Pix Effects on Earliness and Fruit Retention of Contrasting Cotton Varieties

C.O. Gwathmey, O.M. Wassel, and P.E. Hoskinson


Pix® (mepiquat chloride) may increase early fruit retention more in later maturing, indeterminate cotton cultivars than in early maturing cultivars that are more physiologically determinate. A field study was conducted at the West Tennessee Experiment Station in 1993 to detect changes in earliness and fruit retention of three contrasting cultivars in response to low-rate multiple (LRM) applications of Pix, and possible effects on lint yields. This study was part of a larger, ongoing investigation of effects of single and multiple Pix applications on a range of newer cotton cultivars adapted to West Tennessee. Experimental design was a RCB split-plot, with LRM Pix and a check as main-plot treatments, and varieties (Stoneville 132, DES 119, and Stoneville La 887) as subplot treatments. Varieties were planted in 1-m rows on 17 May, and conventional tillage and crop management practices were followed. Supplemental irrigations and insecticide applications reduced stresses during reproductive development. LRM Pix treatments (each 12.3 g a.i. ha-1) were applied at 51, 58, 65, and 72 days after planting. Plant height, mainstem node number, and fruiting at first-position sympodial sites were monitored on seven plants in each subplot during and after the Pix treatment period. Two center rows of each subplot were spindle picked for yield determination on 5 and 26 October.

Pix significantly reduced plant height in all varieties, from 18% in the earliest maturing variety, STV 132, to 34% in the latest and least determinate variety, STV La 887. Pix also reduced mainstem node numbers of these two varieties by 0.6 and 2.4 nodes, respectively. DES 119 exhibited an intermediate response. Pix-induced reductions in node numbers were associated with fewer nodes above white bloom and earlier cutout (by about 2 to 4 days) in all cultivars. DES 119 exhibited a slightly lower rate of flowering than the Stoneville varieties, but a similar cutout response to Pix. From midbloom to cutout, square retention remained relatively stable in STV La 887, but significantly decreased in Pix-treated STV 132. During the same period, boll retention tended to increase in all treatments except Pix-treated STV 132. Between cutout and harvest, however, first position boll retention declined in all treatments and ranged from 37% to 49% prior to first harvest. Varieties differed significantly in final boll set, but Pix effects and interactions were not statistically significant. Percent open bolls and percent yield at first harvest were consistently but not significantly higher with Pix application to all varieties. Untreated STV 132 yielded 1117 kg ha-1 lint at first harvest, significantly more than STV La 887 (911 kg ha-1) or DES 119 (842 kg ha-1). Pix tended to increase first harvest yields (by 9 and 16% respectively) in the latter varieties, but not in STV 132. Pix effects on lint yield were not statistically significant. Data suggest that varieties may differ in earliness and fruiting responses to Pix, and that further research is needed to develop variety-specific recommendations.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1325
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998