Agronomy Notes

February 1, 1998

Contents

CORN and WHEAT

- Dr. Erick Larson

Herbicide rotation restrictions - Several good years of corn production and good market prices have significantly raised interesting in corn as a rotation crop. Before rotating crops, be aware of any potential herbicide carry-over problems associated with weed-control programs. Many popular herbicides have long rotation restrictions. Planting a susceptible crop is recommended unless the herbicide rotation restriction is met, which requires planning for future crops as well as this year's crop. Past problems with Zorial and Command carry-over vividly illustrate the potential for herbicide carry-over injury. A recommendation for detecting potential carry-over is planting a "test crop", where rotation restrictions are marginal.

Soil samples may be collected and brought inside where corn, wheat, or any other susceptible species may be planted and observed for herbicide reaction. Reaction can also be tested in the field, although germination will likely be slow. Although actual field conditions may be impossible to duplicate, this should provide a reliable indicator of carry-over potential.

Early planting - Timely planting is an essential part of producing maximum corn grain yields. For numerous reasons related to crop development, early planting results in better yields than when planting late. Early planted corn's sensitive silking period, when grain yield is most susceptible, generally occurs before drought stress reaches its normal late-summer peak. Early planted corn generally also has greater opportunity to develop a deeper and more extensive root system before droughty conditions arise. Early planted corn will undergo reproductive development during a time with more available solar energy due to longer day lengths, but with lower air temperatures. Early planting often helps reduce yield loss associated with late-season leaf diseases and insect pressure. Early planted corn will also mature during August, meaning increased likelihood of favorable conditions for field drying and greater harvest efficiency due to a quicker dry-down period.

Suggested planting dates - The standard guideline for determining earliest planting date is when morning soil temperature at planting depth is maintained at more than 50 degrees F for several days before planting. Planting before the soil temperature is warm enough for germination only increases the potential for stand failure. Soil temperature may vary, depending on soil texture, slope, color, and amount and type of crop residue. Rather than relying on a predetermined date to begin planting, randomly measuring soil temperature with a thermometer within a field should provide a more reliable indicator of desirable conditions for stand establishment. Suitable soil temperatures for corn germination generally begin between February 25 and March 20 from the coastal to northern counties.

Wheat fertilization - Timing of nitrogen application plays a large role in N-use efficiency. Wheat requires about 2 pounds of N for each bushel of grain it produces. Apply approximately 25% of the total nitrogen in the fall. If wheat follows soybeans, this amount can be reduced; however, if wheat follows corn or sorghum, increase this amount to compensate for nitrogen tied up by decomposing residue. Apply the remaining nitrogen in the spring after dormancy breaks, but before the second node is visible. This generally occurs from mid-February through mid-March. Split applications in the spring often produce better results due to high likelihood of denitrification and possibly volatization if conditions are warm and wet. Limit your application of liquid UAN solution (32%) to around 50 pounds of N per application to prevent excessive leaf burning.

WEED CONTROL

- Dr. John Byrd

Most cotton producers and others associated with the cotton industry are aware that the EPA on December 24, 1997, canceled the registration of Buctril herbicide on BXN cotton cultivars. Rhone-Poulenc announced a meeting with the agency on January 23, 1998, to request a reevaluation of this decision based on new data submitted early in January. The outcome of this meeting is uncertain. If the EPA reverses its decision, growers who plant BXN cultivars will be expected to pay a technology fee to Stoneville Pedigreed Seed Company. If the decision is not reversed, growers may still plant the BXN cultivars, but may not treat with Buctril and likely will not be charged a technology fee.

Lynn Goldman, assistant administrator in EPA, told a commodity group in Louisiana January 23 that the agency made the decision to cancel Buctril without reviewing the new data submitted in early January by Rhone-Poulenc. The agency has started a new review using traditional procedures, which will require several months; however, a reversal could occur before April.

Monsanto indicated there will be settlement with some of the 1997 complaints against Roundup Ready cotton cultivars due to a typical boll formation. Monsanto and Delta and Pine Land companies will address the concerns of those affected farmers and will compensate farmers who experienced boll shed and can document that Roundup Ultra was properly applied.

Monsanto revised their guidelines for Roundup Ultra applications to Roundup Ready cotton; the revisions are on the new Roundup Ultra label. New guidelines for Roundup Ultra application state: 1) do not apply over top of Roundup Ready cotton after the fifth leaf reaches the size of a quarter; 2) sequential applications of Roundup Ultra cannot be made less than 10 days and 2 nodes of cotton growth a part; 3) apply directed sprays in a manner to minimize deposition of spray solution on cotton foliage.

Three new herbicides will not appear in the 1998 Weed Control guidelines for Mississippi; all three are Dow Agro products.

Labeled for soybeans or corn, Python WDG is an 80% formulation of flumetsulam, the broadleaf herbicide in Broadstrike + Treflan and Broadstrike +Dual, and is sold in water-soluble packets that contain 4 ounces. Application rate on fine-textured soil is 3 to 3.5 acres, 4 to 4.5 acres of medium-textured soil, and 5 acres with coarse-textured soil. Python has no postemergence activity. This herbicide can be applied preplant surface, preplant incorporated, or preemergence, but only once per year. Other precautions stated on the label include the following: do not apply more than 1.12 ounce flumetsulam per acre per season (cumulative from all products); do not apply more than 30 days before planting; maintain at least 85 days between application and harvest; do not apply to sweet corn or popcorn; do not apply to soils with pH greater than 7.8; do not graze or feed treated soybean foliage, hay, or straw to livestock; do not apply by air. Rotation intervals for crops of significance in Mississippi are peanuts, sweet potatoes, small grains, 4 months; rice, 6 months, grain sorghum 12 months, cotton 18 months; crops not stated on the label, 26 months. The label indicates partial control of morningglory species and giant ragweed, and control to light or moderate infestations of cocklebur, jimsonweed, sicklepod, and common ragweed. Python controls several species of nightshade, smartweeds, and wild poinsettia. These species are of limited significance in Mississippi corn and soybean.

FirstRate and FrontRow are new products from Dow Agro that are labeled for use in soybeans. FirstRate contains the active ingredient cloransulam-methyl (84%), and FrontRow is a co-pack of FirstRate and python. Since I don't have a FrontRow label, only FirstRate information will be given here. Application can be preplant incorporated, preemergence or postemergence. This herbicide is marketed as 1.5 ounces in a water-soluble packet. As a soil-applied treatment, the application rate is 2 to 2.5 acres per packet, or 5 acres for postemergence applications. Nonionic surfactant plus UAN, crop oil concentrate, or crop oil concentrate plus UAN must be used with postemergence applications. Weeds controlled preemergence: cocklebur, jimsonweed, annual morningglory species, pigweed, smartweed, ragweed, velvetleaf, and waterhemp. Postemergence applications control those previously listed except pigweed and waterhemp, and includes horseweed (=marestail). Precautions stated on the label: do not exceed 0.75 ounce per acre with soil applications or 0.3 ounce per acre with postemergence applications; do not make more than one application per season; do not harvest treated soybean forage or hay for 14 days after application; do not harvest soybeans less than 65 days after treatment.

SOIL TESTING

- Keith Crouse

Nitrate nitrogen in soils of Mississippi is lost through denitrification or leaching. Research shows that, under the Mississippi's warm and wet environmental conditions, the level of residual nitrate nitrogen is low. Knowing the residual nitrate nitrogen of the soil may be useful. The test is only good for the nitrate nitrogen present when your sample is collected, but is useless unless the following are considered: (1) Since nitrate nitrogen is lost throughout the year in Mississippi, take your samples before applying nitrogen fertilizer and as close as possible to planting.

(2)You must collect your samples deeper than 6 inches and to a depth of 36 inches, depending on the crop and samples taken in 6-inch increment. This is due to nitrate nitrogen being a mobile compound in the soil. Also, samples need to be representatively collected in the field, with appropriate subsamples, in order to make up one representative sample.

(3) Research in Mississippi shows that air drying samples immediately after taking was the correct procedure for handling nitrate nitrogen samples. This can be accomplished by spreading the samples out onto metal or plastic trays.

The Soil Testing Laboratory at Mississippi State can provide the results of nitrate nitrogen analysis if the appropriate information sheet is filled out and attached to the sample(s). You can get the nitrate nitrogen sheet(s) and box(es) from your local county Extension agent or from the soil testing laboratory at MSU. Cost for this service is $3.

COTTON

- Dr. Will McCarty

Seed quality should be a concern to all producers. Apparently there are ample supplies of high-quality seed of most common cotton varieties.

Know Your Seed Quality - Growers can request cool-test information, which provides good information for planting decisions. The cool test is also one of the most misunderstood of the tests for seed quality. In this test, cotton seeds are germinated for 7 days, plus or minus 4 hours, at a constant 64.4 degrees Fahrenheit (l8 degrees Centigrade). At the conclusion of the test, one count is made, and only those seedlings reaching l.5 inches long are counted. The temperature for the duration of the test must not vary by more than .5 of a degree. Constant temperature and proper interpretation are critical factors for results to be valid. Samples with a cool germination of 50 percent or greater are considered acceptable for planting; seeds with values above 60% are preferred. The cool-test germination value is an indicator of the approximate rate of emergence of that lot of seeds under adverse planting conditions. You must use a competent laboratory for the germination test. Adjust seedling rates and planting dates according to the cool test results. Plant seeds first that have the highest percent germination in this test; plant seeds with the lower germination rate later in the season.

Vigor Index - Some people use this term as the sum of the warm germ and cool germ of a lot of seed. Example: If a seed lot has a cool test of 60 percent and a standard germ of 80 percent, the Vigor indexes 140. A vigor index equal to or greater than 140 is preferred. I would rather use the actual values for cool germ and standard germ because a seed lot with a vigor index of 140 may have an 80 warm germ, and a 40 cool germ may have a 90 warm germ and a 50 cool germ. There is a difference. For more information, refer to Extension Information Sheet 1364,"Understanding and Using Results of Cottonseed Germination Test."

Variety Experiments - Information on the cotton variety trials is available for tests conducted in 1997. When selecting a variety to plant in 1998, consider several factors: 1. Yield in 1997 and yield averaged over a period of years (look for high yields and consistency);2. Yield across soil types and geographic locations (look at the data from soil types similar to the ones you farm and from locations nearby); and 3. Fiber properties, especially strength, length, and micronaire. Several varieties on the market are capable of producing high yields of good-quality cotton. When deciding which varieties to plant, stick with proven performers on the part of your acreage, but absolutely try some of the newer promising varieties to see how they perform.

Earliness - Earliness is an important factor each year, and you need to follow an overall "earliness objective." Research has demonstrated that producing an early crop increased the probability of the crop's being profitable.

FORAGES AND PASTURES

- Dr. Lamar Kimbrough

Depending on where you are located in Mississippi, cool-season forages should start some renewed growth that may have been slowed by winter cold. These forages include small grains (cereals), ryegrass, fescue, cool-season legumes, and mixtures of these. In the upper part of Mississippi, there may be little growth at this time; while in the lower part of the state, these crops may be growing well.

For continued good growth from these forages, you may need several things including: (1) adequate soil moisture, (2) fairly mild temperatures, (3) adequate soil fertility, (4) weed control, and (5) controlled grazing management.

Soil Moisture - Usually during this time, soil moisture is adequate; however, too much moisture from excessive rains may cause problems. If possible, try to keep cattle on well-drained land during severe wet weather. Excessive tramping and bogging may injure these forages and reduce the stand for good growth during the prime growing time of March and April.

Temperature - There is little plant growth at temperatures below 40 degrees F. During extended long, cold periods, cattle may need some high-quality hay or other feeds to help protect pastures. If cattle are held on frozen pastures, severe plant injury can occur. As mentioned earlier, protect these pastures for later growth.

Soil Fertility - Adequate lime, phosphate, and potash should have been applied before planting to carry the plants through the cool-season growing period. If not, you may still get a response from these fertilizer nutrients if applied now.

A balanced fertility program with lime and the nutrients mentioned is necessary for good establishment and growth from these plants. However, for the grasses, nitrogen is the element that grows the grass once a stand is established. Usually it takes about 65 pounds of nitrogen at planting and again in November or early December. You should be getting ready for a late-February application of the same amount. This sounds like a lot of nitrogen, but when the growth is removed as with grazing, these grasses can use about a pound of actual nitrogen per acre per day of grazing. The rates in north Mississippi where growth is less may be lower. Also, where good stands of legumes are grown with the grass, nitrogen rates should be lowered.

Weed Control - Several broadleaf weeds can cause problems in cool-season grazing crops. These weeds include yellow flowered buttercup, dock, and wild mustard. For information on specific weeds and herbicides, ask for Extension Information Sheet 945, "Weed Control in Forages." If you do not control your weeds, weeds will often greatly reduce desired forage production.

Grazing Management - Usually these crops are ready to graze with 6 to 8 inches of growth. Grazing shorter than 2 to 3 inches in cold weather may badly damage the stand and slows regrowth. Green leaves should remain below the grazing height.

With high stocking rates, cross fences are needed. Allow pastures to grow 6 to 10 inches, and then graze off by concentrating animals on a relatively small area. After the forage has been grazed off, move animals to another area to allow for regrowth. Electric fences can help where permanent fences are not adequate.

SOIL FERTILITY AND MANAGEMENT

- Dr. Larry Oldham

In-row fertilizer use has generated a great deal of interest this year. As in most things, success is not 100% guaranteed, but the risk of trying is not unbearable.

Starter applications will increase the supply of nutrients in the critical root zone of emerging plants, and the added N and/or P will stimulate early-season root growth. However, whether a yield response occurs will depend on the weather later in the season.

Some materials should not be placed in direct contact with seeds. These materials include ammonium thiosulfate (12-0-0-26), materials containing boron, or urea fertilizers (including 28% or 32%solutions).

Rates of materials that can be placed in close proximity depend on the salt index, which is the sum of the N and potash content of the material being applied per acre. Phosphate does not contribute to the salt index. For example, 100 pounds per acre of 7-12-7 gives a salt index of 14. Never apply a salt index of greater than 5 indirect contact with seeds The salt index can be higher as the distance between the fertilizer placement and the seed increases; however, on sandy soils, do not go higher than a salt index of 20.

SOYBEANS

- Dr. Alan Blaine

If you have not heard, there is a shortage of many soybean varieties. A lower- than-expected germination has contributed to this shortage. If you have producers who have not booked seed yet, impress upon them the importance of doing this today.

Copies of the Mississippi Soybean Variety Trials are available in the county Extension offices. In addition, we have a list of high-yielding soybean varieties and ratings for varietal sensitivity to the new herbicide Authority.

Interest in Roundup Ready soybeans is still high, but not as high as in midsummer. Although all available varieties will probably be sold, keep in mind, we do not know as much about the Roundup varieties as we would like to know.

Mississippi has two Roundup Ready locations (Stoneville and Starkville). In 1998 an additional site will be added at Clarksdale.

Although supplies of certain varieties will be limited, pay close attention to variety selection. Above-average soybean yields can be produced in Mississippi, but growers must pay attention to several production inputs. 1) Variety selection - variety selection is extremely important in producing high yields. 2) Planting dates - Early planting has and will continue to be an extremely important input contributing to improved yields. Early planting helps avoid late-season-drought conditions. 3) Crop Rotation - Yield advantages associated with crop rotation are real, and is something of which we need to take advantage. Crop rotation helps break weed and disease cycles, increases organic matter, soil tilth, improves water lodging capacity, and ultimately increases yields. 4) Take care of soil fertility. - Even though we have know the benefits of soil fertility for years, soil pH is the most overlooked input in crop production. 5) Timing of management decisions - Many factors impact crop production, but one thing is for certain, its not just any one input. Evaluate all aspects of crop protection and take care of the basics.

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