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March
11-March 25, 2002
C.O.R.N. 2002-5
In This Issue:
A) Corn
Profit Tips-Planter Maintenance And Stand Establishment
B) Soybean
Growth Habit, Yield And Relative Maturity
C) Wheat Condition
In Ohio
D) Wheat Stand Evaluation
E) Predicting
Flea Beetle Activity & Stewart's Disease On Corn
Uneven plant spacing and emergence can reduce yield potential. Seed should be spaced as uniformly as possible within the row to ensure maximum yields and optimal crop performance regardless of plant population and planting date. Corn plants next to a gap in the row may produce a larger ear or additional ears (if the hybrid has a prolific tendency), compensating to some extent for missing plants. Skips reduce yield in fields where the intended population is at or below the optimum, while doubles increase yield when populations are less than optimum. Reduced plant stands will yield better if plants are spaced uniformly than if there are large gaps in the row. As a general guideline, yields are reduced an additional 5 percent if there are gaps of 4 to 6 feet in the row and an additional 2 percent for gaps of 1 to 3 feet.
Uneven emergence affects crop performance because competition from larger, early-emerging plants decreases the yield from smaller, later-emerging plants. If the delay in emergence is less than two weeks, replanting increases yields less than 5 percent, regardless of the pattern of unevenness. However, if one-half or more of the plants in the stand emerge three weeks late or later, then replanting may increase yields up to 10 percent. Emergence delays of 10 days or more usually translate to growth stage differences of two leaves or more. When two plants differ by two leaves or more, the younger, smaller plant is more likely to be barren or produce nubbin ears. To decide whether to replant in this situation, growers should compare the expected economic return of the increased yield with both their replanting costs and the risk of emergence problems with the replanted stand.
To improve planter
accuracy and enhance uniformity of emergence, consider the following:
Varieties with determinate growth habit (maturity groups V through IX) are grown in the states south of Ohio and are characterized by growing vegetatively early in the season, and then switching into the reproductive mode as does corn which also has a determinate growth habit. Varieties with this growth habit usually grow to a larger size than varieties with an indeterminate growth habit, and therefore perform well in rows spaced up to 30 inches apart. The seed of these varieties is usually very small compared to the varieties adapted to the Midwest.
When varieties are moved northward from their area of adaptation, they flower earlier in the growing season than normal resulting in reduced yield. When varieties are moved southward from their area of adaptation, they flower later in the growing season and grow taller than normal. Most varieties perform best in a zone about 100 miles wide north to south and movement east and west has little effect on performance.
When grown on narrow rows, relative maturity has little effect on productivity. For varieties with relative maturities of 2.3, 2.8, 3.3, 3.8 and 4.3 yields in the Ohio Soybean Performance trials were 49.8, 51.0, 52.0, 51.5 and 50.0 bushels per acre respectively. This data shows the effect of relative maturity on grain yield when grown in rows spaced 12 inches apart. Rows spaced 7 inches apart would reduce the yield difference between maturity groups while wide rows (20" - 30") would increase the difference with lower yield at the early and latest groups. This data comes from the Ohio Soybean Performance Trials from 1990 through 1998 and represents about 20,000 plots.
Wheat is an amazing plant; it seems to survive nearly all the impossible situations that Mother Nature and we present it. Wheat planting was behind schedule last fall and with the heavy rains in October in some areas of Ohio with some of the crop even replanted in late October and November. This was not a good start for the wheat crop in the western and northwestern counties. Wheat in other areas looks fair to good, depending on planting date and winter conditions.
Research results have consistently indicated wheat performs best when planted on the Hessian Fly Safe date, or within the first week afterwards, especially if the seed was planted sufficiently deep (1.5 inches) so that the young plants have time to develop a good root system and at least 3 to 4 main tillers by the time it goes into winter dormancy. Fortunately the mild weather in November and early December provided more time for the crop to grow before it went into dormancy by late December. Most late-planted fields had plants with only one tiller in late December.
The dormancy period for wheat was probably quite short this year. In early February we dug and examined plants to evaluate if they had broken dormancy and if any growth had taken place. Although the wheat crop had not shown any growth, we feel the plants probably broke dormancy sometime during the warm weather that occurred during the last two weeks of January. A cold period followed this January thaw, and then another warm period occurred in mid February. The wheat crop greened up during this mid-February warm spell indicating the plants were using their carbohydrate reserves. The wheat will again use and deplete these food reserves every time the temperatures get warm enough. The plant will make no new carbohydrates until temperatures get high enough to support photosynthesis (perhaps by late March).
In the first week of March there was another cold spell. We are concerned that the wheat crop will continue to look worse until there is a long enough period to provide sufficient warmth to initiate new growth and nutrient uptake. Then beginning of wheat regrowth after winter in Ohio has varies greatly. Over the last 5 years regrowth has resumed from between the last week of February to the first week in April. This "time of regrowth" is entirely dictated by the weather. With the weather conditions we had this year, the earlier regrowth begins the better it will be for our crop.
Varieties differ in their ability to make and store carbohydrates in their tissues and they differ in their response to the duration of warm weather required to break dormancy. In general, varieties with good winter-hardiness store more carbohydrates and they are generally the latter ones to break dormancy in late winter. Also, wheat varieties developed for more southerly states may break dormancy after a short warm period, then when cold resumes, these fields turn yellow or brown.
The first few weeks of March are critical to wheat survival. During this time the wheat is frequently trying to regrow, but cold injury and frost heaving significantly affect the plants ability to grow. With the variable weather we have seen this winter and the severe frost heaving in some fields we suspect many fields will look a lot worse before they begin to show significant growth this spring. Scout fields now to check for frost heaving of plants. Usually frost heaved plants occur on higher ground, especially on soils with high clay content. These areas will look brown in comparison to plants on the lower ground.
Once the crowns are heaved out of the ground they will have difficulty reestablishing roots because the remaining roots become desiccated (dried out) during the day. Additionally, since the growing points are above the soil surface, they are vulnerable to cold injury. Frequently, frost heaved plants die or produce few weakened tillers. Help avoid heaving by placing seed deeper during planting and by planting earlier. No-till planting frequently reduces heaving problems especially if seed are placed below, and not in, the surface residue.
Applying nitrogen now before the plants are actively growing may only cause additional problems by stimulating succulent tissues susceptible to cold injury. Assuming 20-30 lb of N was applied in the fall at planting, these overwintered plants do not need additional nitrogen right now, but nitrogen should be applied before stem elongation stage. This growth stage corresponds to Feekes growth stage 5 to 6 that may occur as early as the first week of April in southern Ohio or mid April in northern Ohio. Of course the weather will determine when these growth stages occur. There should be no need to rush out and apply nitrogen early.
In the northwest section of Ohio, wheat producers will be determining if the stands are sufficient to keep for harvest. This is because wet weather in October and seedling diseases caused severe losses in stands in a widespread area primarily west of I-75 and north of State Route 30. Some of these fields were replanted in November and December and have small plants at this time. Assessing a less than optimal stand of wheat is difficult, especially this year with plants of various ages and numbers of tillers in replanted fields. Estimating yield from numbers of tillers per foot of row this early is difficult because we do not know what the weather has in store for the crop through spring.
Yield is a function of the number of heads per acre, seed per head and weight of seed. Wheat has a tremendous capacity to compensate for stand. The largest heads with the most seed are on the main tillers, usually those tillers are produced in the fall. Thus, the more large heads the higher the yield. Counting tillers now, in March, may or may not provide a good estimate of the yield potential of a field. Wheat has the capability to produce new tillers until the stem elongation growth stage (Feekes growth stage 6) in mid April. Also, not all the tillers will develop heads. For this reason, tiller counts are relative and are only an indicator of potential yield.
In March, you will not be able to estimate the number of heads produced, since not all tillers produce heads. However, assuming each head produces 30 to 35 seed and there are 15,000 seed per lb, it will take about 40 heads per foot of 7.5" row to produce 100 bu/A. Since we cannot count heads in March, but we can count plants and tillers, we need to make some assumptions. If 9 plants per foot of row each have the capacity to produce 3 tillers, for a total of 27 tillers with heads per foot of row, the yield potential would be in the 65 bu/A range. However, if these same 15 plants only produce 2 tillers, the yield potential would be about 45 bu/A. As you can see, an acceptable yield can turn into an unacceptable yield based on how many head bearing tillers develop later this spring.
Each field should be examined individually. Those fields that have lost stand in large areas or patches present big problems and are prime candidates to be converted into another crop. Assuming there was relatively uniform loss of stand in the field over winter, we would estimate that 10 to 13 plants per foot of row would provide an economic stand at this time, especially if each plant was capable of producing 3 or more tillers. For estimating potential yield, multiply the number of tillers per foot of 7.5" row by 2.5. Obviously growing conditions this spring; fertility level, weed pressure and disease will have an impact on the actual yield. Producers should also consider alternate uses for the field (i. e. soybeans, corn, alfalfa), rotation sequences, and pest control (i.e. soybean cyst nematode infestations) when making the decision to keep the wheat or plant another crop.
Stewart's bacterial leaf
blight was negligible throughout Ohio in 2001, but it has caused significant problems
in other years. The bacterium causing this disease is carried and spread by the
Flea Beetle. During years with mild winter temperatures the flea beetle adults
overwinter in large numbers. In the spring, as corn emerges from the ground, the
flea beetles feed on the young plants and spread the bacterium which in turn causes
seedling wilt and leaf blight. The incidence of Stewart's disease is related to
the ability of the flea beetle to overwinter. More complete information on the
disease is available on the Ohio Field Crop Disease web site:
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/stewarts.htm
Flea beetle adults become active in the spring when soil temperatures reach 65 F. Adults are most active on sunny, warm, windless days. They hide in cracks in the soil during windy, cool or cloudy periods. After feeding and mating, adult females lay eggs at the base of the corn plants. Larvae feed on corn roots and are full grown in about two weeks. There are at least two generations per year in Ohio. The beetle overwinters as an adult in the soil near corn fields. It prefers bluegrass sod, but may be found in fencerows, roadsides, and woods. Additional information in flea beetles is available at: http://ohioline.osu.edu/b545/b545_14.html
The occurrence of Stewart's bacterial disease is totally dependent on the level of flea beetle survival over winter. For may years, winter temperatures have been used to predict the severity of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters. The 'flea beetle index' is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February. Index values of less than 90 indicate negligible disease threat, 90-95 indicate low to moderate levels, 95-100 indicate moderate to severe and values over 100 predict severe disease.
The 2002 flea beetle
index and predicted incidence levels for several locations in Ohio are:
Hoytville, Wood Co. = 101.5; Severe
Wooster, Wayne Co. = 104.7; Severe
South Charleston, Clark Co. = 104.3; Severe
Piketon, Pike Co. = 112.9; Severe
These
numbers indicate that flea beetle populations should be very high in Ohio and
that Stewart's bacterial disease could be severe. Time will tell if this prediction
is correct. The flea beetle index has been a relatively good predictor over the
years.
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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), Jim Beuerlein (Soybeans and Small Grain Production Specialist), Peter Thomison (Corn Specialist), Bruce Eisley (Entomology) Ed Lentz (District Agronomist) and Jeff Stachler (Weed Science). Extension Agents: Howard Siegrist (Licking & Fairfield), Roger Bender (Shelby), Greg La Barge (Fulton), Gary Wilson (Hancock) and Dennis Baker (Darke).Editor: Greg La Barge Web Editor: Tom Rosati
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