University of Arizona a dot Cooperative Extension

Mepiquat Chloride (MC) Application Guidelines for Arizona Cotton
(Publication az1211)
(PDF file version, 47KB)

by Jeffrey C. Silvertooth,
Extension Agronomist - Cotton


Follow Fruit Retention (FR) and Height:Node Ratios (HNR) vs. Heat Units After Planting (HUAP)

  • Reference: HNR & FR baselines with upper and lower thresholds, Figures 1 & 2 (J.C. Silvertooth et al. UA)

    IF HNRs are trending toward, equal, or exceed upper HNR thresholds (Fig. 1)

    • vegetative tendancies are very likely
      • evaluate fruit retention (FR) levels also, (see Figure 2)
      • should confirm vegetative condition
    • consider initiation of MC treatments
    • follow rate guidelines (see Table below)
    • follow crop response (HNRs)

    IF HNRs are near the baseline (middle line on figures)

    • plant height (vegetative) control is not a problem
    • withold MC applications

    IF HNRs are near lower HNR threshold

    • crop may have been under some degree of stress
    • evaluate crop for possible causes of reduced vegetative structure
    • withold MC applications

Continue to monitor field development on a regular basis: follow HNR and FR conditions in relation to baselines

Table 1. Suggested Mepiquat Chloride (MC) application rates*


0.5 pt./acre


1.5 pt./acre

General Optimum

0.75 pt./acre

*Based on University of Arizona research (J.C. Silvertooth, et al.)

height/node ratio for Upland and Pima cotton

fruit retention guidelines for Upland and Pima cotton

Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.

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Information provided by Jeffrey C. Silvertooth,
Extension Agronomist - Cotton, College of Agriculture, The University of Arizona.
Material written June 2001.

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