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Deltapine® cotton varieties may each respond a little differently to the application of mepiquat. The projected response of each variety is provided in Table 1. Cotton varieties listed as “very responsive” show the most response to mepiquat, meaning lower rates or fewer applications may be needed. Those categorized as “least responsive” to mepiquat may require timely early-season applications at higher rates or multiple applications to control vegetative growth.
When deciding to apply an application of Pix®, the actively-growing top five internodes of the cotton plant should be evaluated.1 Mepiquat chloride rate and timing sticks are available to provide recommendations according to the average internode length of the top five nodes of the plant.
Another way to determine application rate is to monitor the height and internode distance between the 4th and 5th node below the terminal node.
Mepiquat application rate recommendations are often based on the internode distance between the 4th and 5th node and the total mainstem node number. The longer the internode length, the higher the recommended Pix rate. Other plant measurements and field conditions can help assess the need for cotton plant growth control measures. Table 2 provides suggestions for growth control measures.
Mepiquat and other PGRs should be considered management tools used to maintain ideal cotton height and fruiting retention. In-season cotton-plant monitoring, provides the best information to determine application rate and timing of growth control measures. Every cotton field is under different conditions so growth management strategies should be tailored to each field situation.
Sources: 1Jost, P., Whitaker, J., Brown, S., and Bednarz, C. Use of plant growth regulators as a management tool in cotton. The University of Georgia Cooperative Extension. http://www.caes.uga.edu/. 2012 Research Summary: Effect of PGR strategies in cotton. The Learning Center at Scott, MS. Web sources verified 05/28/2018. 180602140625