Georgia Cotton: PGR Use and Reducing Stress in Late Planted Crops

Photo: Larry Stalcup, AgFax Southwest Cotton

The 2018 Georgia cotton crop is extremely variable in maturity. Much of the state has had cotton blooming and setting fruit for weeks where as other parts of the state still has a large portion of the crop yet to bloom. There is no one size fits all approach to management of this crop and decisions should be made accordingly.

With much of our crop planted late due to the rainfall in late May and June, we must remember that the window for blooms to become harvestable bolls is compressed compared to a full season crop. It is important during that early bloom period to minimize stress to the crop in order to retain as much lower node fruit as possible as the cotton does not have time to compensate for losses early on.

Remember that the best way to manage vegetative growth is by having high early season fruit retention. This limits the amount of available carbohydrates that the plant can use towards vegetative growth later in the season. PGRs should also be used to limit vegetative growth and enhance lower node retention.

When should we terminate our PGR applications? Research conducted at UGA and other parts of the country suggest that PGR applications should cease when cotton reaches 5 nodes above white flower. In theory a late season mepiquat application could stop further vegetative growth and divert carbohydrates and resources to boll production, but research has shown that there is no benefit to cotton yields, plant heights, fiber quality, or regrowth potential after defoliation.

One more note on PGRs, with the widespread rain across the state, the issue of rainfastness has been a concern when applying mepiquat. The rain free period after mepiquat chloride application is 8 hours. Although tank mixtures with an adjuvant are not necessary, their use may aid in plant uptake and help shorten that rain free window. Another option is Pentia (mepiquat pentaborate). Pentia requires a rain free period of two hours after application and that can be reduced to one hour when Pentia is tank mixed with an adjuvant.  

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If irrigation water is available, all steps should be taken to ensure that the crop does not encounter drought stress when adequate rainfall has not occurred. This is especially true for the first six weeks following first bloom as this is the period of peak water demand.

Irrigation scheduling has been a topic of conversation and research for the past few years and several quality cotton irrigation scheduling methods exist which use soil moisture sensor technology. However, if a grower does not intend to utilize one of these methods they are encouraged to follow the UGA Checkbook irrigation schedule which can be found on page 132 of the 2018 UGA Cotton Production Guide.

One thing to note when using this method is that rainfall or irrigation amounts do not “carry over” to the next week. For example, if water demand for a particular week was 2’’/week and you receive 3”, that extra inch does not affect the amount of water required for the following week.


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