frequently see this initial green up followed by dying of plants and refer to this as the field is 'going backwards'. Soon after green up plants will begin to develop new crown roots from the base of each tiller in the plant. The development of these new crown roots is a sure sign of spring regrowth

Ohio's wheat crop needs to begin regrowth as soon as possible to maintain yield potential. This is because the time for additional tiller development is limited. Warmer temperatures and day lengths approaching 14 hours will stop tiller production (about the middle of April in central Ohio). This is evident as plants begin the stem elongation growth phase (Feekes' growth stage 6). Yield potential is reduced if tiller numbers after green up fall below 25 tillers per square foot. Fifteen tillers per square foot are considered minimal for an economic crop. The number of tillers per square foot is equal to the number of tillers in 20.5 inches of 7-inch wide rows or 14.5 inches of 10-inch wide rows. Damage is more likely to be due to the loss of all plants in areas where ice sheeting has occurred than the loss of a few tillers within rows. The decision is most likely to be whether to keep sections of fields where winter damage has occurred.

Feekes' growth stage 6 or beginning stem elongation is determined when the first node is detected at the base of the larger tillers in the field. You can assess growth stage by pulling tillers from the field and stripping the lower leaves and leave sheaths down to expose the lower stem. The first node should be visible as a hard swelling on the stem at about one half inch to one and one half inch above the roots. This is an important growth stage to know because all nitrogen should be applied by this time and certain herbicides cannot be applied after this time (consult labels to determine proper application timing). . If the weather remains mild during early April, growth stage 6 will likely occur by mid April in southern Ohio and during the following week in northern Ohio.

B) Nitrogen Consideration for Corn - Lentz CORN Questions

The increase cost of N fertilizer this year has many producers re-evaluating N rates for corn. A review of the nitrogen rates, yield goals, nitrogen credits and nitrogen losses may assist in this decision.

For the past several years the OSU Agronomic Crops Team has had meetings and workshops on N management across the state. Many producers were surprised that they were applying 30 to 50 more pounds of N than those recommended by the Tri-States. Some were not aware of the university research and others applied more to be safe. For those who applied more to be safe, they were adding insurance on insurance since the Tri-State recommendations already include a hedge for unusual years of N loss. Producers who have followed these recommendations have not reported yield losses from inadequate N since these recommendations were released in 1995. For producers not familiar with recommendations, they should obtain Extension Bulletin E-2567: Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa. The N equation used for these recommendations is given below:

110 + [1.36 x (yield potential - 100)] - N credit

For example, corn following corn would require approximately 190 lb N/A for a yield potential of 160 bushels. A potential of 140 bu/A would require about 160 pounds of N. As seen in the equation, the value given for yield potential would greatly affect the N recommendation.

Fine tuning the yield goal will have a great affect on the final N rate. Many ways may be used to estimate yield potential, but a conservative method would be prudent in years of high fertilizer prices. Some methods determine the yield average of a field for the past five years or another method may throw out the high and low yielding years of the past five years and average the remaining three. Regardless of the method, a realistic yield goal should be the desired outcome.

Nitrogen credits also need to be considered as well as yield potential to determine N rate. Previous crops, especially legumes, will have N available for the following corn crop. Thirty pounds of N should be deducted from the total N rate if the previous crop was soybeans regardless of the yield from the previous soybean crop. More N may be available in some years, but that increase is difficult to predict in all situations. Nitrogen credits should also be taken if the previous crop was a grass pasture (40 lb), a legume cover crop (30 lb) or alfalfa (60 - 140 lb, depending on the stand density). Many producers neglect these credits, but a producer planting corn after soybeans with a yield potential of 160 bu/A would lower their N needs from 190 to 160 lb/A.

Nitrogen credits should also be given for manure applications. The amount of N available from manure depends on the source, time of application, and application method. Fields regularly applied with manure may not need additional N. In these situations, a presidedress nitrate test (PSNT) should be used to confirm if adequate N levels exist for this year's corn crop.

Management practices affect nitrogen loss potential. Producers control the N source selected, time of application, and placement method. In general, the potential for N loss may be reduced by the following practices: 1) select a N source that remains in the ammonium form the longest period of time, 2) apply most of the N around growth stage V6, and 3) incorporate rather than leave N on the soil surface.

In summary, N prices are higher than usual this year. However, a producer may reduce N costs by following university recommendations, choosing realistic yield goals, claiming N credits, and observing good management practices.

C) Spring Has Sprung, The Weeds are Back!! - Stachler CORN Questions

Based upon observations in Franklin and Madison Counties, summer annual species, spring-germinating winter annual species, and a perennial species have begun to grow! The spring-germinating winter annual species emerging now include marestail/horseweed and prickly lettuce. Numerous summer annual species are beginning to emerge, including giant and common ragweed, common lambsquarters, Atriplex, Pennsylvania smartweed, ladysthumb, wild buckwheat, prostrate knotweed, and wild mustard. In Columbus, we have even seen a few velvetleaf plants emerging, which is very early for this species. As for perennial broadleaf species, Canada thistle has begun to emerge and some plants are upwards of 1.5 inches tall.

The importance of this information is that 2,4-D, glyphosate, or Gramoxone Max should now be added to most residual herbicides being applied to no-till fields in order to control those plants that have emerged.

D) 2003 Spring Forces Change in Forage Weed Control - Loux CORN Questions

Weather conditions in late winter were generally unsuitable for the application of Sencor or Velpar when alfafa was dormant, which is usually a very effective treatment for winter annuals and dandelions. It is now too late for application of these herbicides, since alfalfa is no longer dormant. It is still possible to control winter annual weeds and early-emerging summer annuals with several other herbicides, including Pursuit, Raptor, 2,4-DB, and Buctril. For winter annual control, these should generally be applied as early as possible in spring when winter annuals are small in order to maximize control and forage quality. However, applications should not be made during periods of cold weather, and especially when nighttime temperatures are less than 40 degrees. For more information on these products, see pages 110-123 of the 2003 OSU Weed Control Guide and product labels.

E) The Key to Winter Annual Weed Management - Stopping Seed Production - Loux CORN Questions

Winter annual weeds have become extremely problematic over the past five years, due in part to current weed management strategies that fail to prevent seed production in the spring. Specifically, a failure to either till fields or apply herbicides early enough in spring to control winter annuals and eliminate seed production appears to result in increased populations the following fall and spring. The seed of winter annual weeds often lacks dormancy and is ready to germinate anytime over the next year that soil conditions are suitable. So - the seed from this spring's crop of winter annuals will result in increased populations in the coming fall. Many producers are attempting to control weeds in no-till Roundup Ready soybeans with one postemergence application of glyphosate, or a delayed glyphosate burndown followed by a postemergence glyphosate application. This type of herbicide program appears to result in an increase in dandelions, marestail, and winter annuals in some fields. In fields that did not receive a herbicide application to control winter weeds last fall, we strongly suggest: 1) application of herbicides early enough in spring to prevent winter weeds from interfering with crop establishment and to eliminate seed production; and 2) including herbicides with residual activity to control seedling dandelions and marestail and help manage tough summer annual weeds such as giant ragweed, morningglory, and lambsquarters.

F) Slug Management - Hammond and Eisley CORN Questions

Slug population densities were heavy in many Ohio fields in 2002, and along with the late planting, farmers experienced some of the worst problems they have ever faced. Sampling in the fall of 2002 revealed high slug populations, and recent sampling this past week has indicated fields with a lot of eggs. These numbers suggest that spring slug populations might again be high. Corn and soybean growers who have had problems with slugs in the pasts should monitor their fields very closely for slug populations and injury. Growers should realize that tillage continues to be an option for management of slugs in both corn and soybean fields. Tillage lowers the potential for damage because it removes the residue that provides a favorable slug habitat. However, the use of tillage should be weighed against the benefits of no-tillage production practices.

Because slug damage often occurs at germination and crop emergence resulting in significant stand loss, especially in soybeans, growers with high slug populations and a history of poor soybean stands due to slugs might want to consider an at-planting time application of molluscicide bait. Growers should determine if slugs are present and active at the time of soybean planting in order to make the appropriate decision. This is best done by searching at the soil level underneath the crop residue for the presence of slugs and/or slug eggs. If mainly eggs are seen, growers should plant and watch their crops closely. If slugs have hatched and are growing and active, treatment might be warranted. Stand problems usually are more of a concern with later planted crops; those planted in later May and early June.
When treating, the most common molluscicide is Deadline MPs, which should be broadcast at 10 lbs per acre. If past history suggests that only certain areas of a field have had a problem, only those areas need to be treated. There is also a new molluscicide that should be available this spring, Sluggo. This bait contains iron phosphate rather than metaldehyde. Studies suggest that iron phosphate baits should be applied at higher rates to get acceptable control, perhaps 15-20 lbs per acre. As always, check areas, approximately 100 by 100 ft, should be left to determine the treatment's efficacy.

Because of the continued problems with slugs in no-till, persons from the OARDC, OSUE, SWCD, NRCS, and ODNR-Soil & Water Conservation have met to address grower concerns. Numerous on-field trials are being planned to examine alternative methods of management, including the use of rotary harrows and Aerways. We are also planning on conducting soil testing to determine if differences in soil chemistry, especially soil pH, might affect slug populations and injury.

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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.

Editor: Greg LaBarge        Web Editor: Nathan Watermeier

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