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For Month of February, 1998
C.O.R.N. 98-2
In This Issue:
A) Nitrogen Management for the 1998 Wheat Crop
B) Phytophthora Resistant Soybean Varieties
C) Soybean Seed Treatments
D) Rhizobium Inoculants and Seed Treatments
E) Performance Information on Specialty Corns
F) Mild Winter and Insect Populations
G) Choosing Corn Hybrids for Silage
By the end of January, Ohio's winter wheat crop had been exposed to sufficient cold weather to be vernalized so that it will head and produce grain. As of February 20, 1998 most wheat in Ohio had broken dormancy and was actively growing whenever temperatures were above 40 degrees F. The absence of extremely cold temperatures and dry air during the winter months allowed most of the leaf tissue to remain green and capable of fixing sunlight whenever temperatures were satisfactory and the sun was shining. This abnormal weather provides for potential windfalls and pitfalls depending on the kind of weather the crop experiences between late February and mid April.
If the abnormal warm weather continues into spring, then wheat will likely head earlier than normal. If it is not killed by high temperatures earlier than normal in late June and there are no other major problems, yields for many fields could surpass 125 bu/ac. Each additional day of grain filling above the normal 20 days can add 3 to 4 bushels of yield. Severe disease problems can limit these potential yield increases to less than a bushel per acre per day. The potential for earlier-than-normal lush growth increases the potential for disease and fungicide applications may be needed earlier in the year than is customary.
The down side potential for this year's crop is that a hard freeze could occur after jointing when the growing points are above ground and kill the plants, or less severe temperatures could damage very lush leaf tissue thus reducing photosynthesis and providing increased potential for leaf disease.
The normal recommendation for nitrogen application is to apply one pound of nitrogen for each bushel of yield goal between early March and mid April. Because of the advanced development of the crop, it may be prudent to delay N application until early April as a means to limit potential damage due to a hard freeze. A split application with 75% of the nitrogen in the second application would also be a hedge against freezing damage. All formulations of dry nitrogen material are satisfactory for either one-timeor split applications. Liquids should be applied with dribble bars or very coarse flood nozzles that apply very large droplets or in a way that minimizes the amount of leaf coverage. Application a few hours before rain will reduce leaf damage as will dilution of the nitrogen to a 14% solution. Once on the soil surface, nitrogen moves very freely and can diffuse up to a foot in a few hours if the soil is moist. Therefore, uniform application within an area two feet by two feet is much less critical than the rate of application.
As of late February, wheat was dark green in color. Because there is little available nitrogen in the soil, root systems are small and soil temperatures are low, much of this green color will be lost in early March. The impact will be more cosmetic problem than a yield reducing problem. An application of a small amount of nitrogen will help reduce that nitrogen deficiency. The dark green color will be recovered very slowly due to cold soil temperatures. The most important management practice is to have adequate nitrogen available in April and May when the demand is greatest.
Farmers should not underestimate the need for growing Phytophthora resistant and or partially resistant (tolerant) soybean varieties in Ohio. Yield increases from growing resistant soybean varieties has been as high as 15-30% or more in fields where the disease has occurred. Our long term data indicates that nearly a third of the fields in Ohio will have damage from Phytophthora nearly each year. The risk of damage from Phytophthora increases with reduced tillage, especially on poorly drained soil. Farmers are encouraged to plant soybean varieties with race-specific resistance or partial resistance. Varieties with race specific resistance to most of the current Phytophthora races are available from various seed companies.
Race specific resistance is conditioned in soybean varieties by the presence of single genes or Rps genes. Currently, the most effective genes in Ohio are Rps 1-c, Rps 1-k, and Rps 3-a, or combinations of these genes. These genes only protect against certain races of the fungus and provide a high degree of protection in varieties that carry the resistance genes to these races. However, the resistance is totally ineffective against other races that may be present in fields. Varieties with partial resistance (also called tolerance) have a lower level of resistance, but the resistance is effective against all races. Soybean varieties can have both types of resistance. It is highly recommended to use varieties with race specific resistance and an effective level of partial resistance in fields with a history of Phytophthora. Thus, if a race occurs in a field that can attack the Rps gene, the partial resistance will prevent high stand loss and yield loss. Some of the new Roundup Ready soybeans have Rps resistance genes, but very low levels of partial resistance. There is a possibility that these varieties may be attacked by certain races of Phytophthora in the field and without a certain level of partial resistance, stand losses could occur. Talk to your seedsman about the Rps genes in the variety and ask about the level of partial resistance (tolerance). Information on some of the Roundup Ready soybean varieties can be found in the OSUE Soybean Performance Trial available from OSU Extension offices in each county.
Soybean seedlings are vulneralbe to a number of seed- and soil-borne diseases. None of the specific seed treatment fungicides alone will control all of these diseases. Effective control depends on the type of fungicide and the rate of active ingredient in the seed treatment product. Because of the number of different diseases affecting soybean seed and seedlings, seed treatment products are usually made up of several different fungicides that act against more than one pathogen. Phomopsis seed rot affects the germination of seed. Seed treatment fungicides like captan, thiram or TBZ are effective in increasing germination of seed affected by Phomopsis. Rhizoctonia seed and stem rot is difficult to control even with the best seed treatment fungicides. Currently, the only labeled materials effective against Rhizoctonia are carboxin (Vitavax) and PCNB. Pythium and Phytophthora reside in the soil and attack seed and seedlings when the soil becomes satruated. Captan and thiram have activity against seed rot caused by Pythium, but neither has activity against Phytophthora. Apron is effective in controlling both Pythium and Phytophthora.
In Ohio, it is essential that soybeans be treated with Apron to control Phytophthora damping off in areas with a history of stand losses due to this disease. Apron is recommended for use on varieties with single generesistance (RPS genes) and those with partial resistance (tolerance) toPhytophthora. The Apron treatment will also protect against Pythium seedrot and damping off. Apron FL, at 0.2 fo. oz./cwt and Apron XL at 0.16 fl.oz./cwt, will control Pythium seed rot and damping off. However, higher rates are needed to achieve good control of Phytophthora. For Phytophthorause 1.5 fl. oz/cwt of Apron FL or 0.64 fl. oz./cwt of Apron XL. Farmers should be aware that most seed companies are applying Apron at a rate lower than needed for good Phytophthora control. If you have lost stands to Phytophthora in the past, ask your seedsman what rate of Apron was applied before purchasing the seed. Half rates of Apron cost less and also give less protection from stand loss because low rates may result in failure to control Phytophthora damping off in the field.
Rhizobium and Bradyrhizobium are bacteria which can fix nitrogen from the air or collect nitrogen from the soil water solution and incorporate it into compounds that plants can utilize. The nodules that form on soybean roots are the sites where the bacteria reside. There are Rhizobia present in Ohio soils, but the commercial strains and some newer strains identified by the USDA are much more efficient at fixing nitrogen. The bacteria may be applied to the seed or placed in the seed furrow at planting.
Insecticide and fungicide seed treatments can have a negative impact on inoculants applied to soybean seed. Several factors affect the impact of seed treatments on seed applied inoculants including: toxicity of material, toxicity of carrier or formulation, length of time inoculant is in contact with seed treatment and formulation of inoculant. Insecticide seed treatments tend to be the most toxic of all seed treatments to inoculants. The fungicides themselves are not necessarily the problem, but the formulation or carriers may inhibit Rhizobial growth and colonization. Using fungicides in combination with inoculants can be successful if some precautions are taken. If a specific material is highly toxic to inoculants then placing the inoculant directly in the furrow and not on the seed is recommended. Treating the seed first and allowing the seed treatment material to dry followed by using humus preparation of inoculant may be successful. Liquid inoculants and fungicides should not be mixed and applied simultaneously. Producers should minimize the time the inoculants are in contact with the seed treatment fungicides prior to planting.
Table 1. Response of Inoculants in combination with fungicide seed
treatments.
Fungicide |
Fungicide Formulation |
Inoculant Carrier |
Compatibility |
Comments |
Agrosol T |
WP |
Liquid |
No |
|
Rival |
Liquid |
Liquid |
No |
|
Apron XL |
Liquid |
Liquid |
Yes & No |
Tests after 4 hrs were with low rate |
Specialty corns are receiving greater attention by Ohio corn growers as potentially profitable alternatives to yellow dent corn. There is a diverse group of specialty corn types including food grade corns and popcorn which have commercial utilization.
Hybrid performance trials in most states including Ohio do not routinely evaluate these specialty corns in their testing programs. However, there is a regional testing program coordinated by USDA-ARS and the University of Missouri for white food grade corn. This cooperative testing program involves a number of state universities including Ohio State. As part of this multistate screening program, we conducted a white corn test in Ohio at the OARDC NW Branch at Hoytville in 1996 and plan to continue this effort in 1998. (The1997 test results were not reported because of poor stands caused by excessively saturated soil conditions). Results of the multistate white corn testing program are published yearly and provide comparisons of commercial white corn hybrids. Data presented in the publication include food quality characteristics as well as the typical agronomic traits. Please contact me if you would like to receive a copy of "White Food Corn -1997 Performance Tests, Spec. Rep. 510."
There used to be a multistate popcorn performance program coordinated by Purdue University which compared popcorn hybrids for agronomic and quality traits. However this program was discontinued several years ago.
In 1997 we initiated a program to evaluate TC BLEND seed products used in TOPCROSS high oil corn production. The major objective of these tests was to compare the agronomic performance and grain quality characteristics (i.e. oil content) of TC Blends that are adapted to Ohio growing conditions and commercially available to corn growers. The high oil corn tests were established at the Ohio State University (OSU) - Ohio Agricultural Research and Development Research (OARDC) Western Branch Research Farm near South Charleston (S.Charleston) in southwest Ohio and the OSU- OARDC Northwest Branch Research Farm near Hoytville in northwest Ohio. Twelve high oil TC Blends representing seven different seed companies were planted at each site. Three normal corn hybrids were included in the trials as checks along with a new conventional high oil corn hybrid.
Results of these tests are summarized in a recently published OSU Extension Fact Sheet, "1997 High Oil Corn TC Blend Performance Tests" (AGF-136-98). Another OSU Fact Sheet, "Top Cross High Oil Corn Production: Management Considerations" (AGF-135-97) addresses cultural practices necessary for successful high oil corn production.
The past winter has been warmer than usual. Part of the winter was fairly dry and then the rains began to come day after day. In addition, daffodils and tulips are already beginning to emerge. Given the unusual winter conditions, questions on the effect of such weather on insect pests have been raised. The response to such questions must be rather speculative, but a few points can be emphasized. First, it should be emphasized that the early spring weather generally has a greater effect on the development of pest populations than winter conditions.
Second, it should be noted that a number of key pests like black cutworms and potato leafhopper are southern migrants, which are primarily influenced by the spring weather patterns. If this mild winter leads to an early spring, then we may anticipate problems with the migrants.
One pest problem commonly associated with mild winters is the transmission of Stewart's wilt by flea beetles the following spring. The problem primarily impacts sweet corn, popcorn and seed growers, who will need to maintain a close watch for flea beetle activity in the spring.
For many pests, the mild winter may have an effect of reducing winter survival. A good example is the over wintering larvae of corn borer, which is more susceptible to predators and diseases during a mild winter. Corn borer survival often improves during long winters with a heavy snow pack.
A pest like the bean leaf beetle, which over winters in the adult stage maybe a serious problem following a mild winter. Thus, growers planting early soybeans should closely monitor early emerging fields for excessive levels of defoliation.
Pests like the alfalfa weevil and the cereal leaf beetle, which are normally controlled by beneficial parasites, may or may not be a problem depending on the synchronization of pest and parasite population development.
In summary, insect pest problems on field crops this year could be high or low. Thus, it is important to maintain a close watch of pest development in the spring to detect any unusual activity.
Corn hybrid selection is one of the most important management decisions in silage production. Selecting hybrids for silage production depends on whether a field is planted specifically for silage or whether the field maybe harvested for grain (dual purpose). Many farmers and livestock producers grow corn for both grain and silage and wait until harvest nears to determine which fields to use for each purpose. This approach is justified because at planting it is difficult to predict overall forage needs later in the year or know the condition of the corn crop at harvest.
Recent studies show that forage quality differences can occur among commercial corn hybrids. These differences should be considered when selecting corn hybrids for silage. Because silage yield and quality performance data are not always widely available, consider the guidelines outlined below when selecting silage hybrids.
To select silage or dual purpose silage/grain hybrids: Identify a group of hybrids that are adapted to your area in terms of maturity, standability, disease and insect resistance, and drought tolerance. Consider hybrid maturity. Higher silage yields are generally produced with hybrids that mature slightly later (5 to 10 days) than those adapted for grain production. Other factors such as feed inventory requirements, harvest timing, and the potential for wet soils at harvest may warrant use of early maturing hybrids. Plant several hybrids that differ in maturity to spread the harvest workload and to provide a wider window for harvesting quality forage.
Evaluate the group of adapted hybrids for high grain yield potential, even if you plan to harvest only for silage. Many studies have shown that high grain yielding hybrids will at least be better than average for silage yield. However, within the high grain yielding group there can be significant differences in whole plant yield and quality. Tonnage differences can vary by up to 5 tons per acre among hybrids within the same maturity. If information on silage yield is available, use it.
Finally, after considering agronomic performance, focus on quality. Differences exist among commercial corn hybrids for digestibility, NDFdigestibility and protein. Consult your seed company representative or agronomist for silage quality information. A number of companies are developing forage quality profiles of their corn hybrids.
A dual-purpose grain/silage hybrid should have both high grain and high forage yields. Hybrids grown exclusively for silage should have high forage yields, high digestibility, low fiber levels and stover that is highly digestible. Keep in mind that the best silage hybrids usually have high grain yields because grain is so highly digestible.
Source: Lauer, J. 1997. More mileage from corn silage: selecting hybrids.University of Wisconsin Agronomy Advice - Field Crops 28.5.
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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.
Contributors to C.O.R.N. this week include: Pat Lipps (ExtensionSpecialist, Plant Pathology), Hal Willson (State Extension Specialist, Entomology), Peter Thomison (Extension Agronomist, Corn Production), CurtisYoung (IPM), Mike Estadt (Pickaway Co.), Tom Krill (Van Wert), John Barker (Knox Co.), Greg La Barge (Fulton Co.), Howard Siegrist (Licking Co.),Clark Hutson (Seneca Co.) and Steve Prochaska (Crawford Co.).
Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination 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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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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