Agronomy Notes
March, 2002
Contents:
WEED
CONTROL
SOILS
AND NUTRIENT MANAGEMENT
SUMMER
PASTURE MANAGEMENT
RICE
COTTON
CORN
Dr. John Byrd
One of the general changes in the 2002 Weed Control Guidelines for Mississippi this year will be the presentation of recommendations for glyphosate in the agronomic row crop sections. In the past, if there were no more than two brand names of a product on the market, the committee listed brands and rates for each. If more than two brand names existed, herbicide active ingredient with the rates for the dominant formulation were listed, such as 2,4-D. This year, there will be several brands of glyphosate which can be applied preplant foliar for burndown and postemergence to Roundup Ready soybean or cotton. Since there will be two formulations in the market this year, a 4 lb ai per gallon and 5 lb ai per gallon, glyphosate will be listed as "glyphosate 4/5"with the corresponding rate for the 4 lb formulation followed by the rate of the 5 lb formulation with a slash (/) separating the two rates. An example as it appears in the preplant foliar portion of the soybean section: "Glyphosate 4/5 lb/gal - 16 to 64 oz/12.8 to 51.2 oz in ..."
Several popular press magazines have printed articles about the finding of a glyphosate resistant population of horseweed in Delaware. These resistant weeds required a thirteen fold increase in glyphosate rate to provide equivalent control as a susceptible population. Weed scientist at the University of Tennessee reported finding a glyphosate resistant population of horseweed near Dyersburg, Tennessee at the Southern Weed Science Society Annual Meeting. Both populations have been confirmed resistant by scientist with Monsanto. Apparently the Tennessee populations required only a six fold rate increase to obtain control equivalent to a susceptible population.
Growers should be encouraged to ROTATE herbicides. Rotation does not mean rotating Roundup Ultra with Roundup Ultra Max, Glyphomax, or Glyphos. Herbicide rotation should mean a rotation of herbicide modes of action. The selection pressure on weed populations with glyphosate has been unequaled by any other herbicide. Growers could potentially apply two preplant foliar applications, one to three applications during the season, and follow with a preharvest application.
In pasture weed control, DuPont has renamed Ally as Cimarron. Same formulation as before, a 60% dry flowable. Rates are also the same, ranging from 0.1 oz/A for control of annual broadleaf weeds up to 1 oz/A to control tough perennial broadleaf weeds. In addition, DuPont is selling Cimarron Max, a copack of Cimarron (Part A) and dicamba plus 2,4-D (Part B). This product can most easily be described as an Ally plus Weedmaster mixture. Recommended application rates are 5 oz Part A + 2.5 gallons Part B to 5, 10, or 20 acres.
Dr. Larry Oldham
Best Management Practices are doable, practical operations that make good business and protect our natural resources.
Some BMP's associated with soil and nutrient management may astonish you with their simplicity. For example, soil testing for nutrient supplying capacity is a simple, inexpensive BMP. Another BMP is simply following the fertility recommendation which accompany the results. Liming soil when needed can often be the key to opening the door to more yield and more profit.
Another BMP is developing realistic yield goals based on your soils and management system. Over fertilization is a waste of money on soils which do not have the capacity for super yields.
Selecting the proper nitrogen fertilizer for the situation and managing it properly is a BMP. Proper management includes selecting the application rate, determining how to apply it, calibrating equipment, and timing appropriately.
Be careful when applying fertilizers to avoid non-crop areas. Fertilizing non-harvested areas is not a good way to impress your banker or help the environment.
Dr. Malcolm Broome
Our summer perennial grasses (bermuda and bahia) are the forages best suited to our climate and are the most productive. Management for increased forage quality and quantity is especially important with these grasses. Many times the energy value of these grasses barely meet the requirements of the beef animal during the season. A one percent increase in digestibility or energy can result in a five percent increase in animal performance. Variety selection, proper grazing, proper fertilization and weed control will impact pasture quality.
Quite often new grass varieties are released because they produce more pounds of forage or hay per acre than other varieties. However, it is more important to know when this increased production occurs, and what quality the grass contains. For example, research shows Tifton 9 Bahiagrass produces more pounds per acre during the growing season than Pensacola Bahiagrass, but quality is the same. Warm season grasses vary in quality during the growing season. These summer grasses are highest in quality early in the season and decline from July through August. This decline in quality in midsummer can result in low animal gains or low quality hay.
The actual beginning and termination of growth of bermudagrass is controlled by temperature and day length. Night temperatures below 60 degrees F and less than 13 hours of daylight per day cause bermudagrass growth to decrease or even stop. Additionally, growth is a response to nitrogen fertilizer and rainfall occurring during the warm months causing high and low production periods. Too often fertilizer is not available in early summer when growth begins.
Proper fertilization will improve plant growth. A ton of grass with 10% crude protein contains about 50 pounds of nitrogen, 10 pounds of phosphorous, 40 pounds of potassium and varying amounts of other chemical elements such as calcium, magnesium, and sulfur needed for growth. A ton of forage will not be produced if any of these grass nutrients are lacking. Higher yields need additional nutrients to produce at an economical level otherwise less than 2 tons of dry matter can be expected on a per acre basis.
Adequate rainfall, and a long growing season in Mississippi favor weed growth in pastures. Fertilization coupled with poor grazing management will increase weed growth at the expense of grass production. Spring weeds frequently emerge and begin growth earlier than do warm-season grasses thus gaining an advantage on summer grasses for sunlight and nutrients. Data from demonstrations in improved pastures shows 2 to 7 pounds of grass was produced for each pound of weed controlled.
Proper management of warm-season pasture grasses should result in uniform, high quality forage to meet the nutritional needs of livestock. Pastures must be considered more than minimal-input crops to be utilized to their fullest potential. For more information on bahiagrass and bermudagrass contact your local extension county agent.
Dr. Joe Street
Planting:
As we shift to newer varieties, we need to reevaluate the
way we plant rice. Because of the different seed sizes of
the new varieties, plant rice seed based on the desired rate
of seed per square foot rather than the standard 90 pounds
per acre. If you plant 90 pounds of Lemont, you plant about
40 seeds per square foot, however, if you plant 90 pounds of
Priscilla, you are planting only 34 seeds per square foot.
The following table provides the guidelines for planting
forty seeds per square foot.
If you plant into a good smooth seedbed, you may reduce the
seeding rate. In research plots, seeding rates as low as 45
pounds per acre have produced the same yields as 90 pounds
of seed per acre. I am comfortable with planting 30 seeds
per square foot, but I am not yet ready to recommend
planting 20 seeds per square foot except for hybrid rice. We
do know that a plant population of 10 to 20 plants per
square foot will produce a good rice crop. If you are
planting more than one variety, watch the seed size to
ensure the proper seeding rate.
If possible, locate rice fields away from Roundup Ready soybeans and cotton. Minimize the potential for glyphosate drift as much as possible. Document any glyphosate applications around the rice field. Drift onto young rice will be readily evident and rice that survives will generally recover and produce a crop although it may be delayed. Symptoms from glyphosate drift onto rice at later growth stages such as midseason to booting may or may not be manifested until harvest.
If you plant your levees, the levee ditch should be filled in as much as possible to reduce the depth of the flood in the ditch. Levee ditch rice yields better than rice on the levee and is better quality.
Seed Treatment: Fungicide seed treatments may increase emergence if you plant early in cool weather. Fungicides may not improve emergence if rice is planted when temperatures are favorable for rapid germination. Seed borne diseases such as Brown Spot can be controlled with Thiram. Pythium can be controlled with Apron XL or Aliegence. Maxim or Vitavax controls rhizoctonia but that is generally not a problem. Vitavax also has some activity on pythium.
Zinc seed treatment may help on soils with a pH greater than 7.5, a light silt loam soil, or newly land formed fields. We have generally seen little response to zinc on clay soils.
Icon seed treatment is very effective in controlling rice water weevil. It offers partial control of chinch bug but will not control a heavy infestation. Icon also offers control of some stem borers.
DD50: The DD50 program as an excellent management tool. The program is on the Internet at www.deltaweather.msstate.edu or available through your county agent. This program is an excellent tool to use as a reminder for several input decisions. We are continuously trying to improve this program and I would appreciate any comments you have.
Dr. Keith Crouse
While knowing the residual nitrate nitrogen of the soil may be useful, the test is only good for the nitrate nitrogen that is present when the sample is collected and has very little value unless the following items are considered.
- Since nitrate nitrogen is lost throughout the year in Mississippi, take samples before nitrogen fertilizer application.
- Samples must be collected deeper than 6 inches and to depths of 36 inches depending on the crop being grown. Samples need to be taken in 6-inch increment and need to be representatively collected in the field with the appropriate number subsample in order to make up one soil sample.
- Research in Mississippi showed that nitrate nitrogen samples need immediately air-drying after taken. This can be accomplished by spreading the samples out in metal or plastic trays.
The Soil testing laboratory at Mississippi State University can provide the results of nitrate nitrogen analysis if the appropriate information sheet is completed and accompanies the sample(s). The nitrate nitrogen sheet(s) and box(es) can be picked up at a local county Extension office or at the soil testing laboratory at Mississippi State. Cost of this service is $15.
Also, as a reminder, the Soil testing laboratory prices have changed to $6.00 per soil sample and $15.00 per tissue sample. Recently, samples have been received with insufficient payment or without MSU customer identification form being completed. Even though the clientele has an account with MSU-ES Soil Testing Laboratory, they need an account with MSU Accounting Department in order to process samples as an account receivable. We have been processing these samples, but samples will be held for processing until payment or MSU Account form is received. Kept in mind we are separate from the nematodes and plant disease laboratory therefore we need separate payments for analysis.
We appreciate your assistance during this time of transition.
Dr. Will McCarty
Stale Seed-beds: It is a good idea to make burn-down applications before natural vegetation grows excessively large. This is especially true on heavy textured soils. There are several reasons for this which include: 1) smaller vegetation is easier to cover and control with lower use rates of material. 2) plants are perhaps the most efficient moisture pumps in existence. Growing vegetation can dry seed-beds tremendously fast. If spring vegetation is allowed to dry out seed-beds, additional rain will be required before planting. This is especially true for narrow rows. A narrow row bed (30 -32 inches) contains less soil volume than a 38-40 inch row. The key is to let the vegetation get large enough to provide some soil cover but not large enough to be hard to control.
In many cases the use a tank-mix including a residual herbicide may be advantageous.
Planting
Date: Determining when to plant is one of those situations
where a little knowledge must be tempered with a lot of
common sense. A general recommendation for planting date is
when the soil temperature, at the two inch depth, is 68F and
the five to seven day forecast calls for an accumulation of
50 to 60 DD60s. When does this occur? This date changes
considerably depending upon yearly weather
conditions. April
9 - 15 28.7 April
16 - 22 45.6 April
23 - 29 48.4 April
30 - May 6 53.8 May
7 - 13 71.0 May
14 - 20 85.2
Common sense must apply but the long term average indicates
that the last two weeks of April and the first two weeks of
May are perhaps the most favorable for planting. Never set a
calender date and start planting. Use soil temperature, soil
moisture saturation and weather conditions as a guide. The
first 24 to 36 hours a seed is in the soil is the most
critical. If a cotton seed imbibes cold water (in the low
50'sF) root damage may occur and emergence will be
significantly reduced. An emerged cotton seedling has a
better chance of surviving adverse weather (cool front with
an associated shower) than a sprouting seed. Remember -
common sense must apply - look at the soil and weather and
not be handcuffed to a particular calendar date.
DD60 Accumulation
|Stoneville, MS
Seeding Rates: Monitor seeding rates closely. Recent tendency has been to plant as thin as possible in an attempt to reduce per acre technology fee cost. To do this you will need to have a very firm understanding as to the quality of the seed you are planting. Be sure you know the actual germination and the cool germination of your selected seed lots. This information is available upon request and can be useful. Good quality seed should have a standard germ of 80% or better and a cool test of 65% or better. The standard germ will reflect expected field emergence under favorable conditions while the cool germ is a better indication of expected field emergence under cooler and wetter conditions.
Consider soil conditions and seed quality and plant for a final stand of 3.0 to 4.0 plants per foot of row in 38 to 40 inch rows and 2.0 to 3.0 plants per row foot in narrow rows (30 to 32 inches). This usually translates to dropping about 4 to 5 seed per foot of row in 38 to 40 inch rows and about 3 to 4 seed per row foot in a 30 inch row. Cotton planted too thick will tend to fruit a little higher and the weaker seed in the lot (later emerging) will be shaded and competition will render most of them unproductive.
Proper calibration of planters is very important. Optimum yields and crop development will generally occur at a plant population between 40,000 and 50,000 uniformly spaced plants per acre for most any row spacing. (With the exception of Ultra Narrow Rows where populations over 100,000 are needed). The more productive the soil the lower the plant population that can be tolerated, as long as spacing is uniform.
Some tips for setting a planter are:
1. Use manufacture suggested settings only as a guide.
2. After settings are made by the use guide run the planter on a hard surface such as a turn row. Measure 20 feet and count the number of seeds and divide by 20. Check several of the units, not just one. Make any necessary changes for the planter to deliver the desired number of seed per row foot. Forget about pounds of seed per acre, concentrate on number of seed per linear foot of row.
3. Forget about running the planter in the field and digging up seed for the purpose of setting plant population. You will never find all of them and the cotton will be too thick. Only use the digging method to set planting depth.
Below is a table that converts plants per row foot to plant population per acre.
Plants
/ Row Foot 8 30 38 40 2.0 130680 34848 27512 26136 2.5 163350 43560 34390 32670 3.0 196020 52272 41268 39204 3.5 60984 48146 45738 4.0 69696 50024 52272 4.5 78408 61902 58806 5.0 87120 68780 65340 5.5 95832 75658 71874 6.0 104544 82536 78480
To determine seeding rates you will need to adjust this
number by an emergence factor. For example: if you are
planting in a 40 inch row and want a final stand of about
45,000 plants per acre, from the table you will need an
average of about 3.5 living plants per row foot. Adjust this
number by actual germination and what you expect to get up.
If that number is, for example 85%, you would divide 3.5 by
.85 which would equal 4.1 seed per foot. In other words, for
that lot of seed, drop an average of 4.1 seed per row foot
for a final stand of 3.5 plants per foot, etc.
In recent conversations with the Cotton Specialists in Alabama and Tennessee, their recommended plant population is about the same as ours.
Dr. Erick Larson
Plant density - Growers should strive for 24,000 to 32,000 plants/acre depending upon mainly upon a field's yield potential, planter row width and planting date. If a corn yield goal of 200 bu./a. (50 bu./a. soybeans or 2 bale cotton) is realistic, particularly under irrigation, then strive for 28,000-32,000 plants/acre. If this goal is unrealistic, then lower the seeding rate accordingly - do not generally exceed 28,000 plants/acre in dryland culture! Also, row width changes optimum plant population because it ultimately affects plant spacing. Seeds spaced closer than six inches apart increase competition for light, water and nutrients which weakens stalk quality without increasing yield potential, particularly under stress. Thus, optimum plant population in wide rows is generally around 2,000 - 4,000 plants/acre less than narrow rows. Remember to over plant desired plant population about 5 to 10% depending upon seed germination and planting conditions. Early planted corn (soil temperature 50-55 degrees F) should be seeded slightly thicker than normal because cool spring conditions cause higher seedling mortality and shorter plants at tassel, meaning more plants are needed to intercept light. Conversely, growers should lower seeding rate with later planting dates since warm soils enhance seedling establishment, taller plants are produced and yield potential decreases.
Plant uniformity - Francis Childs, current world record corn farmer - 408 bu./a., says "Root systems and uniform stands are the foundation of high corn yields." Planter operation directly effects both these parameters. Poor corn plant spacing and seeding depth are common problems that will affect yield potential as much, or more than plant population. Research studies indicate that most growers could improve yields 5-25 bu./a. by just improving planter performance. Best of all - it may not cost you a dime to gain this improvement. The most common cause of seed distribution problems is excessive planter speed. The maximum speed for maintaining uniformity for plate-type planters is 4.0-4.5 mph and vacuum-type planters is 4.5-5.0 mph. Speeds exceeding these values will cause much poorer seed spacing and less seed depth uniformity because seeds are rolling and bouncing in the seed furrow. Corn plants are extremely sensitive to plant spacing because they do not tiller or produce branches to alter their plant size. Crowded or late-emerging plants produce small ears and spindly stalks due to excessive competition for light, water and nutrients with their neighbor. Corn seed is available in numerous combinations of size and shape which may further aggravate planting problems. Growers with plate-type planters should match planter plates with their seed size. Likewise, growers with vacuum-type planter should match disc size with seed size and match air pressure with their seed. Excessive wear to planter plates or finger pick-ups often also cause major problems - just because something worked last year, doesn't necessarily mean it will this year.
Planting depth - Many producers unfamiliar with corn seedling development plant corn too shallow. Corn seed should be planted 1 _ - 2 inches deep. Planting depth should be set in the field during planting. This is important because soil type, seedbed condition and moisture may influence actual depth. Corn seed's inherent energy and germination process ensure emergence from depths as great as 3 inches. The origination point of the nodal root system is moved upward when corn seed is not planted deep enough. Corn seed placed less than 1 inch deep will develop nodal roots at or above the soil surface. This exposes these roots to factors such as hot, dry soil, herbicide injury, and insect predation which can significant impede root development. This often leads to standability problems, nutrient deficiencies and even drought stress throughout the year. Birds may also cause stand loss by extracting shallow planted corn seeds.
Bt Refuge - Growers can plant no more than 50% of their corn acreage in Bt hybrids trademarked YieldGard which contain the MON-810 insertion event. Growers will be required to plant an equal acreage of non-Bt corn as a refuge within a half mile of their Bt corn. Neighbors' conventional corn does not count as refuge. The non-Bt refuge may be treated with insecticides (excluding sprayable Bt products) as needed. These refuge requirements for YieldGard Bt corn in Mississippi are the same as last year.
Should I plant Bt corn? - Bt corn effectively controls both Southwestern and European corn borers and has moderate control on corn earworms and fall armyworms. However, Bt corn does not control the primary insect pests during stand establishment, such as chinch bugs, cutworms, rootworms, wireworms, etc.... Thus, using a Bt hybrid will not substitute for the use of a soil-applied insecticide at planting. Preliminary research data and industry yield trials suggest the inclusion of a Bt event does not generally increase hybrid yield potential compared a closely-related conventional isoline in the absence of corn borers . Thus, a grower will not likely recover the higher seed cost of the Bt technology (about $10 per acre), unless significant corn borer infestation is likely. Unfortunately, seasonal corn borer populations are not very predictable. Thus, local historical infestation levels should be used to justify Bt hybrid utilization. Also, later than normal planting, particularly in areas with historical corn borer populations, increases the likelihood of 2nd and 3rd generation borer infestation.
Prevent stand loss - Growers who wait to apply a burndown herbicide near planting greatly increase their likelihood of experiencing stand loss from cutworms. Cutworms feed on green winter weed vegetation present in fields during the early spring. If a burndown herbicide is applied near planting, cutworms will still be present and will be forced to feed on freshly emerging corn. Thus, growers should use a labeled pyrethroid at planting or with the burndown herbicide to control cutworms, unless a granular insecticide is used at planting.
Department
of Plant and Soil Sciences
Box 9555
Mississippi State, MS 39762
Will
McCarty, Ph.D.
Extension Leader
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