To Pix, or not to Pix?

By Camp Hand

This year has been a unique one across the cotton belt, and Georgia has not been immune to that. The planting season was drawn out, and tough for many people. Georgia growers faced a number of challenges from being too cool and wet early, to too hot and dry in mid-May, and then too wet again to finish it out. Luckily I have not heard a lot about replant issues, and from what I am hearing and seeing as I travel the state our crop looks really good so far. The latest USDA crop progress report states that about 35% of our crop is squaring, which is great considering that most of our crop is late.

Now that much of the crop in Georgia is squaring, sidedress nitrogen applications are on the horizon, 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.

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.