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Set and protect crop in late-planted cotton fields

Tennessee's cotton crop has gotten off to another rocky start and has many farmers wondering what to do next. Traditionally, cotton planting in Tennessee starts near the end of April and continues until mid-May, with the bulk of the cotton planted during the first and second weeks of May.

Producers have been forced to plant outside these recognized windows in recent years. Although Tennessee has been spoiled with longer-than-normal growing seasons and higher-than-average DD-60 accumulation, long-term data tells us that in 50 percent of the last 30 years, a killing freeze occurred during the second and third weeks of October.

Fortunately, growers have earlier-maturing varieties, Bt cotton for worm control, and boll weevil eradication in their arsenals to allow for a potentially longer season. Tennessee cotton, however, is grown on the northern edge of the Cotton Belt, and growers have not seen an early fall freeze in the last few years.

Late-planted cotton still has the chance to be productive, but making a good crop will require intensive management and some luck. It is imperative to manage for an early, once-over harvest.

Earliness is generally a product of variety, planting date, sound fertility practices, favorable early-season temperatures, first fruiting node, fruit retention, plant growth regulation, and environmental factors leading up to maturity.

Several of these are out of our hands, but there are things we can do to achieve earliness. At this point, attention should be focused on setting and protecting the crop that we can harvest. To maintain earliness, here are a few management guidelines.

Match soil type with the correct nitrogen rate. Bottom soils and productive hills that tend to produce large, rank cotton should be fertilized accordingly. Excessive nitrogen rates promote rank growth and delay maturity. Tennessee currently recommends 30 to 60 pounds total nitrogen for bottom soils and 60 to 80 pounds total nitrogen for upland soils. Avoid late applications of nitrogen and match rates to realistic yield potentials. On most soils, yields are not increased by applying more than 80 pounds of nitrogen per acre, but maturity may be delayed.

Always follow the glyphosate label for overtop applications of glyphosate. The last overtop glyphosate application should be made at the fourth true leaf (node) stage of development (until the fifth true leaf reaches the size of a quarter). Directed applications of glyphosate and other materials should be directed towards the base of the cotton plant with care taken to minimize contact of the spray with cotton leaves. Late overtop applications and sloppy post-directed applications may result in boll loss, delayed maturity and/or yield loss.

Fruit retention is the foundation for eliminating the potential for rank growth and preparing the crop for an early harvest. Maintaining early-season fruit retention above 80 percent will suppress excessive vegetative growth and increase the potential for an early crop. In a year like this, the two most important things are to set and protect the crop you have now and hope Mother Nature cooperates this fall.

Late-planted cotton often grows more vigorously than an early-planted crop, so growers need a proactive rather than reactive approach to plant growth regulator applications. It is much easier to control cotton growth when plants are smaller with lower application rates than with higher rates when plants have become rank.

Shutting down a vigorous plant is difficult at best and usually expensive. Most growers know which fields or portions of fields can become rank if conditions are right.

Lower-rate, multiple applications often give good results and are usually safer on many of these soils because of the reduced risk of stopping vegetative growth in the event of drought conditions. However, low rates are useless on larger cotton that has already become rank. Match the correct rate with the situation at hand; larger cotton will need higher rates.

It is difficult to make a PGR recommendation that will cover the needs of all fields and for that reason it is important to find a program tailored to the individual field.

Don't chase phantom bolls, especially on a late-planted crop. Defoliation should be timed with harvest of the mature bolls in mind. Although a once-over harvest is desirable for a number of reasons, growers should consider a second picking on late-planted cotton to decrease weathering and poor harvest conditions for the most-profitable bolls.

Bolls set late in the year in the upper portion of the canopy will not likely contribute to yield. Addition of an ethephon-based boll opener will increase the percent of the crop picked at first harvest. Ethephon does not, however, promote crop maturity and no amount of ethephon will open small, immature bolls. Ethephon products need at least 50 DD-60s to work and higher rates will be needed under cool temperatures.

Chism Craig is the Extension cotton and small grains specialist with the University of Tennessee.

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