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July 3 - July 9, 2000
C.O.R.N. 2000-20
In This Issue:
A. Planting Soybeans In July For Northwest Ohio
B. Leafhopper Activity Increasing On Alfalfa
C. Weed Control In Double-Crop Soybeans
D. More On Effects Of Ponding And Saturated Soils On Corn Growth
E. Key Steps In Corn Pollination
F. Options For Supplemental Emergency Forage
Fields have still been too wet for some growers to plant
soybeans, or patch in previous lost stands. Success at this time depends upon
late July and August rainfall. Two years ago, adequate August rains allowed
some growers to get 40 bushels from late plantings. However, last year was more
typical were yields were minimal from dry conditions.
Maturity selection is important for late-planted soybeans to maximize growth
before flowering for larger yields. This concept is shown in one of my research
plots at the Northwestern Branch of O.A.R.D.C. in 1999, where a June 25 planting
gave the following yields for the corresponding maturity group: 2.1, 11.9 bu/A;
2.5, 12.5 bu/A; 3.0, 17 bu/A; and 3.5, 16.3 bu/A. Some limitations of the study
were only one variety was used for each maturity group and populations were
not increased for the late planting date. Also, the extended fall allowed all
groups to mature. If you plan to plant soybeans this week in Northwest Ohio,
consider the following management tips: Seeding rate of at least 250,000 plants
per acre
Throughout late May and early June, PLH activity remained relatively low, signs of nymph activity were minimal, and alfalfa growth was optimal under conditions of period rainfall. However, during the past two weeks, conditions have become dryer, PLH adult activity began to increase, and nymphs have become abundant. Although second cutting alfalfa probably did not need treatment for PLH, treatment of third cutting alfalfa for PLH may very likely be warranted.
Where PLH activity exceeds the treatment threshold (when the number of PLH per ten sweeps is greater than the height of the stand expressed in inches), the optimal time for treatment is when the stand height is about six to eight inches and nymphs are just beginning to appear. The most effective method for evaluating PLH activity continues to be the use of a sweep net. Use of a cap in place of a sweep net, making pant leg observations, or waiting to see some hopper burn on the foliage are not valid methods for assessment of potential PLH impact.
A number of products are available for treatment of PLH
on alfalfa such as Baythroid, Warrior, Pounce, Ambush, Lorsban, various formulations
of dimethoate, etc. Most products labeled for PLH on alfalfa will provide effective
control if applied in a timely manner. In field trials, the newer third generation
synthetic pyrethroid products (Baythroid 2E and Warrior T) generally provide
optimal control of PLH, even when applied at reduced rates.
Double-crop soybeans should require less herbicide compared to full-season soybeans, since weed emergence is much reduced in mid-summer. However, there may be emerged weeds lurking under the wheat stubble that will start to grow in response to their exposure to sunlight. In addition, there can be emergence of additional grass and broadleaf weeds. Past research has shown that control of weeds at the time of double-crop soybean planting accounts for up to 75% of the weed control needed. An application of glyphosate or paraquat prior to soybean emergence is thus essential in non Roundup Ready soybeans.
When applying postemergence herbicides to double-crop soybeans, try to avoid excessive soybean injury that will slow plant development. When soybeans are planted late in the season, there is more possibility for yield reduction due to herbicide injury. Late-planted soybeans have less time to recover from injury before the reproductive process begins, and the severity of injury is more of a concern than in early-planted soybeans. Research at Penn State in 1989, 1991, and 1993 indicated there may be some need to stay away from certain postemergence herbicides in double-crop soybeans. In the Penn State study, postemergence applications of Pinnacle were applied in early August, and resulted in 15 to 37% soybean injury. Yield was significantly reduced (4 to 15 bu/A) from this degree of injury. There was no yield reduction or injury where Pinnacle was applied to STS soybean cultivars.
Roundup Ready soybeans can have a good fit in double-crop fields, since applications of glyphosate do not slow soybean growth or development. One application of glyphosate within a few weeks of planting should be sufficient weed control, avoiding the need for a herbicide application at the time of planting. The technology fee associated with Roundup Ready soybeans does increase up-front investment. This may deter use of this system, since return from double-crop soybeans is extremely variable. However, if the use of Roundup Ready soybeans eliminates the need for one herbicide application, cost estimates may actually favor the Roundup Ready system. A very rough cost breakdown (not including application costs):
Conventional soybeans - 1 quart/A glyphosate at planting ($10/A) followed by postemergence grass/broadleaf herbicides ($20/A ?) = approx $30/A
Roundup Ready soybeans - Technology fee ($10/A ?) + 1 qt/A postemergence glyphosate application ($10) = approx $20/A
Saturated soil conditions continue to cause problems in many corn fields, especially in NW Ohio. The good news is that much of this corn is at vegetative stage of development (beyond V6) which is more resistant to injury caused by anaerobic soil conditions. However, variable soil moisture/drainage conditions have resulted in uneven growth and development across fields. In addition, denitrification associated with protracted periods of saturated soil conditions may result in nitrogen deficiencies and reduced yield potential later in the growing season. The following is adapted from an article by Dr. Bob Nielsen at Purdue University that addresses the impact of these soggy soil conditions on crop performance.
Soggy Soils Severely Stunt Stands of Corn
Is the drought over for this year? According to both the National Drought Mitigation Center and the Climate Prediction Center (NOAA), Indiana is drought-free for the first time in this millennium. Certainly the recent rains across the state have helped us forget about drought stress for the time being. In fact, quite a number of corn fields are instead suffering from the effects of soggy soils on root health.
An earlier article shared my thoughts on the effects of flooding and ponding on corn survival. After walking a number of fields since then, it seemed appropriate to share some additional observations on the effects of soggy soils on crop health. The consequences of ponding or saturated soils on corn health can be astounding in late June when temperatures are in the 80's. In fact, some folks call and ask how can corn be so dramatically stunted in so short a period of time?
First of all, some areas have been soggy off and on for weeks now. The saturated soil condition didn't just happen overnight. The accumulated stress of chronic 'wet feet' takes a greater toll on root health than does a single soggy event.
Secondly, not only are we seeing the effects of nitrogen loss (denitrification or leaching) on overall corn appearance in the soggy areas, but the plants' roots are also literally dying from the lack of soil oxygen. These two factors together are very damaging to the health of a corn crop. Consequently, one will often find a blurred mixture of true nitrogen deficiency and plain old leaf death from dying roots among plants in soggy areas.
Thirdly, the effects of soggy soils are protracted in poorly drained no-tilled fields with significant levels of surface trash. Surface trash limits soil evaporation and extends the time period within which the soils remain saturated. Corn health can deteriorate amazingly fast under such conditions.
Fourthly, some hybrids simply have a lower tolerance to 'wet feet' than others. Unfortunately, few, if any, companies rate their hybrids for such tolerance. Even they did, Murphy's Law says that hybrids tolerant to soggy soils would probably be susceptible to drought conditions!
Finally, another factor related to the apparent rapid deterioration of corn in soggy areas is that the corn growing outside of those areas continues to grow normally. In fact, given the warm temperatures of late plus the ample supply of soil moisture plus the fact that the crop is smack dab in the middle of its rapid growth phase all contribute to a rapid rate of crop growth and development. So, part of our astonishment at the severity of stunting in the soggy areas is an optical illusion of sorts caused by the fact that the rest of the field is growing by leaps and bounds. Consequently, the appearance of the stunted yellowish corn in the soggy areas is amplified by the rapidly developing taller dark green corn in the drier areas of the field.
Management Decisions: The primary management decision to be considered as a result of soggy soils in corn fields is whether those areas will benefit from any additional nitrogen fertilizer applications once the soil dries enough to support ground equipment. Loss of available soil nitrate is in the neighborhood of five percent per day of waterlogged soils and consequently will constitute significant N loss in areas of some fields this year. The complicating factor for many Indiana corn fields from here on is that they are already beyond the maximum safe height for traditional sidedressing equipment. Even if the stunted areas are technically short enough for ground equipment, the height of the healthier areas of the fields will prevent traditional ground equipment from getting to the stunted areas without causing significant damage on the way.
The following advice on how to apply late N fertilizer comes from John Sawyer at Iowa State University (http://www.ent.iastate.edu/ipm/icm/2000/7-3-2000/whataboutn.html) : "When conventional application equipment can be moved through the field (the soils are dry enough and the corn is short enough), then injection of anhydrous ammonia or UAN solutions would top the list of best options. Next would come dribble UAN between corn rows, then broadcast urea. Broadcast UAN solution should be avoided because it can burn corn foliage, especially with large corn. If injection or conventional broadcast application is not possible ..., then UAN could be applied with high-clearance equipment with drop nozzles that direct the solution onto the ground, or urea could be aerially applied."
The other complicating factor is the extent of 'permanent' stunting of the crop caused by the soggy soils themselves. A 50 percent loss in soil N is not very important if 50 percent of the crop's yield potential is already lost simply due to the soggy soils. From a number of fields that I have seen recently, the stunting is so severe that I doubt that additional N will pay for itself.
Finally, be prepared for variable grain moistures at harvest. Remember that the stunted corn in the soggy areas is not simply short but is also stunted in its development. If the plants survive, pollination will occur later than in the rest of the field. Consequently, any grain that is produced in these later pollinating areas of the field will also mature later and will be wetter at harvest than that from undamaged areas of the field.
Bottom Line: Many Indiana corn growers will tell you that they don't mind the drowned out areas of their fields because that usually means there has been sufficient rainfall for the rest of their fields to yield very well.
The flowering stage in corn is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Drought, high temperature stress, as well as hail damage and insect feeding have the greatest impact on yield potential during the reproductive stage. The following is an overview of key steps and phases in the corn pollination process.
Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. On a typical midsummer day, the shedding of pollen is in the morning between 9:00 and 11:00 a.m.
The tassel is usually fully emerged and "stretched out" before any pollen is shed. Pollen shed begins at the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen.
Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.
Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rain storm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs which serve to catch and anchor pollen grains
Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours.
A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.
Pollen of a given plant rarely fertilizes the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant are pollinated by other plants in the field.
The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought. Poor seed set is more often associated with poor timing of pollen shed with silk emergence (silks emerging after pollen shed).
Many Ohio livestock producers are faced with a need for supplemental forage because of wet soil conditions. In some areas, the wet soils have prevented row crop planting, which now provides an opportunity for forage production. Our options for planting supplemental forage now are limited primarily to the summer annual grasses. Below is a brief description of these forage species to consider. Refer to the Ohio Agronomy Guide (http://ohioline.ag.ohio-state.edu/b472/forage.html) for more information on establishment and management of these crops. Feeding these forages should be based on forage quality analyses and ration balancing to meet the herd's nutritional and energy requirements.
Summer-annual grasses include sudangrass, sorghum x sudangrass hybrids, pearl millet and other millet species, and forage sorghum. These grasses grow rapidly, and when managed properly can provide forage of good quality. Summer-annual grasses are a good double-crop option when planted after a small grain crop. All these species can be planted up to July 15, and will produce a good crop assuming sufficient moisture is present for emergence and growth in the later half of the summer. Pearl millet is essentially free of prussic acid poisoning potential, and the sorghum species vary in degree of prussic acid poisoning potential. Nitrate toxicity is possible with all summer annual grasses. Refer to the Agronomy Guide for how to reduce these risks and for management guidelines. Brown midrib forage sorghum and sorghum sudangrass are now available, and provide an excellent option. These varieties contain less lignin and are more digestible and more palatable than standard varieties. In addition, yield reports do not show any forage yield drag associated with the brown midrib trait in sorghums. Brown midrib sorghum grasses will, however, still contain the same prussic acid poisoning potential as standard varieties. At the end of this article are listed seed sources for brown midrib sorghums that I know of in Ohio and Indiana. Others may exist, so ask your local seed supplier.
Mixtures of summer-annual grasses and legumes such as field peas and soybeans are being marketed by some seed dealers. The legumes generally improve protein content compared with summer-annual grasses grown alone. Field peas may not do well when planted this late, because of the hot weather. If soybeans are included in the mix, Group V or VI varieties will probably produce better forage yields when planted this late in the season.
Soybean can be grown alone for forage, but use of herbicide-treated soybeans for forage or hay is allowed for only a few herbicides, so check the label before using herbicides on soybeans to be used for forage. Harvest soybeans for hay to optimize yield and quality when seeds are filling the pods and the lower leaves of the plant are just beginning to turn yellow. If harvested for silage at this stage, soybeans should be mixed with corn in the silo to achieve acceptable fermentation. Mix one part soybean with two or more parts of corn in the silo. Soybean forage should comprise no more than 30 to 40% of the dry matter intake of the animal, because of its high oil content (assuming it was harvested when seeds were formed). This level will not be exceeded when soybean and corn silage are ensiled together in the proportions described above.
Small grains such as rye and wheat can be planted in late August for late fall forage (especially when grazed) and then kept over winter for forage next spring. Oats planted with wheat or rye can increase fall forage yield, but may cause small decreases in forage yield of wheat and rye next spring. Brassica crops such as turnip and rape are fast-growing crops that are good options for grazing, especially for sheep and beef cattle. These crops are highly productive, and can be grazed from 80 to 90 days after seeding. These crops must be treated more like "concentrates" than "forage" in nutritional planning for livestock because of their high digestibility and low fiber content. They are seldom used as dairy feed because they can cause an off-flavor in milk. Additional information is provided in the Ohio Agronomy Guide.
Seed Suppliers of Brown Midrib Forage Sorghum and Sorghum Sudangrass: (other suppliers may exist, so ask at your local sources of forage seeds)
Ag Nation Products
East Canton, OH 800-247-3276
CISCO
Indianapolis, IN 800-888-2986
Grazing Systems Supply & Griewe Seed
Greensburg, IN 888-635-8588
TenBarge Seed, Inc.
Haubstadt, IN 800-467-0158
Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.
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.
Contributors to C.O.R.N. this week include: State Specialists: Peter Thomison (Corn Production), Hal Willson (Entomology), Ron Hammond (Entomology), Mark Loux (Weed Science), Jeff Stachler (Weed Science), and Mark Sulc (Forage Production); District Specialists: Ed Lentz (Agronomy); Extension Agents: Dave Jones (Allen), Steve Bartels (Butler), Barry Ward (Champaign), Howard Siegrist (Licking), Glen Arnold (Putnam), Ray Wells (Ross), Clark Hutson (Seneca), and Roger Bender (Shelby).
Editor: David A. Jones 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.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
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