Agronomy Notes

June, 2002

Contents:

FORAGES AND PASTURES
CORN
GRAIN SORGHUM
RICE
COTTON

 

FORAGES AND PASTURES

Dr. Malcolm Broome

Warm Season Annual Grasses

Under the current weather pattern, about two-thirds of Mississippi's warm-season annual grasses could offer extra grazing or hay. Warm-season annual grasses can be grown from seed and are utilized during the spring and summer months, quite often as temporary forage for stockers and mature cows. These annuals provide excellent grazing for dairy cows, especially in the warmer months when perennial grasses often decline in quality. Horses may also be grazed on these annuals except the sorghum x sudan hybrids.

Despite their high establishment costs and more intensive grazing management, warm season annuals offer several advantages over perennial warm season grasses such as faster growth and higher yields and quality. All summer annuals need a pH of 5.8 or higher. Weeds are generally not a problem with these forages. If weed control is needed, contact your county MSU-ES agent for the current recommendations. A description of several summer annual grasses follows.

Pearl Millet (Pennisetum glaucum)

Pearl millet is a tall growing, erect grass that produces several stems from a central plant. It tolerates well-drained acid soils better than sorghums but does best with a pH of 5.8 or higher. When planted in late April, it should be ready for grazing in 30 to 40 days after planting and provide grazing for about 90 days. Its greatest growth will occur during the first 60 days. An acre of pearl millet will use about 150 to 200 pounds of nitrogen (N) per acre. Soil test to determine pH, phosphorus and potassium needs. Apply 60 pounds of N per acre at or shortly after seeding with another 40 to 60 pounds per month for a total of three applications. As growth slows, N rates should be reduced accordingly, especially if moisture is limited. Nitrate accumulation can cause toxicity problems under periods of low moisture and high rates of nitrogen fertilizer. A laboratory analysis should be used if this condition is suspected.

If productive stands are to be maintained, grazing should not begin until the plants are 18 to 24 inches tall. Graze to a stubble height of 6 to 8 inches, then remove animals and allow the millet to regrow before grazing again. Properly fertilized pearl millet should have a stocking rate of three to four stocker calves or two mature cows per acre during the first 60 days. As the season progresses, the stocking rate should be reduced. Based on these stocking rates, additional (May and June) plantings could be used to provide more uniform, quality grazing. As the April planting is declining, the May or June plantings will be in peak production. Seeding rates are 12 to 15 pounds per acre drilled about inch deep or 25 pounds per acre if broadcast. Several hybrid millets are sold in Mississippi.

Browntop Millet (Panicum ramosum)

Browntop millet, which can be used for hay or gazing, produces lower yields than pearl millet resulting in less forage. Due to its reseeding ability and long period of seed viability in the soil, browntop can become a weed if planted on row crop land. Browntop millet is best seeded broadcast at 20 to 25 pounds per acre on a prepared seedbed in late April or early May.

Sorghum x Sudangrass Hybrids

Sorghum x Sudangrass hybrids are tall-growing annuals similar to pearl millet in growth habit, yield and stocking rate. They tend to grow best on fertile soils and are more productive in late summer than millet. These hybrids can cause prussic acid poisoning of cattle when young forage is grazed after severely dry weather or when cold temperatures limit growth. As with the pearl millets, nitrate accumulation can also occur. Prussic acid poisoning requires grazing management be utilized, which is a disadvantage for the sorghum x sudangrass hybrids.

Seed sorghum x sudangrass hybrids into a prepared seedbed at the rate of 20 to 25 pounds per acre drilled or 30 to 35 pounds broadcast. These hybrids respond to high rates of fertilizer. Therefore, apply a complete fertilizer according to soil test recommendations before planting. As with millets, apply 60 pounds of nitrogen about every 30 days during the growing season.

With good grazing management, plants should remain leafy, however if plants become stemmy, clip them to a 10- to 12-inch height. Several thin stemmed commercial varieties are available. Thinner stems are an advantage to the thicker-stemmed varieties when cutting for hay.

Sudangrass (Sorghum bicolor)

Sudangrass is another warm season annual grass that produces lower yields than millet or the sorghum x sudan hybrids. Newer varieties have been developed that produce satisfactory yields and possess quality comparable to the millets. Sudangrass is not planted on many acres in Mississippi and can be used for either hay, grazing or silage.

Sudangrass also performs best on a well-drained fertile soil and should be fertilized as the sorghum x sudan hybrids. This grass needs a minimum of 65 degree F soil temperatures before planting. Two different plantings about 4 to 6 weeks apart should provide forage throughout the summer. Sudangrass is seeded at 20 to 25 pounds per acre drilled and 30 to 35 pounds per acre broadcast.

Crabgrass (Digitaria sanguinalis)

This low-growing reseeding annual grass is present in most cultivated fields and pastures in the state. It is most often used to furnish summer grazing following winter annuals like ryegrass or small grains. Crabgrass is highly dependent on good soil moisture conditions for best growth. The forage has excellent digestibility and is also very palatable. Generally, it will provide grazing from May until early fall. Red River is the only commercially available variety.

Harvesting for Hay

All these annuals, except browntop millet and crabgrass, should provide two or three cuttings of hay. Browntop or crabgrass generally don't produce enough forage to justify their use for hay except in special cases such as excess forage or shortage of hay. Harvest these other annual grasses when they are 30 to 40 inches tall, but don't cut any closer than 6 inches. This stubble height will aid in holding the cut forage off the ground, thus improving air circulation and speeding drying. In addition, this height allows for faster regrowth of the plant.

Weather is often a problem in getting enough time without rain for these annuals to be used for hay. A cutter-conditioner is recommended for these annuals since they have large stems that are high in moisture. Crushing the stems helps shorten the drying time. Moisture content should be 18 percent or lower before baling. Without a conditioner, it may be 5 or 6 days from cutting until baling.

Additional information can be found on summer annual grasses in MSU-ES Info. Sheet 1616.

CORN

Dr. Erick Larson

Irrigation needs - Corn's most critical and largest moisture requirement occurs during a 4-week period following tasseling, which should occur during June and early July for most of Mississippi's crop. Potential corn yield can be reduced up to 4 to 8 percent per day due to water deficit during this period. Thus, slightly delaying irrigation can quickly reduce yield potential and evaporate profitability. Corn plants use up to 1.75 inches of water per week during peak water use, so producers usually must supplement rainfall with irrigation to meet crop demand during this critical period. Begin incrementally meeting crop demand before irrigation system capacity cannot replenish soil moisture, especially with center pivot irrigation systems.

Scouting Needs - Producers should scout fields for potential problems and management decisions throughout the entire growing season. Producers with irrigation should monitor soil moisture status nearly daily during the sensitive early-reproductive period. This growing season has presented more problems than past years with various insect pests. The first generation of Southwestern corn borers was substantially higher than normal this May. Thus, corn growers may have their hands full dealing with these destructive pests during the second generation, which should occur late this month. Southwestern corn borers are an historical problem, particularly for the Delta and northeast Mississippi counties. Borers require intensive, timely scouting to diagnose, quantify and control. Corn borers are particularly hard to control since insecticide contact is virtually impossible after the insects bore into stalk, ear and leaf tissue. Thus, insecticide application timing must occur precisely during peak corn borer egg hatch to obtain effective control. Scouting should also reveal fertility deficiencies and prevalent weed competition problems.

Weed problems can often be suppressed by applying various timely layby treatments. Although control options become limited the taller corn becomes, scouting does provide insight into future problems. This diagnoses of weed history is important for future crops because corn weed problems can usually be more effectively and economically addressed with preemergence, rather than postemergence treatments.

Section 18 Exemption - Mississippi received a Section 18 emergency exemption permitting use of Intrepid 2F insecticide on field corn for control of Southwestern corn borer. This product should help improve corn borer control. It has a much longer residual activity than other labeled insecticides. Applications can be made until September 30, 2002.

GRAIN SORGHUM

Dr. Erick Larson

Irrigation timing - Grain sorghum is very drought tolerant. However, it will respond positively to supplemental irrigation during droughty conditions. These characteristics make grain sorghum well suited for limited irrigation. Grain sorghum is most dependent on moisture around the boot stage, which is characterized by the head swelling inside the flag leaf sheath, immediately prior to heading. Grain sorghum water use is maximized from rapid vegetative growth stages through the soft dough stage. Water use during this time typically peaks at about 1.5 inches per week. Water use rapidly declines after the soft dough stage. Therefore, a furrow-irrigation application just prior to the boot stage, followed by another at bloom (if needed) should provide nearly the entire yield potential of full irrigation. Center-pivot irrigation systems typically require several applications since total water application is limited (compared to furrow irrigation) by runoff potential.

RICE

Dr. Joe Street

Fertility - Much of the early rice is flooded and doing well. Remember, Cocodrie, which is the most widely planted variety this year, will reach midseason quicker than expected. With average weather, Cocodrie will reach 0.5-inch internode in 42 to 45 days. Last year many growers were late with the mid-season fertilizer application. If you do not have a DD50 prediction, watch the calendar and start checking at about 40 days after emergence. If Cocodrie is being grown on silt loam soils, it should be drained for straighthead. With the short time between flood and midseason with Cocodrie, it may be difficult to drain and dry the soil prior to midseason. Cocodrie is very susceptible to straighthead and should be drained on silt loam soils or soils with arsenic levels above 7 parts per million.

Last year, phosphorus deficiency occurred in several fields. Phosphorus-deficient plants may have purple tipped leaves and are generally darker green and tiller less than non-deficient plants. Those symptoms are usually most pronounced just after flooding, because the healthy plants respond to the pre-flood nitrogen and the phosphorus-deficient plants will remain stunted and do not tiller. Phosphorus deficiencies can be corrected even after flooding by dropping 100 pounds of 0-46-0 or 100 pounds of DAP into the flood water. The best time to apply phosphorus is prior to planting or to a rotation crop such as soybeans.

We generally don't see much zinc deficiency on the heavy clay soils, but on silt loam soils, zinc deficiency can occur. Zinc deficiencies can be expressed in several ways, but the most common symptoms are bronzing and drooping leaves after flooding. About 3 to 7 days after flooding, the leaves will become yellow and start dying. To correct the deficiency after flooding, drain the field and apply 3 to 5 lbs. of the zinc. Reflood the field after zinc application.

Insect Control - If Icon seed treatment was not used and water weevils were present last year, expect to have water weevils again. This year, Fury has been added to the insecticide arsenal along with Karate and Dimilin. The insecticide should normally be applied from immediately prior to flood to 5 days after flooding when adult water weevils are present. With the cold weather in May, the water weevils are not moving as much as usual so watch for the adults or at least check for feeding scars before treating. Expect water weevil populations to be higher and do more damage in thin stands. If root pruning becomes severe, the only option is to drain the field.

You may have read the article in Rice Journal concerning the tolerance of Cocodrie and Wells to rice water weevil. Cocodrie and Wells do seem to be able to tolerate a fairly high population of water weevils before yields are reduced, however John Bernhardt, who did his work on silt loam soils, does think it takes fewer weevils to reduce yields on clay soils.

Jim Robbins at DREC has research underway to evaluate this on clay soils. Last year he obtained a good yield response with treatments on Priscilla and Lemont but the Cocodrie location had a very light population of weevils and yields were not reduced. He is continuing to evaluate varietal response to water weevils this year.

Weed Control - With the high winds and cool temperatures, post-emergence weed control has been difficult. The soilapplied residual herbicides performed fairly well in most cases, but where grass escaped, finding an opportunity to apply a herbicide was difficult in many situations. Regiment received a full label this year for use in rice and has been effective on the large barnyardgrass. While it is always better to control small weeds, Regiment can be used on larger barnyardgrass. It has no activity against sprangletop or broadleaf signalgrass, but Regiment will control several broadleaf weeds including hemp sesbania, joint vetch, dayflower and smartweed. At higher rates (18 grams/Acre), Regiment will suppress barnyard grass from the 4-tiller stage to booting. Regiment can be applied to rice after the 3-leaf stage of development until the panicle initiation stage. Regiment can be tank-mixed with several broadleaf herbicides to expand the weed control spectrum. Add a Valent-approved silicone based surfactant to Regiment.

Ricestar also has a full label this year and is effective against 4-leaf grass including barnyardgrass, sprangletop and broadleaf signalgrass. Ricestar can be tankmixed with Whip 360 to increase activity on larger grasses. Ordram is still available for grass control and is very effective where the flood can be maintained.

Clincher received a full label in late May for use in rice. Clincher is effective against most grasses in rice and can be applied to rice from the 1- to 2- leaf stage up to 60 days prior to harvest. Clincher can be applied to up to 4-leaf grass prior preflood or it can be applied to tillering grass after flooding. The use rate is 13.5 to 15 ounces per acre plus one quart of crop oil concentrate. Clincher can be tank-mixed with Pendimax, Facet or Command. The weeds must be actively growing for maximum activity from Clincher.

COTTON

Dr. Will McCarty

Hail Damage - Every year some fields are hit by hail. Deciding what to do with a field of cotton after a hail storm is often a difficult decision. However, one of the most important questions to ask is "What variety is it?" Prior to the availability of Bt varieties and the advent of boll weevil eradication, economics of keeping and protecting a stand of cotton that was going to be very late was a much larger consideration than simply a matter plant-stand survival. Now, with the use of these tools, it is possible to economically manage a stand that will be late maturing due to hail damage. It is very difficult to kill cotton once it is up to a stand and has established a root system. It really is amazing how much damage cotton can take and still recover. Recovery requires time, which translates into later maturity. It is rare hail will completely destroy or "kill" a stand of cotton - HOWEVER- it can and has happened.

When looking in a hail-damaged field, examine the plants to see what percent have a terminal, what percent do not have a terminal, and what percent are cut off below the cotyledon node. Those cut off below the cotyledon node will probably not recover. Those that do not have a terminal will probably recover but produce a crazy plant with many branches. These plants can produce cotton but will mature late and be subject to the problems associated with late cotton--insects, weather and increased production costs with low potential returns.

Examine the stems of seedlings that survive. Stem damage may be severe enough to cause lodging later in the season. As the season progresses, additional considerations include the following: How strong is the soil? Where in the state is the field located, north or south? What is the variety in the field?

If it is after the first of June and the number of plants damaged enough to make survival unlikely results in a plant population below 20,000 plants per acre with numerous skips, destroying the stand may be advisable. If the survivable plant population is greater than 20,000 plants per acre, and the stand

 

Department of Plant and Soil Sciences
Box 9555
Mississippi State, MS 39762

Will McCarty, Ph.D.
Extension Leader

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