Cut Out Application of Pix
The dry weather has a lot of people wondering if mepiquat chloride applications could prevent regrowth to maximize development of the bolls on the plant and to prevent regrowth.
Many people want to put mepiquat (Pix) on cotton now. There seems to be this idea that if you apply mepiquat the plant will not go into a “vegetative mode” and will then keep and fill the bolls it has and produce little regrowth.
1. Mepiquat does not change the “mode” of a plant. Cotton starts producing fruiting branches usually somewhere between node 4 and 8. Earlier varieties start this process lower, say nodes 4 or 5 while later varieties start the process later (higher on the plant) around nodes 6, 7 or 8. Once the plant begins to put on fruiting branches it will continue to put on fruiting branches from then on (with few intermittent exceptions that may occur on the lower part of the plant around node 7 through 10 where the plant reverts and makes a vegetative branch or two and then returns to producing fruiting branches). Once fruiting is well established the plant will only revert to producing vegetative branches if the terminal is lost. I have never seen any amount of any growth regulator change this process
Mepiquat applied earlier in the season appears to make cotton earlier in some instances by deducing leaf area and increasing the penetration of sunlight into the lower canopy. This tends to increase retention at the lower fruiting nodes. Late applications have very little chance of increasing sunlight penetration to leaves feeding harvestable bolls.
After a dry period, the plant has already decided which fruit it will keep and which it will abscise. I have not seen growth regulators like mepiquat affect this process either. If the plant has resources (water, N, P, K, carbohydrates etc), it will first use those resources for the bolls it has decided to keep. Regrowth is not at the expense of the development of those bolls but is driven by any extra resources the plant has available. Figure 1 shows that we saw no increase in resources allocated to lint following 16 oz of mepiquat applied per acre in 2007 and 2008.
Figure 1. The influence of cut-out applications of 16 ounces of mepiquat per acre on cotton lint yields in 2007 and 2008.
Figure 2. Grams of regrowth (dry weight) 21 days after treatment per 60 foot of row.
Figure 3. The influence of cut-out applications of 16 ounces of mepiquat per acre on percent defoliation 14 days after treatment in 2007 and 2008.
Summary: We have no data that supports the use of any form of mepiquat applied at cut-out to promote fruit development, prevent regrowth or improve defoliation.