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The MEPRT Method to Determine Time and Rate of Mepiquat Chloride Applications: Uses and Misuses

J. A. Landivar


The use of the MEPRT stick and software has increased considerably during the last two years. The objective of the MEPRT system is to determine the time and rate of mepiquat chloride (MC) applications based on well-defined parameters that can be readily measured under field conditions. The system is made-up of two components: (1) The MEPRT stick used to determine the time of application and (2) the MEPRT software used to determine the rate of application. The MEPRT stick measures average length of the uppermost five internodes (ALT5). Since ALT5 is related to potential plant growth rate, this measurement is used to determine the time for MC applications. The technique was designed for use during the time of square initiation until the onset of carbohydrate stresses induced by the developing fruit load. Best results are obtained when the stick is used from matchhead square stage (approximately 40 days after emergence) until two weeks after the appearance of the first bloom. Using this technique outside this range requires a different interpretation of the results than that given by Landivar et al., 1995. The MEPRT software estimates the rate of application by estimating the amount of product needed to increase the concentration of MC in the plant to a pre-determined level. The program accomplished this by estimating plant weight with a regression model that uses plant density, number of mainstem nodes and plant height as independent variables. A strong correlation between plant height and weight exist during vegetative development. As the fruit load develops, the relationship between plant height and weight becomes insignificant. In mature plants (after cutout) this relationship is non-existent. Since the estimation of plant weight is essential for the calculation of the rate of application, we recommend the use of the MEPRT software only until the second week of bloom.

Reprinted from Proceedings of the 1998 Beltwide Cotton Conferences pp. 1414 - 1416
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998