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PGR Considerations

This article by our new Cotton Agronomist, Camp Hand, should help you out when making decisions on PGR applications. With the current weather conditions and state of the crop even dryland fields are in need of plant growth regulators.

Now that the vast majority of the crop in Georgia is squaring, sidedress nitrogen applications are going out, and 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 some of the factors to consider when thinking about PGR strategies:

  1. 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.
  2. Yield goal/Fertility and irrigation: 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.
  3. 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. And lastly, 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 in Table 1. Please 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.

Table 1. Plant growth regulator products, rates, and restrictions.

Growth RegulatorBroadcast rate/acreREI/PHIRemarks
mepiquat chloride* Pix 0.35L, others8 to 24 fluid
ounces
12 hrs/30 dDo not use more than 48 fluid ounces per acre per year. Increased rates necessary for more vigorous growth conditions, and for applications made
later in the season.
mepiquat pentaborate*
Pentia 0.82L, others
8 to 24 fluid
ounces
12 hrs/30 dDo not use more than 48 fluid ounces per acre per year. Do not apply to cotton that is drought stressed. Do not plant another crop within 75 d of last treatment. Do not graze or feed cotton
forage to livestock.
mepiquat chloride + kinetin*
Gin Out 0.35L, others
4 to 16 fluid ounces12 hrs/30 dDo not use more than 48 fluid ounces per acre per year. Do not apply to cotton that is stressed. Do not plant another crop within 75 d of last treatment. Do not graze or feed cotton
forage to livestock.
cyclanilide + mepiquat chloride Stance 0.92L2 to 4 fluid ounces24 hrs/30 dDo not use more than 22 fluid ounces per acre per year. Allow a minimum of 7 days between applications. Increased rates may be necessary for more vigorous growth conditions.
*The sum of all mepiquat chloride containing products must not exceed 0.132 lbs ai of mepiquat
chloride per acre per season.

In terms of what I have been hearing across the state and getting questions about, many of the recommendations I have been giving range between 6 to 12 ounces per acre. However, there are always the occasional, “I’ve got cotton up to my shoulder and haven’t sprayed a PGR yet.” To which I said, the maximum labeled rate for a single application is 24 ounces per acre. With much of the crop flowering and setting fruit it is time to start thinking about higher rates where growth is vigorous.

One final note I would like to stress is timeliness. If I learned one thing in my time working for Dr. Culpepper, it was that in a weed management program, regardless of crop or herbicides used, being timely is the biggest factor in being successful. We always stress timeliness with weed, insect, and disease management, and I think we should do the same with PGR applications. I believe that being timely and getting a “head start” on growth management will benefit us at the end of the season.

All of this is to say that these decisions can be complex. Luckily there are resources at your disposal to assist in these decisions – your local UGA county agent and specialists are here to help. If you have questions on PGR decisions, or any other aspect of cotton production, please contact your local UGA county extension agent and they will find you the answers you need.