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PGR requirements and benefits for 2021 dryland and irrigated cotton

Brad Haire brad-haire-farm-progress-july-cotton-GA-6-a.jpg
Cotton PGR application decisions are complex. Many factors contribute to the decision when to initiate applications and what rate to use.

The vast majority of the cotton crop in Georgia is squaring, sidedress nitrogen applications are going out. With recent rains across Georgia much of the crop is actively growing. Now is the time to start thinking about PGR applications.

PGR application decisions are complex, and many factors contribute to the decision on when to initiate applications and what rate to use. Below are factors to consider when thinking about PGR strategies:

  • Variety Selection - Some varieties are more aggressively growing than others. Varieties similar to NG 4936 B3XF or PHY 400 W3FE show good response to PGRs (i.e. they need less growth management), whereas varieties like DP 1646 B2XF or NG 5711 B3XF are less responsive, and may require more intense growth management.
  • Yield Goal - In Georgia, we still recommend nitrogen fertility based on yield goal. Based on the nitrogen fertility and the yield goal of certain fields, some may require more intense growth management than others, particularly the high yield environments with high amounts of nitrogen and irrigated production. These high productivity fields will likely require heavier growth management. Dr. Glen Harris and myself are working on a study together this year to help illustrate this point, and hopefully we will have some valuable data to share with growers across the state this winter.
  • Pest management program - Although PGRs don’t help manage pests, I believe they should be incorporated into an overall pest management system. Dr. Bob Kemerait tells me that timely PGR applications can assist in target spot management by reducing rank growth and improving airflow through the crop canopy. He also tells me Australian black licorice from Buccee’s is pretty good. I’ll take his word for it.

PGR’s can also be incorporated into an insect management program. The two main pests that will cause cotton to drop squares or flowers would be tarnished plant bugs or caterpillar pests. In a situation where plants are losing squares/flowers due to insects, this issue should first be corrected by managing those problematic insects. Then, a timely PGR application could assist in retaining squares or flowers in other positions, thus compensating for the previous loss.

In terms of weed management, caution should be taken when tank-mixing PGRs with certain herbicides. Although our current varieties have incredible tolerance to Roundup, Liberty, and either 2,4-D or dicamba, some people still prefer to use products such as Staple or Envoke. These products tend to slow cotton growth, and if tank-mixed with a PGR this effect would only be compounded.

In terms of initiating PGR applications, this decision is much easier in irrigated production systems. With aggressive varieties in high yield environments or in fields with a history of rank growth, PGR applications should be considered prior to bloom. In most dryland scenarios, at or just prior to bloom is a good time to consider making a PGR application. In both situations, follow-up applications should be decided by looking at the length of the fourth internode from the top of the plant. This is the “go-to” measure as this node is fully elongated, meaning it is a good indicator of the growing conditions and vigor of the crop. As a general rule, if the fourth internode length is greater than 2 to 3 inches, a PGR application may be necessary. A simpler way to evaluate this is to determine if three or more fingers can fit in the fourth internode. Pictured below is an example where more than three fingers could fit in the fourth internode, indicating that a PGR application might be necessary. 

Dryland scenarios can be a little more tricky, as an untimely application prior to a dry spell or at a time when the crop is stressed can result in stunting and reduced yield potential. Therefore, weather becomes a bigger factor when making decisions on PGRs for dryland cotton and long range forecasts should be consulted. Additionally, lower rates should be considered in dryland production compared to irrigated.

There are numerous products that can be utilized by cotton growers for PGR management. Some of those products, use rates, and restrictions can be found here.

Keep in mind that the sum of all mepiquat chloride containing products must not exceed 0.132 lbs of active ingredient of mepiquat chloride per acre per year. This is equivalent to 48 oz per acre per year of Pix.

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