Agronomy Notes

June, 2003

CONTENTS:

 

 

NUTRIENT AND SOIL MANAGEMENT

Dr. Larry Oldham

Growing plants indicate the success of a nutrient management program. This is a critical period during the growth cycle of our annual crops. For instance, most nitrogen is taken up by corn between the 5 to 6 leaf stage and tasseling.

The May rains in parts of the state have created a great deal of concern about whether applied nitrogen has been lost to denitrification or leaching. The answer depends on how much nitrogen was in the nitrate form at soil saturation, the temperature, and how long the soil was saturated. Detailed information on dealing with nitrogen loss was provided in a recent e-mail post from Dr. Larson.

If you suspect other nutrient deficiencies, realize that many causes can lead to abnormal plants in the field, such as insects, disease, or effects of acid soil syndrome. To confirm or eliminate nutrients, utilize plant samples from affected areas and apparent unaffected areas of the field, as well as soil samples from each area.

 

RICE

Dr. Joe Street

Planting: Rice is about 95 percent planted and with the exception of a few thin stands, most of the early planted rice looks fair to good. The very short season varieties such as Jefferson and XL7 may be planted until June 25 in the south delta and June 20 in the north delta. RiceTec has a program to delay payment for the late-planted rice seed until the crop is harvested so this could be a good opportunity to try hybrid rice. The cut-off date for Cocodrie and Priscilla is about the middle of June in the south and June 10 in the north delta. It is late but it is not yet late enough to use unproven production practices for planting or fertility. Flush the late planted rice to get it up as soon as possible and keep it growing as well as possible.

Fertility: Because of the cool weather in May, rice has not grown as rapidly as normal. In many cases, pre-flood fertilizer application has been delayed because of the small rice or wet conditions. Unless the field can be flooded in two to three days after fertilizer application to wet soil, it is better to flood the field and apply fertilizer in two to three applications directly into the flood. With Cocodrie, it is important to get at least two-thirds of the fertilizer on prior to midseason. Under normal weather conditions, Cocodrie will reach midseason in 42 to 45 days after emergence, so watch the calendar or the DD50 predictions for joint movement and midseason fertilizer application.

Weed Control: With the wet weather in most locations, soil applied herbicides have provided effective grass control but grasses are beginning to emerge. Clincher, Regiment and Ricestar are available to control the grasses. Clincher must have adequate soil moisture for effective control.

Clearfield rice acreage has increased this year. Although it is preliminary at this point, it appears that under cool wet conditions, Newpath may injure or kill some of the weaker plants. This has not been reported in other states and it may be related to a disease/environmental/Newpath interaction.

Glyphosate drift is a widespread problem this year. If the young 3 to 4 leaf rice survives the initial drift, delay the flood or hold a shallow flood and the rice will normally recover with only slight yield reductions. Glyphosate drift may delay the crop 8 to 10 days.

Glyphosate drift at midseason can cause blank heads similar to straighthead and significant yield reductions can occur.

Insect Control: If Icon was not used as a seed treatment and water weevils have been a problem in the past, apply Karate or Mustang Max within five days after flood. For the late-planted rice, watch for chinch bugs and flush if needed.

Disease control: Pythium seedling disease is occurring in some locations because of the cool wet conditions. This situation has been enhanced by glyphosate drift and weaker seedlings are not surviving. If pythium seedling disease occurs, flood the field as soon as possible. Pythium thrives in cool saturated soils but not flooded soils.

 

FORAGES AND PASTURES

Dr. David Lang

Year-Long Grazing Systems - Twelve month grazing is feasible in much of Mississippi through utilization of cool and warm season forages. A typical southern forage availability chart is shown as a proportion of annual growth. Bermudagrass and/or dallisgrass grows well in a mixture with tall fescue in much of the upper two thirds of Mississippi and on adapted soils throughout the region. Legumes, mostly clovers, but also alfalfa, have been grown successfully with the bermudagrass/dallisgrass/tall fescue mixture. Bahiagrass provides reliable permanent summer pasture, but it generally grows as single species on sandy soils, as its dense sod is usually too competitive for an accompanying cool season perennial grass. Annual clovers and annual ryegrass can be successfully oversown into each of these pasture situations.

In order to establish a warm season/cool season forage mixture the warm season component should be established first. This is because warm season grasses slow down their growth during the fall when cool season grasses need to be established. Warm season grasses are less shade tolerant than cool season grasses and their growth is suppressed into late spring by the cool season grass. Warm season grass establishment generally requires a prepared seedbed while cool season grasses can be sod-seeded into summer grasses.

A successful sod-seeding of annual ryegrass, clovers or tall fescue requires that the summer grass be grazed off closely in the fall. A herbicide burndown may also be helpful, particularly on bahiagrass in south Mississippi. In north Mississippi, however, a herbicide may not be needed if the summer grass top growth is removed. Tall fescue is a good choice in north Mississippi as it is a perennial and will not need to be replanted each year. Older types of tall fescue have a toxic endophyte which lives inside the stems, leaves, and seed. This toxic endophyte causes poor animal performance, reduced weight gain and lower calf crops. The endophyte allows the tall fescue plant to survive our hot and drought-prone summers. That is why endophyte free tall fescue did not persist when it was introduced in the 1980's. Fortunately, non-toxic endophytes have been placed in some newer varieties of tall fescue. These are marketed as MAXQ by Pennington Seed and ARKPlus by FFF Cooperative.

A cool season grass will suppress early summer growth of the warm season grass. It's important to remove or graze off the tall fescue or ryegrass by late May in north Mississippi and by early May in the south. A cool season/warm season mixture will nearly double your forage growth so make plans now to add a cool season forage to some of your warm season pastures.

 

CORN

Dr. Erick Larson

Wet Soil N Management: Wet, saturated and/or flooded conditions during much of May has raised numerous questions concerning nitrogen loss and management recommendations for corn and other non-legume crops. Nitrogen loss resulting from saturated conditions and flooding occurs primarily through denitrification, particularly in heavy soils. Denitrification occurs when nitrate nitrogen is converted into nitrogen gas by microorganisms and escapes into the air. Warm soil temperatures accelerate this process. Research indicates denitrification rates range from 2-3% per day at soil temperatures from 55-65_ F or 4-5% per day if soil temperatures exceed 65_ F. (Hoeft, 2002 - Illinios). Timing of nitrogen application and fertilizer source will affect the amount of applied nitrogen that will be subject to loss in the nitrate form. Growers who utilize UAN-solution (n-sol) can expect about 50% of the nitrogen to be converted to nitrate one week after application, 70% after two weeks, and 90% or more after 3 weeks. Therefore, you can estimate nitrogen loss by multiplying the nitrogen applied by the percentage converted to nitrate, then by multiplying this result by the number of saturated days times the denitrification rate.

Example:

A grower applied 200 lbs. of N (UAN) two weeks prior to the saturated conditions. The field has been saturated for 10 days. Soil temperature has been about 65º F. How many pounds of nitrogen have been lost?

200 lbs. of N * 70% converted to nitrate = 140 lbs. of nitrate nitrogen

140 lbs. of nitrate nitrogen * (10 days * 4%) = 56 lbs. of nitrogen loss

Growers can use these estimates to help make additional nitrogen application rate decisions. However, growers should realize the yield potential of this crop will likely be reduced because flooding/saturation inhibited root growth, stunted vegetative development, and promoted crown rot, and other diseases which may appear later, including crazy top. Thus, supplemental nitrogen application may not be warranted if growers have already applied their seasonal allotment. In the example noted, this field still has enough nitrogen available to produce a corn yield of around 110-140 bushels per acre. Thus, this grower may not need additional nitrogen because this is a realistic yield goal. Growers who have not applied their intended nitrogen allotment may be forced to apply nitrogen by air because the corn may be too tall to permit ground equipment. However, nitrogen should not be applied to saturated soils. Ammonium nitrate is the preferred nitrogen source for aerial application because it is not subject to volatilize, compared to urea. Granular nitrogen fertilizer sources will burn plant leaf tissue where granules lodge in the whorl. Thus, application should be limited to around 200 lbs. of fertilizer per acre if the corn is less than three feet tall or 100-150 lbs. per acre if the corn exceeds three feet tall.

Scouting Needs - Producers should continue scouting fields for potential problems and management decisions throughout the entire growing season. Numerous cases of off-target glyphosate drift began appearing near the end of May, particularly on young grain sorghum and other crops in the north Delta region. This growing season has also presented more problems than past years with various insect pests. Producers with irrigation capacity should monitor soil moisture status nearly daily during the sensitive early reproductive period. 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.

Irrigation needs - Corn's most critical and largest moisture requirement occurs during a four 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 - 8 percent per day due to water deficit during this period. Thus, insufficient irrigation water or slight delays can quickly reduce yield potential and evaporate profitability. Corn plants use about 1.50-1.75 inches of water per week during peak water use, so producers nearly always must supplement rainfall with irrigation to meet crop demand during this extremely critical period. Therefore, growers using irrigation should begin incrementally meeting crop demand before irrigation system capacity cannot replenish soil moisture, especially with center pivot irrigation systems.

 

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 upon moisture around the boot stage. The boot stage 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.

 

SOYBEANS

Dr. Alan Blaine

The state soybean crop as of late May was 83 percent planted. Although growers in some areas will not believe planting progress thus far, this crop as a whole is early. Exceptions are areas that are experiencing flooding and Northeast Mississippi. Once again it has been observed there in no substitution for early burndowns, often regardless of tillage plans. Whether you are going to plant no-till or not, it is beneficial to eliminate unwanted vegetation early, allowing you to better control time of planting.

Earlier burndowns may help eliminate insect populations, in no-till fields. Burning down early removes a potential food source/home for many pests and may aid in moving them from fields before the crop emerges. The need for early burndowns is further evidenced by the lack of control on large weeds and the effect of moisture on planting. Most would not have figured (they would need a rain in less than a week after getting in the field for the first time in North Mississippi) that they could use a rain so soon. The effect of wide scale field preparation and a good north wind has made soil moisture and conditions deteriorate rapidly.

Moisture became marginal early, and in some areas growers planted deep, even on early plantings. If using the early-planting option, you need to eliminate the urge to chase moisture prior to May 1. Rains prior to early May are often big rains and a tremendous detriment to soybean emergence. Many growers stopped planting due to a lack of moisture, but most would have been better off to plant shallow and wait for a rain. Soybean seed can stay in dry, cool soil for a long time. Even if day temperatures reach the low 90s and our nights cool off into the 70s, seed can remain viable for quite a while. Keep this in mind in the future. Planting shallow early will minimize replanting.

We still see fields where replanting is needed when we attempt to out guess mother nature and do not use the proper seed treatment. We also continue to see some scattered problems with the low rate of Apron. On heavy clay soils, we have doubled the Apron rate and are quite impressed. This option can solve this problem for only a few cents per acre.

Several calls have come in regarding plant populations. Our recommendation for row planting is 75,000-125,000 plants per acre. Populations 25 percent above or below this will have little impact on yield. However, the key is adequate weed control. If plants are healthy, it is usually better to keep a 50 percent stand than replant. Soybeans have a tremendous capacity to compensate for thin stands. The down side is slower canopy closure, but having Roundup Ready soybeans and irrigation makes this decision much easier.

The biggest concern in recent weeks has been playing catch-up with most herbicide applications. In some areas spraying has been delayed for 3-4 weeks due to wet field conditions.

Weed emergence has been erratic but with higher than average Roundup Rates most situations can be adequately controlled. Tank mixes are an option to be considered but that depends entirely on species/size. In most situations morningglories and prickly sida (teaweed) are the primary weeds causing the most concern when considering a tank mix. A lot of options exist but the most cost affective is probably a Roundup/Reflex tank mix(Reflex at 4ozs/acre). Classic, First Rate and Front Row are popular options but pay attention to cost. Numerous options are available for use, but you can just up your Roundup Rate and dig out of a mighty deep hole.

 

COTTON

Dr. Will McCarty

The 2003 crop is off to about the most non-uniform start I have witnessed. The only year that comes close to is 1991, but I think this year may be even more non-uniform and erratic than that year. This is definitely the latest planted crop since 1991...not by choice but by weather dictate. Rains and flooding conditions prevented and delayed initial planting and caused more replanting than in many years. It seems that drift injury has taken a higher toll than normal. However, it is not over till it's over and there is a lot of time left to make a crop, but all the free board has been removed.

Side-dress Nitrogen - Be careful with rates of side-dress nitrogen and total nitrogen in general. Excessive rates of nitrogen will delay maturity while reducing yields and quality. I think growers are doing a better job now (compared to a few years ago) matching nitrogen applications to nitrogen needs. Important - I encourage you to make your side-dress applications as fast as you can. I don't think there is such a thing as putting out side-dress nitrogen too early; avoid late applications. All cotton should have all nitrogen applied before the end of June. If you planted late (late May early June) apply all your nitrogen in one application - don't waste time splitting nitrogen and increasing risk of late applications. Also, on late planted cotton go ahead and apply your normal rate.

In cases where you fear loss of early applied nitrogen be very cautious about adding additional N. It has been my experience that N loss is normally less than we expect and making a large supplemental application can lead to problems. The exceptions are fields that were flooded after applications were made. Seek sound advice on a field by field bases before you apply extra nitrogen to cotton. It is much easier to add some at a later date than to wish you did not have it out there.

It takes about 50 to 60 pounds of supplemental nitrogen per bale of production and on sandy loam to loam soils and about 60 to 70 pounds per bale on clay loams or heavier soils. If some of your cotton is on new cotton land, or has been in corn, rice, or soybeans for several years, or is just strong land, those rates may be reduced by 20 pounds and even 50 pounds in extreme cases. If you are planting cotton into a field where moisture is available and rapid, rank growth has been a problem; evaluate your nitrogen program carefully. Do not take the attitude that you can put out any rate of nitrogen you want and control growth with mepaquat chloride (PIX Plus, etc.). PIX Plus is a great material and a good management tool, but this is not the way to use PIX Plus or to grow cotton.

I receive many questions about the use of mepaquat chloride (PIX Plus, etc.) plant-growth regulators; there are several options as to how to use this product. These decisions must be made on a field-by-field basis. This product, or similar products, will not substitute for good management or make a poor crop into a good crop. Under good management, however, I feel this product can improve plant efficiency and increase earliness. That factor makes this product a likely practice in hail damaged cotton or late planted cotton. This year, thus far, cotton has developed slowly due to cool temperatures in May. This factor may indicate that this may be a year where the use of mepaquat chloride has a higher probability of success. Proper use should be based on yield history, plant development, fruiting, and crop status. Plant monitoring goes hand in hand with mepaquat chlorate (Pentia PIX Plus, etc.) use. I feel a key to successful use is to not let the crop become vegetative (with heavy fruit loss) before implementing a plant-growth-regulator program. Once the crop goes vegetative and fruit is shed, it is difficult to "bring back" into fruiting and, so to speak, be brought under control. For Mississippi, generally, the best approach to successful use of PIX Plus involves an application at first bloom and a follow up application in 14 days if needed. Rates should be based on field needs.

Roundup Ready Cotton - Apply Roundup Ultra, Touchdown or other glyphosate herbicides to Roundup Ready cotton according to the all directions on the label. If applications are made in accordance with label instruction, no plant injury should occur. A major concern in making Roundup applications is drift onto non-Roundup Ready crops, or onto cotton that is past the size limits for over-the-top applications. Drifting Roundup onto Roundup Ready cotton that is past the labeled recommended size for OT applications may cause reduction in fruit set on lower branches. Use all precautions to ensure drift is minimized. If conditions will not allow safe OT applications, move on to directed applications. Again, when making directed spray applications of glyphosate materials to Roundup Ready cotton it is essential that all directions and cautions on the label are read and followed. Using traditional materials such as fluometuron, prometryn, diuron, Aim, Cobra and/or MSMA can add to the effectiveness to a directed spray weed program and add residual control to the program. Directing with and laying-by with residual herbicides is a sound weed control program in conventional and Roundup Ready cotton.

Hail Damage - We have not had much problem thus far in 2003, but every year some fields are hit by hail. Making decisions about a field of cotton after a hail is often a difficult decision. However, one of the most important questions to ask is, what variety is it? Today tools like Bt varieties and boll weevil eradication have made hail damage management decisions much easier. 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. With tools as mentioned it is now possible to economically manage a stand that will be late maturing due to suffering hail damage. A few years ago that was not the case. Once cotton is up to a stand and establishing a root system, it is very difficult to kill. It really is amazing how much damage a cotton stand can take and then recover. Recovery requires time which translates into later maturity. It is rare that 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 subjected to the problems associated with late cotton, that is, insects, weather, and increased production cost 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 the date is after the first of June and the number of plants that are damaged to a degree such as to make survival unlikely is so great that the plant population will be below 20,000 plants per acre with numerous skips, destroying the stand may be in order. If the survivable plant population is greater than 20,000 plants per acre, and the stand is uniform I would keep it. (Keeping in mind that 20,000 is not a number set in stone and may vary a little either way) Plants with damaged terminals will produce vegetative branches that will set fruit. Maturity will be delayed, and management must be adjusted for a late crop.

If the weather turns favorable after a hail storm event, plant recovery will be phenomenal. One of the reasons for this is that the root: shoot ratio has changed tremendously. The plant should have the same size root system after the hail storm event as it did before the hail; however, the shoot, or leaf area, will be greatly reduced. The fact that the leaf area is reduced and injured is one of the reasons why attempting to foliar-feed hail-damaged cotton has not been successful. No miracle cures can be sprayed on the fields to increase survival or yields.

 

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

Will McCarty, Ph.D.
Extension Leader

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