Production Ideas for 15-Inch Cotton
Research was conducted during the 2004 growing season in North Carolina trying to identify the pros and cons of 15-inch cotton production. Obviously, the studies will be replicated over the 2005 growing season and beyond to incorporate the “good” and “bad” years. Last years growing season was outstanding with respect to cotton growth and development. There was a near “perfect” amount of heat-units and rainfall to push the yield potential of cotton grown in North Carolina. As most of you know, environmental conditions fluctuate from year to year, and not every growing season is conducive for a high-yielding crop. With that said, the data from 2004 can give insight on what the “potential” is for 15-inch cotton. We also looked at 15-inch cotton for two previous years, however it was harvested with a broadcast “finger” type stripper.
Planting considerations and variety selection
Seeding rates
High seeding rates (>100,000 seed/Ac) have typically been used in UNR cotton. The reason for such high seeding rates was due to the harvesting method. The broadcast finger strippers are not very efficient when cotton plants have vegetative limbs on them. There are two reasons for this; (1) vegetative branches are on the bottom of the plant and the fingers tend to grab them and pull the whole plant up out of the ground and (2) there is a lot of bark associated with those branches that the bur-extractor can’t separate from the seed cotton. Thus, high plant populations allows for compact plants with short sympodial branches and no vegetative branches, which is conducive for stripping efficiency. With the PRO-12 VRS row units, those high seeding rates are not needed. You can tolerate some vegetative growth because you are spindle-picking. Thus, with high seed costs and tech fees associated with transgenic varieties, if high plant populations are not an agronomic necessity, then from an input cost perspective lowering seeding rates without sacrificing yield and quality is of the utmost importance.
Our data shows that plant populations ranging from 25,000 to 75,000 plants/A are optimal, both economically and agronomically, with respect to fruit load and position on plant. There are no population effects on plant height, however when you get above 50,000 plants/A there is a reduction in the number of main-stem nodes (2 to 4 nodes less). Higher plant populations yield more seed cotton weight on the bottom of the plant on a per acre basis (due to the high number of plants in an acre contributing), but they do not offer as much as the lower populations on the middle and upper portions of the plant. By choosing a seeding rate higher than 75,000 plants/A the ability to make a “top crop” is severely limited. The best insurance is to spread your seed cotton weight out, up and down the plant. This is because one can never predict what the weather is going to do over the course of the growing season. There are no differences in lint yield when populations are above 25,000 plants/A, however anything below that may result in reduced yield. Fiber quality is the same across populations, but the lower plant populations tend to yield a slightly longer staple length.
Based on the accumulated data, the recommended seeding rate is the same as it is in wide-row production. There are 34,848 linear row feet in an acre on 15-inch rows, compared to 13,756 linear row feet on 38-inch rows. So, 1.5 seed/ft on 15-inch rows will yield 52,272 seed/A, and assuming 85% germination that will leave a final plant population of ~ 44,000 plants/A. This appears to be the optimum population to achieve when planting on 15-inch rows.
If wet field conditions or other constraints prevent planting until late May or around the first of June, then increase your seeding rate up towards the 75,000 seed/A mark. This will give the plants a bit of earliness due to the fact that there will be less bolls per plant, but the number of plants in an acre will offset the reduction in boll number and overall lint yield can be the same.
Variety selection
As with wide-row production, 15-inch cotton production relies heavily on planting elite varieties with high yield potential coupled with an exceptional fiber quality package. Preliminary research has shown that 15-inch cotton does not require a “special” variety for production. In 15-inch cotton you are keeping the plant population the same as in wide-row production, it is just that in 15-inch cotton all you are doing is “squaring the plants out” over the field. So, as a result, the same varieties used in wide-row production will work excellently in 15-inch cotton. Your state’s OVT results are a good place to identify a variety for planting to a 15-inch row configuration. A protocol for a 15-inch cotton OVT has been put together for the 2005 growing season, and more details will be known at a later date regarding variety selection. Data regarding varieties from last year’s trials have been included.
| Lint Yield (lbs/A) | Fiber Quality2 | ||||||
| Variety | Row Spacing | Ginout | Mic3 | UHM | Strength | UI | |
| 15" | 38" | % | inches | g/tex | % | ||
| ST 5599 BR | 1307 a | 1173 b | 41.3 | 4.94 | 1.08 | 29.2 | 82.6 |
| ST 5242 BR | 1452 a | 1191 b | 44.9 | 4.97 | 1.10 | 29 | 84 |
1. Means followed by the same letter are not significantly at the 5% level, and are compared across row spacing within variety.
2. There were no differences among row spacings with respect to fiber quality, thus data were averaged over all treatments.
3. High Mic values are due to inclement weather (two hurricanes) that prevented timely harvest.
The figure above illustrates the possibility of extending the planting period with 15-inch planting. Notice that the 15-inch (the red bar) greatly yields more than conventional 36-inch rows (blue bar) for the May 25th planting date.
Weed Control
Weed Management in 15-inch cotton is more difficult than in wide-rows because there are fewer control options (i.e., no postemergence–directed herbicides and no cultivation). A uniform stand is critical in 15-inch cotton weed management because much of the mid-season control comes from canopy closure (shading of the weeds).
Only Roundup Ready or Liberty Link varieties are suggested for 15-inch cotton. In 15-inch Roundup Ready cotton, a preemergence application of Cotoran is suggested, especially if more than a light infestation of morningglory is expected. An addition of Prowl 3.3EC or Prowl H2O with Cotoran can broaden the control spectrum and pick-up species like annual grasses and pigweeds.
If no preemergence herbicide is used then two applications of glyphosate at the 1- to 2-leaf and the 4-leaf stage will be needed for broad spectrum control of weeds. If a preemergence application of Prowl plus Cotoran is applied then only one application of glyphosate is needed and should be applied at the 4-leaf stage. There are several tank-mix options with glyphosate being applied at the 4-leaf stage. A tank-mix of glyphosate plus Dual Magnum can provide residual control of annual grasses and pigweeds, while a tank-mix of glyphosate plus Staple can also be used. Envoke can be applied to 5-leaf cotton or larger to control morningglory, sicklepod, and pigweed species. Recent research conducted here at North Carolina State University has not seen a benefit of using Envoke if the aforementioned herbicide application strategies have been used correctly.
In 15-inch Liberty Link cotton, Prowl or Prowl plus Cotoran applied preemergence is suggested to aid in control of annual grasses and pigweed species. Follow with two over-the-top applications of Ignite. Base timing on weed size rather than cotton size. However, a second application needs to be made while the cotton is small enough to allow coverage on weeds under the crop canopy. Either Staple or Dual can be mixed with Ignite.
Growth Regulator Use
Previous research conducted showed that there were no differences in plant height in 15-inch cotton where we applied mepiquat chloride and where we didn’t, although we got a reduction in main-stem nodes where we did apply mepiquat chloride. The fields our trials were conducted in were not historically conducive for “rank” plant growth. There were no differences in fruit retention observed between treatments. Monitor your fields carefully and pay close attention to plant heights and internode lengths, and if they are out-of-line, then follow your states current guidelines for mepiquat chloride use.
Fertility
Follow soil tests guidelines with respect to pH, potassium, and phosphorus. If soil tests call for applications of these elements then they should be put out preplant. For nitrogen fertilization, we used 80 lbs/A of total N coming from ammonium nitrate, but ammonium sulfate will work just as well. The nitrogen containing fertilizer was broadcast spread. We chose ammonium nitrate for various reasons, and volatility concerns were the biggest reason. We do not have any evidence that nitrogen rates should be different than conventional cotton.
Insect Management
An In-furrow application of Temik is not possible due to label constraints. The formulation of Temik is not concentrated enough on a granule per granule basis to allow using it. Remember that there are more linear row feet in an acre on 15-inch rows than on 38-inch rows, and to get the proper amount of Temik out you will actually be applying 2.4 times more in 15-inch cotton. This is off-label. Seed treatments of Gaucho or Cruiser are another option for thrips control. Research here in North Carolina has shown that when using these seed treatments you get about 3 weeks of residual activity from these products, and as a result a foliar application of Orthene or Bidrin might be needed as a supplement (this is dependent upon thrips pressure). Obviously, the management guidelines for other insects such as plant bugs, stink bugs, and bollworms should be similar to wide-row cotton production.
