Chemical Removal of Early Squares: Treatment Efficacy and Effects on Reproductive Growth of Superokra-Leaf Cotton

C.W. Kennedy and J.E. Jones


Chemical removal of early squares would facilitate trapping early generations of boll weevil (Anthonomus grandis Boh.). Previous research has shown that determinate-type superokra-leaf cotton was more able to compensate for early square removal than the less determinate, normal-leaf counterpart. Research on chemical removal of squares showed ethephon to be effective at square removal but potentially destructive to plant growth. Alternatively, Ag+ has been found to be a potent inhibitor of ethylene action. The objectives of this study were to determine treatment efficacy of early-square removal, determine any ameliorating effects of a pretreatment of 200 mg 1-1 AgNO3 on plant terminals and to determine resultant effects on reproductive growth of field-grown, superokra-leaf cottons [Lal363, L(s)ne(Lal363) and La2l3-16303-613 L(s)(LS213)].

Ethephon applications of 8mM and 12mM ethephon at a rate of 0.28 kg ha-1 and 2OmM ethephon at 0.68 kg ha-1 effectively removed squares, but were more variable compared to manual square removal. In 1986, ethephon treatments removed squares that could not be easily removed by hand and thus were 75% more efficient than the manual square removal. In 1987 and 1988, etephon treatments had an equivalent or lower efficiency compared to manual square removal. The pretreatment application of 200 mg 1-1 AgNO3 tended to reduce efficacy of square removal in ethephon treatments.

The onset of blooming was delayed by square removal, followed by a generally faster blooming rate. The increased rate of blooming did not completely compensate for the delays as blooming periods in square removal treatments extended beyond that of controls. The total number of blooms produced was not significantly affected by treatment. Percent retention of blooms to mature bolls was significantly lower for BmM and 12mM ethephon applications in 1988 only.

Treatment effects on machine-picked seedcotton yields were variable between years. In 1986, 2OmM ethephon ± AGNO3, 8mM ethephon - AgNO3, and 12mM ethephon - AGNO, had significantly lower yields than controls. In 1987, manual, and 12mM ethephon - AgNO3 produced significantly more seedcotton than controls for both Lal363 and LS213. In 1988, LS213 produced significantly less yield in the BmM ethephon - AgNO3 treatment, while Lal363 produced significantly less in the 12mM ethephon - AgNO3 treatment. Differences in seedcotton yield in 1987 and 1988 were attributed to differences in the number of bolls produced while differences between controls and 20mM ethephon ± AgNO3 in 1986 were attributed to the amount of seedcotton produced per boll.

The use of ethephon to remove early squares delayed crop maturity. Percent of total seedcotton at first hand-harvest was 23 - 67% less than controls for ethephon treatments in 1986, 6 - 30% in 1987, and 0 - 24% in 1988. LS213 had significantly lower percent of total seedcotton at first harvest than Lal363 in the 12mM ethephon treatments in 1987 and 1988. The reduction in percent of total seedcotton at first pick was related to the number and percent of sites that abscised a square. Residual, unspecified effects of ethephon on plant growth, however, could not be ruled out in the delay of crop maturity or in yield response.

Reprinted from 1990 Proceedings: Beltwide Cotton Production Research Conferences pg. 53
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998