Cotton -- The University of Georgia









UGA Georgia Cotton Newsletter

April 19, 2002 - Click here for a printable copy

In this issue

  • Planning for Fiber Quality
  • Replant Riddles
  • Dual Magnum in Georgia Cotton
  • Selecting a Glyphosate Product to Apply Over-the-Top of Roundup Ready Cotton
  • Insect Scouting a MUST
  • Hubbub about Glyphosate Formulations
  • Generic versus Basic Manufacturer: Approach and Implications
  • Planning for Fiber Quality (Jost) Poor fiber quality resulted in some severe price discounts in parts of Georgia in the 2001 crop. This has left many producers asking what can be done to prevent this from occurring again. While there is no magic bullet for premium fiber quality, there are a few agronomic inputs that can be made to help a crop produce quality fibers. The following is a discussion of fiber quality measurements, factors influencing those parameters, and what growers can do to enhance them.

    Fiber length. Fiber length is measured in 32nds of an inch, with the base being 34 (or 34/32nds). Discounts for fiber length are also related to color grade; specifically, as color grade decreases, discounts for fiber length increase. Within a color grade of 41-4 a length of 34 will incur no discounts or premiums. However, a 33 will incur a discount of 3 cents/lb, a 32 will be deducted 6 cents/lb. Thus, a bale classed at a 41-4 with a length of 33 costs the producer $14, a 32 will cost the producer $28 (based on a 480 lb bale). If a grower produced 2 bales/A on 500 acres, that would cost $28,000.

    The length of the cotton fiber is a highly heritable trait, which means that the variety selection plays a large roll. Choosing a variety with a history of producing long fibers is the first step. Quality and yield data for many varieties evaluated over several locations are available on the UGA cotton web site.

    In addition, the length of the fiber in a boll is determined in the first three weeks after the flower blooms. In Georgia, depending on the environment, cotton will normally bloom for 4 to 6 weeks. Therefore, fibers are elongating for 7 to 9 weeks of the growing season. Any stress such as inadequate fertility or drought, has the potential to reduce fiber length. Therefore, a solid fertilizer and irrigation (where possible) program can help to attain maximum fiber length. Minimizing stress during this time period should be a primary goal.

    Finally, defoliation timing also has the potential to affect fiber length. Though typically not a common practice in Georgia, terminating a crop too early can arrest the development of young bolls reducing their fiber length.

    Microniare. Micronaire is a quantification of fiber fineness or thickness as measured by air permeability of a fiber sample. A sample of thin fibers will have a high surface area to mass ratio thus allowing less airflow resulting in a lower micronaire reading. A sample of thick fibers will have a low surface area to mass ratio thus allowing more airflow resulting in a higher micronaire reading. The base for micronaire is 3.5 to 4.9. In Georgia, if we deviate from the normal range, we typically have more of a problem with high micronaire. A micronaire reading greater than 4.9 but les than 5.3 will result in a 4 cent/lb deduction. Micronaire readings greater than 5.3 will incur a 6 cent/lb penalty. Therefore, a bale classed at a 33 staple length and a 5.2 micronaire would cost the producer $33 (a $14 deduction for staple and just over $19 for high mic).

    Fiber thickness or micronaire is also a heritable trait, thus variety selection again is a factor. Agronomic inputs can also affect micronaire. A poor boll set whether due to weather or pest pressure is often associated with high micronaire. Insect management, fertility, and irrigation can influence boll set. A cotton crop that has early, mid and late season bolls will have a better chance of lower micronaire readings than one that produces just an early crop. Defoliation timing can also influence micronaire. A crop that is defoliated at 50 to 60% open boll will have lower micronaire reading than one that is not defoliated until 80 or 90% open boll.

    Uniformity. Uniformity is a ratio of fiber lengths. The fiber length reported on grade sheets is actually the upper ˝ mean length, or the average length of longest ˝ of the fibers in a sample. Uniformity is the ratio of the upper ˝ mean length to the average length of all the fibers in a sample. Indirectly, the uniformity ratio, quantifies the amount of short (less than ˝ inch) fibers. Short fibers are difficult to spin and are thus unwanted by the mill industry. The base range for uniformity is 80 to 82. Discount for a low uniformity, for example 79, is only 0.35 cents/lb. However, not considered in this discount, is the reputation cotton grown in Georgia has gained as having low uniformity, which has led some U.S. mills to have a bias against Georgia cotton.

    Timely harvest that prevents weathering of fibers in the field is probably the best defense against poor uniformity. The more weathered the fibers, the weaker they become. During the ginning process these weakened fibers are broken, many into segments less that ˝ inch, thus lowering the uniformity ratio. Therefore, proper defoliation timing and expedient harvest are the best management techniques for optimum uniformity.

    Strength. Fiber strength is reported in grams of breaking load per tex. A tex is equal to the weight in grams of 1 kilometer of fiber. In essence, it is a measure of force required to break a bundle of fibers. Low strength cotton, less than 25.5, will incur discounts of at least 1 cent/lb.

    Fiber strength is also related to varieties and to weathering in the field. Therefore selecting a variety with higher strength and timely harvest will help to attain the maximum strength from a crop.

    Color grade. Color grade is now documented by HVI testing. It is determined by measuring the amount of yellowness and reflectance that a sample of fibers possesses. The base color grade is 41-4. As the number for color grade increases to 51-4 or 42-4, discounts are incurred based on length. In fact, a base length of 34 and a color of 51-4 will be deducted 3.8 cents/lb. At that same color grade a length of 33 would be discounted 5.85 cents/lb.

    Fiber color is directly related to weathering. A boll is at its optimum color grade the day it opens, after that color grade begins to decrease. Timely defoliation and harvest that prevents exposure to rainfall and prolonged high humidity is the best tactic for producing fibers of good color. Color grade is so closely related to the environment and weathering that it is also related to overall fiber quality.

    Replant Riddles. (Brown) The following article was submitted for publication on the website

    It was a cold, gray day in mid-April 1978. I was on the edge of a 200-acre field near Town Creek, Alabama, with an experienced but anxious cotton farmer. He asked me, the new county agent fresh from the university and still wet behind the ears, "Should I replant this patch? If I'm going to do something, I need to do it NOW! What do you think?" I flinched, clinched my jacket tighter, looked at the struggling, weak stand, and said hesitantly, "I'm not sure. Maybe you ought to wait." The weather stayed cold and wet, the decision became obvious, and he replanted.

    Replant decisions can make even seasoned growers and advisors doubt themselves. Such situations involve the frustrations of an unsatisfactory first attempt, added expense, and future uncertainties. There is stress. There is urgency.

    The logical starting point is to assess the existing stand in terms of plant number, skips, and general health. A viable plant every 12 to 15 inches is usually sufficient for normal yields. Stand uniformity is important. Fairly consistent stands that have at least 10,000 to 15,000 plants/A are often adequate, especially in environments with a long growing season. As numbers of skips greater than 25 or 30 inches increase, so does incentive to replant. Where earliness is critical, perhaps more plants are required and fewer skips can be tolerated.

    Besides counting plants, evaluating seedlings for health and vigor is also important. Roots and stems should be examined for lesions and darkened areas indicative of seedling diseases and for other abnormalities such as root pruning. Check stems, foliage, and bud tissues for mechanical and chemical injury. The former damage can be caused by insects, sand, wind, and hail; the latter by herbicides, insecticides, nematicides, and fertilizer. Keep in mind that any mechanical injury which cuts the stem off below the cotyledon node effectively kills the plant–there are no buds beneath that point to regenerate growth. Chemical injury on the cotyledons or first true leaf may be inconsequential IF new growth displays strong, healthy color. Despite early problems, the appearance of normal, vigorous roots, stems, and foliage give cause to believe that the plants have "turned the corner" and are on the road to recovery. With healthy roots and slick, green emerging leaves comes confidence to keep a stand with a reasonable density.

    Prevailing weather and the calendar must also be considered. A grower may keep a sparse, substandard stand if sustained dry weather casts doubt upon the likelihood of success the second time around. Irrigation makes these decisions easier. Tolerance for a marginal population should also grow as the date gets later. Replanting a questionable stand may be a reasonable choice in mid-May but unwise as it gets later and later.

    Should yield goal influence the decision? Generally, no. Research and experience indicate that a wide range of populations can make comparable yield. As stated earlier, even densities down to 10,000 lants/A are often adequate for normal yield.

    On this subject, I recall a replant question several years ago at a Georgia plantation that was producing cotton for the first time. The managers were under pressure to do a good job, to have things looking good, and to make big yields. They had planted strip till cotton in a deep furrow, had suffered some herbicide injury, had lost some stand, and were ready to start all over. While cotyledons were chlorotic, new leaves were showing signs of recovery. Independently, a consultant and I both urged them to keep what they had. Having already replanted some, they had a ready comparison. In the end all the fields made just over 1200 lb/A and were within 20 lb/A of one another.

    If counting and looking and scratching and thinking and thinking some more still leave the issue unsettled, apply the rule of thumb: WHEN IN DOUBT, DON'T REPLANT.

    There is one production system in which stand density is so critical that a shortage cannot be tolerated. In ultra narrow row cotton (row spacings of 10 inches or less), stand establishment is absolutely critical to weed control, canopy height control, crop maturity, and harvest-ability. If in doubt in UNR, plant some more seed!

    And if you replant, how should you proceed? There are many, many ways. Each field has to be handled according to the problems present. Often, the best approach is to do as little as possible, to replant on the existing bed or tilled strip with little or no soil disturbance. This is particularly true where soil moisture is limiting. Believe it or not, you can plant new seed right on top of existing plants, but of course, that creates the challenge of a stand of varying age. Conversely, if a stand has been lost to seedling disease, aggressive tillage and an in-furrow fungicide may be needed.

    If chemical injury has occurred, you must consider the persistence of the compound involved. Some products may have been sufficiently degraded, diluted, or dissipated so as not to pose a threat. Sometimes tillage is warranted. Sometimes a field must be abandoned.

    A couple of years ago, Glen Harris and I visited a field representing 600 acres in which young seedlings were chlorotic, burned, and withering. The farmer had overdosed almost two-fold the N in his starter fertilizer application. Even though it was nearly June and very dry, he had no choice but to re-till and replant.

    Tillage is the best means to destroy an old stand. Herbicides are less effective. Even non-selective products such as glyphosate and paraquat are erratic, especially if the crop has several true leaves, but of the two, paraquat is slightly more effective in suppressing or killing young seedlings. Remember, the many glyphosate products have essentially zero effect on RR cotton.

    Dual Magnum in Georgia Cotton. (Culpepper). Many questions have been raised regarding the use of Dual in Georgia cotton. Dual Magnum is labeled for use in Georgia cotton and can be applied to any cotton cultivar by topical or directed application when the cotton plant is between 3 and 12 inches tall.

    Dual Magnum applied postemergence (directed or topically) will not control existing weeds. However, residual control of pigweed, most annual grasses, yellow nutsedge, Florida pusley, and tropical spiderwort have been noted in research trials.

    With the expected 87% Roundup Ready cotton in Georgia during 2002, a tank mix label of glyphosate plus Dual Magnum applied topically when cotton is between 3 inches and the 4-leaf stage may be beneficial to growers. This application would likely provide both postemergence and residual weed control. HOWEVER, as of April 16, no published label allows this tank mixture and the Dual Magnum label actually states that when Dual Magnum is mixed with glyphosate the spray must not contact the leaves of Roundup Ready cotton. Syngenta is reportedly working on two labels allowing the mixture of Touchdown IQ plus Dual Magnum. This label will hopefully be available in the near future.

    With tank mixtures of glyphosate plus Dual Magnum applied to Roundup Ready cotton, one should expect pin-point speckles on all cotton leaves that were present at the time of the application. Over 20 trials in Georgia and North Carolina have shown that this speckling is temporary - crop maturity and yields are unaffected.


  • Do NOT apply Dual at planting (preemergence or preplant).
  • The Dual label clearly states to NOT use this product on sand or loamy sand soil.
  • The Dual label also states to NOT apply topically to cotton with any adjuvant or with fluid fertilizer.
  • Do NOT apply Dual within 5 days of a Staple application (do not mix Staple and Dual!!!!).
  • Selecting a Glyphosate Product to Apply Over-The-Top of Roundup Ready Cotton. (Culpepper). (Special thanks to Dr. Alan York of NC State University for help in preparation of this section.) There are at least 15 glyphosate products being sold in Georgia. In addition to the typical burndown and hooded sprayer uses of glyphosate, many of these products are labeled for over-the-top application to Roundup Ready cotton. Those products that are labeled and have caused little to no leaf speckling in University of Georgia or N. C. State University field trials are noted in the following list. Additional products will be evaluated during 2002.

  • DuPont Glyphosate
  • Glyphomax
  • Glyphomax Plus
  • Glyphosate Original
  • Glyfos X-TRA
  • Roundup Original
  • Roundup Ultra
  • Roundup UltraMax
  • Touchdown IQ
  • *All products were applied with their recommended adjuvant system. All products were applied over-the-top between cotton emergence and the four 4-leaf stage.

    Insect Scouting a MUST. (Roberts) Recent years have been difficult from a production and pricing standpoint. Although the 2001 crop renewed confidence in our ability to make a cotton crop, the price outlook continues to place a strain on operating budgets. Today more than ever, it is imperative that we achieve the highest possible return from each and every input. From an insect pest management perspective, achieving such returns begins with insect scouting. Insect management decisions are only as good as the information on which they are based. There are numerous well trained and experienced scouts and consultants in Georgia to fill this important need. Several cotton insect scouting schools will be held at various locations across the state during the upcoming weeks. These programs offer basic information on cotton insects and scouting procedures and will serve as a review for experienced scouts and producers and as an introduction to cotton insect monitoring for new scouts. See the UGA Cotton Calendar for a list of locations, dates and contacts.

    Hubbub about Glyphosate Formulations. (Brown) Considerable publicity has been generated in recent months regarding the suitability of certain glyphosate formulations for Roundup Ready cotton. The banter has included messages which imply "our product is better than their product" or which state flatly, "some products may seriously injury RR cotton."

    Regarding weed efficacy, most glyphosate products and formulations work quite well. Unquestionably, differences exist in adjuvant systems and these differences affect speed of activity, performance under stress conditions, and resistance to wash off. In terms of weed control, the most critical issues influencing glyphosate performance are product rate, weed size, and environmental conditions.

    Adjuvants and salts also influence the potential for foliar injury from glyphosate applications to RR cotton. While it is true that greenhouse studies have identified some concerns (i.e., visual injury to treated plants) with a couple of formulations, it is incorrect to implicate a majority of glyphosate products. Keep in mind that only certain products are approved for over-the-top application in RR cotton. In some cases this might be merely a regulatory, financial, or legal restraint rather than a biological one. However, the fact that a couple of new generic products may cause foliar burn to RR cotton under humid, rapid-growth conditions gives reason for Dr. Stanley Culpepper's advice, "Be careful with a glyphosate product with which we have zero experience. Spray a few rows and observe them, or better yet, let your neighbor spray his crop and then watch what happens." No doubt he will be evaluating a host of glyphosate products in the field this year.

    Generic versus Basic Manufacturer: Approach and Implications. (Brown) The following article appeared in the Georgia Cotton newsletter in March 1997. While some product and company names are now different, the basic ideas still apply--perhaps even more so in 2002: (1) Generic products provide pressure to keep pesticide costs low. (2) Name brand products from the basic international research/development companies provide economic capital to maintain existing products and develop new technology.

    With many pesticides, producers have the option of purchasing the "name brand" product or a similar generic product. Name brand/generic products (and active ingredient) available in cotton include Bladex / Cy-Pro (cyanazine); Bueno / MSMA (methane arsenate); Caparol / Cotton-Pro, Prometryn (prometryn); Cotoran / Meturon, Flo-Met (fluometuron); Karmex / Direx, Diuron (diuron); Orthene / Acephate (acephate); Prep / Super Boll, Ethephon, Pluck (ethephon); Thimet / Phorate (phorate); and Treflan / Trilin, Trifluralin, Trific (trifluralin).

    Generally speaking, the "name brand" products are discovered, developed, and marketed by basic manufacturers, companies such as AgrEvo, American Cyanamid, BASF, DowElanco, DuPont, FMC, ISK, Monsanto, Novartis (the company created by the merger of Ciba and Sandoz), Rhone-Poulenc, Rohm and Haas, Uniroyal, Valent, and Zeneca.

    There are many "generic" pesticide companies. Some merely formulate products, others produce and formulate their own active ingredients. Among the prominent generics in our area are Drexel, Griffin, and Micro Flo as well as those associated with major distributors, Clean Crop (UAP, Georgia Ag Chem), Riverside (Terra), and Setre (Helena).

    From initial discovery and registration with the U.S. Patent Office, a new product is patent-protected for 17 years. Unfortunately, all the tests necessary for pesticide registration--toxicology, environmental fate, efficacy, formulation, label development--may consume as much as 8 to 12 of those years and thus the company has reduced time to recoup its investment. The high costs of registration coupled with the limited exclusive life of a brand name product work to elevate the cost of new products. Cost of new pesticide registration now exceeds $50 million. Perhaps grower cost could be reduced if patent rights extended from the time of initial marketing.

    A generic product can enter the market once the patent expires for an active ingredient, BUT the generic company is obligated to reimburse the basic company for the cost of the data package which supports the registration. How much compensation is appropriate is almost always contested, and the matter is usually settled by litigation. The generic product label is virtually identical to the brand name product in use pattern and rate.

    Generic products provide an economical alternative for many "mature" products for which the patents have expired. Priced cheaper than related brand name products, generics create competition and hold down prices for traditional standard pesticides. Thus, the presence of generic producers in the marketplace has a moderating effect on costs, and farmers reap the benefits: less expensive pesticides.

    But there is another side of this issue. The research and development efforts of the basic companies provide the technology of the future. Sales of traditional products fuel the development of new products. Profits from existing products not only go towards research and development, but they also provide the funds to defend existing products in the regulatory arena, as in re-registration. In addition, there has traditionally been a significant presence of the basics in terms of product support for troubleshooting, resolving complaints, and industry good will. In other words, the basic manufacturer typically provides greater overall service to their products than most generic companies.

    What about the quality of generic formulations? Many are quite good, essentially equal if not superior in performance or utility to the brand name products. Some are not as good and create problems under marginal mixing conditions (low water temperatures, pH extremes, or poor agitation).

    Many of these same issues exist in the realm of pharmaceuticals.

    Both basics and generics offer important choices to the grower. The latter encourages economy in the system, the former provides undergirding support for the present and potential technological advantage for the future.

    Edited by: Philip H. Jost, Extension Agronomist-Cotton & Ag Crops

    Contributions by:

  • Steven M. Brown, Extension Agronomist-Cotton
  • Stanley Culpepper, Extension Agronomist-Weed Science
  • Philip H. Jost, Extension Agronomist-Cotton & Ag Crops
  • Phillip Roberts, Extension Entomologist-Cotton

  • Putting knowledge to work
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