Pix problems in northeast Louisiana cotton

BATON ROUGE, La. -- Cotton plants are abnormally short and blooming high in a number of fields in northeast Louisiana.

On many plants, there are 12 to 18 nodes stacked with 14 to 18 inches of mainstem growth. The plants are threatening cutout in some fields (nodes above white flower = 5), with average nodes above white flower between 6 and 8.

Some plants have set six to eight bolls, the largest being over quarter size. Vegetative growth has nearly ceased, and plants are putting most of their resources into reproductive growth prematurely. It is hoped vegetative growth will resume shortly and allow for a second set of bolls to be set late in the season.

The result is plants that contain a large fruiting gap, confounding late-season management.

This predicament is likely a result of the combination of Pix (the term Pix here is used to refer to all commercially available mepiquat-containing compounds) applications and cool, wet spring conditions retarding plant growth.

In many fields, Pix was applied very early to varieties that have a tendency to be growthy (example: DP 555 BR) based on recommendations that use a developmental stage rather than measurements of plant vigor. Applying Pix based on a stage of development (example: pinhead square) is not an appropriate means of timing applications because the plant vigor may vary across fields.

Use of Pix can result in reduced yields, especially when environmental stress follows. Before applying Pix, variety, soil type, fertility, irrigation potential, and field history must be taken into consideration.

With the diverse soil types found in Louisiana, one recommendation will not work with all soils. With increased plantings of growthy, late-maturing varieties, timing Pix application has been challenging to say the least.

Most recommendations have called for aggressive, early applications. This may be pertinent on some soils, but certainly not all. Only the most fertile soils in Louisiana with a history of producing tall stalks will benefit from these aggressive approaches.

The recommendations were generated on highly fertile, well-drained soils. They pertain only to a handful of our silt loam soils in Louisiana. They will not be pertinent on most soils in Louisiana.

This year, cool weather combined with consistent waterlogging on clay soils has restricted root growth and thus retarded plant development. Adding aggressive Pix applications has compounded problems on clay soils, resulting in stunted plants threatening to cut out prematurely.

Highly aggressive Pix applications on droughty, ridge-type soils are seldom warranted because of water stress potential, regardless of variety.

What to do?

If you are experiencing this situation, you should first stop applying Pix.

Second, do not apply fertilizer unless you are certain it is needed. Many fields have received fertilizer rates that will be ample despite losses caused by denitrification. Adding nitrogen will likely cause the plant to spike too rapidly when you receive a rain and leave you Pix applications again in mid- to late July.

If you feel strongly that nitrogen is needed, apply it. If you are unsure, it may be beneficial to take tissue samples to test nitrate levels. Very little research has shown a yield response to midseason foliar feeding. If your crop is on irrigated land, irrigate early if needed (next week in some cases).

Let the crop grow and monitor its progress. Cotton is a resilient crop and there is plenty of season left for it to set bolls. Your objective should be to gradually shift the crop from an almost completely reproductive phase back into a phase where the cotton develops vegetatively and reproductively simultaneously.

Be patient; the plants should slowly accumulate bolls throughout the season. This will reduce the disparity among the harvestable bolls. Some of the earliest bolls set may be lost in the process, but they would likely be lost anyway from trying to manage for late-season bolls.

For now, let Mother Nature determine the rate of development. This is especially pertinent to late-maturing varieties that have the potential to put on significant yields later in the season.

Use plant vigor measurements as guides to aid in any subsequent Pix application decisions. Following are some general guidelines for determining the need for Pix.

Typical measurements used to determine plant vigor include plant height and internode length. Several states recommend counting down the plant from the highest mainstem leaf (>quarter size) to the fourth leaf. Examine the internode above and below the fourth leaf and measure the larger of the two. This is a good indicator of the plant vigor over that past week or so. Long internodes will range between 2.5 to 3 inches while short internodes will be below 2 inches.

These are general guidelines and plant height should also be taken into account. Plant heights need to be in excess of 20 inches before considering Pix applications this time of year.

I cannot stress enough that the need to apply Pix applications must be examined on an individual field basis. Following blanket recommendations based on stage of development rather than crop vigor is simply "rolling the dice."

Joel Faircloth is the LSU AgCenter cotton specialist. e-mail: [email protected]

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