August 19,2015 Cotton Report & Conditions
GENERAL CROP GROWTH AND CONDITIONS
The last week of July and early August provided slightly cooler temperatures and scattered rainfall to relieve heat/drought stress to plants. Thus, many areas retained bolls set on the upper portion of the plant that might have otherwise aborted. Regrettably, for some fields, the rains were too late since plants had essential ceased bloom. Even so, potential yield estimates are for above average crop yield. A boll count survey conducted during mid-July showed that even fields that had ceased bloom had 12-16 medium to large bolls per foot of row with the potential to set and/or retain another 3-5 bolls. Thus, even for these fields, 2 bales per acre yield potential is still possible.
Beyond early August, rains again ceased, so for most fields maintaining existing bolls will be key to high yield. Having thus said, additional bolls set between now and about August 20th-24th should develop into harvestable bolls. Whether or these bolls form to maturity or abort will depend upon rainfall and temperature between now and August 24th.
Plant Growth Regulator (mepiquat)
The primary goal of plant growth regulators is to encourage early plant maturity. Generally, to gain this advantage, products need to be applied a few weeks prior to bloom and again at bloom. When applied as such, these products also provide the benefit of smaller leaves and shorter internode length. This provides the benefit of slower growth, earlier maturity and allowing sunlight to the bottom portions of the plant to prevent potential boll rots.
Many plant growth regulator applications were not made this season due to extreme heat and drought conditions. Thus, with the return of scattered rainfall across the county, many producers are inquiring of the benefit of late season application of these products. The theory provided by growers for this late season application is that the products may provide for less plant growth (smaller plants) and thus easier defoliation when the time for defoliation arrives. Another concept is that the plant growth regulator will redirect the plant’s energy into boll development and thus result in less regrowth. Regrettably, neither of these theories is true. North Carolina State University has studied late season application of these products but no advantage has been realized for late season application of a plant growth regulator. Data and additional information on this topic is found HERE. Additionally, Dr. Keith Edmisten, NCSU Crop Science & Extension Cotton Specialist noted additional comments on the NCSU Cotton Facebook page HERE.
Having thus said, three are two conditions that may benefit from a late-season plant growth regulator application. The first is for fields that had excessive nitrogen (N) rates that have created a sudden uptake of N with retuning rainfall (especially after a drought). Excessive growth favors boll rot (due to excessive shades and moisture) and may attract late-season stinkbugs. If slowing plant growth and decreasing leaf size may protect bottom bolls from boll rots, it may be advantageous to make this application. The second situation where perhaps a late season plant growth regulator may be beneficial is for very late-planted cotton. Most of the late-planted cotton fields have been blooming for only a few weeks. Application may benefit these fields in terms of earlier maturity. However, even these theories are speculative. Any late-season plant growth application made with intent of a positive return on invest should be made caution.
Scouting fields composed of mostly large bolls should include monitoring for stinkbug damage. Remember that NCSU data reflects an economic threshold that varies according to the dominant boll size since all bolls are not equally susceptible to stinkbug damage. Thus, fields with a greater number of larger bolls than smaller bolls will have a much higher threshold. Thresholds for stinkbug and scouting tips is found HERE. Note that the specie of stinkbugs is critical in pesticide product selection so proper identification is critical. Also, while not identified as a common pest within this area, the Marmorated Stinkbug has become a significant pest in some areas within NC. This pest has a greater ability to injury large bolls thus should be monitored throughout the season.
Due to the extended period of extremely hot and dry conditions, monitoring for spider mites may also be warranted. Spider mite population in fields is still low, but common in cotton and peanuts. Thus, the populations may increase in isolated areas. Whether or not a treatment is warranted should reflect the boll maturity, weather circumstances (rainfall normally greatly reduces spider mite population) and level of spider mites present. Too, potential yield of the field will need to be evaluated simply because adequate control of spider mites usually requires two sequential treatments of an expensive product. Given the low cotton price, if bolls are mature and beginning to open, it may not be economically justified to make a mitiicide application.
August is not typically when growers in this area defoliate cotton. However, given the seasonal variances, several key points need to be considered. First some fields have cut-out. These plants have a compact fruit set, no flowers and reddening leaves. Many of the bolls are mature with the remaining bolls likely to be mature enough for defoliation within the next 10-14 days. These particular fields will yiled highest soon after bolls open. Delay of harvest will lead to potential yield loss. Many of these fields have good yield potential with 12-18 bolls per foot of row. Thus, it is logical to defoliate these fields as soon as possible for harvest.
Another consideration for all fields is that typically, drought stressed cotton has thicker leaves that do not readily absorb defoliate materials. Three means of compensation for this situation have been to tank mix both hormonal and herbicidal products in the application, increase product rates slightly, and/or add a silicone/MSO type surfactant. Some state have data supporting utilization of crop oil and/or ammonium sulfate materials but these products are also more likely to desiccate leaves. Thus, NCSU does not recommend these particular practices. (Historically, inclusion of both hormonal and herbicidal products applied at appropriate rates for a given temperature with silicone/MSA surfactants has proven to work well.)
Consideration of potential regrowth, especially on severely drought stressed cotton, should also be a concern. Typically, if fields cut out early, terminal regrowth occurs rapidly after rainfall occurs. July through September months normally provide the greatest monthly rainfall for this area yet temperatures are likely to remain high enough to favor plant growth. Since cotton is a perennial plant, regrowth may occur rapidly. Thus, inclusion of a product such as Dropp, Freefall or Ginstar that controls regrowth is advisable. Should this regrowth occurs prior to defoliation, selection of products that are better defoliants of juvenile growth such as those listed in the chart below are advised.
Timing of defoliants is more difficult to recommend. Generally, a foolproof method is to use the Nodes Above Cracked Boll (NACB) method. Using this method involves finding the highest first position boll that is cracked enough to show lint and count the number of harvestable, first position bolls on the nodes above this position. When NACB is four or less, it is generally safe to defoliate. The potential problem with this method is that this rule may not apply to fields with a low plant population. Too, in many cases, fields could be defoliated earlier, depending upon weather and how quickly the bolls were set during the summer growing months. Thus, a better method for those wishing to maximize favorable harvest weather conditions and yield is to check seed maturity. Simply cut bolls open and slice seeds within the lint. Immature seeds are white and milky (jelly-like) in appearance. As seed coats begin to turn brown and the kernel of the seed fills the seed cavity (no jelly or milky substance), it is generally safe to apply harvest aids. When the last harvestable boll has mature seed coats, defoliant can usually be applied safely.
Consideration of timing of defoliant materials should also consider historical weather patterns and the projected weather forecast 3-5 days after application. In regards to historical weather, late August through about mid-September usually provide best weather circumstances for defoliation within this area. Afterward, rains and cooler weather prohibit application or make decisions more difficult and expensive. Thus, early defoliation is favored. Additionally, one must evaluate forecast immediately after application. Sunny weather following application usually results in better product performance compared to overcast, cloudy weather following the application. This holds true even is temperatures are warmer during the cloudy/overcast days.
Lastly, tropical storm systems must be considered. Some producers have applied defoliant materials 3-4 days prior arrival of a tropical storm system with excellent results. Crops are generally defoliated and ready for harvest about the same time as soils drain to levels acceptable for travel by harvest equipment. Others growers prefer to have fields entirely defoliated prior arrival of the tropical storm assuming that less leaf area will result in less plant lodging and easier harvest. However, in most cases, we simply do not have much of a choice simply because the tropical storm system arrives prior to the crop being mature enough to apply defoliant materials. The point is that a tropical storm system will normally cause yield loss regardless of the defoliation strategy chosen. Very little data is available to provide information as to which strategy is best. Thus, make the decision to defoliate or not defoliate with an approaching tropical storm system based upon crop maturity, cotton picker accessibility and other management priorities.
Further information and suggested defoliation rates based upon temperature, plant growth and boll maturity is found HERE
To download the chapter on defoliation from the 2015 Cotton Information publication, click HERE
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