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Field Evaluations of Morphactins and Other Growth Regulators for Senescence Delay of Flax, Soybean, Wheat, and Oats¹

Field trials were conducted from 1975 through 1979 to detect chemicals which would delay senescence of flax (Linum usitatissimum L.), soybean [Glycine max (L.) Merrill], wheat [Triticum aestivum (L.) em Thell], and oats (Avena sativa L.). Of 18 regulators tested 2 or more years on flax, 11 delayed leaf yellowing after single applications in at least I year. The morphactin chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate), applied postbloom at rates of 25 to 50 g/ha retarded losses of chlorophyll and leaf area and promoted shoot growth and flowering. Early-flowering cultivars were more responsive than late cultivars. Dichlorflurenol (methyl 9,7-dichloro-9-hydroxyfluorene-9-carboxylate) and n-butyl flurenol (n-butyl 9-hydroxyfluorene-9-carboxylate), were slightly less and markedly less effective than chlorflurenol, respectively. Other regulators which were effective when applied postbloom were 3-CPA (2-(3-chlorophenoxy)propionamide), TIBA (2,3,5-triiodobenzoic acid), ethephon (2-chloroethyl)phosphonic acid), SD-8339 (N- (phenylmethyl)-9-(tetrahydro-2H-pyran-2-yl)-9- H-purin-6-amine), BA + GA_4,7(6-(benzylamino) purlne plus gibberellins 4 and 7), and PP528 (ethyl 5-(4-chloro-phenyl)-2H-tetrazole-2-acetate). Treatments made earlier than postbloom often resulted in growth abnormalities. Combination of cytokinin or gibberellin with other regulators usually did not enhance effectiveness.

Chlorflurenol delayed yellowing of ‘Swift’ soybean when applied in R5 stage at rates of 25 and 50 g/ha. Applications at higher rates or earlier dates caused growth abnormalities. Other effective chemicals included dichlorflurenol, BA, and BA + GA_4,7. For oats and wheat, chlorflurenol was ineffective when applied from boot stage to postanthesis at rates up to 1000 and 2000 g/ha, respectively.

Key Words: Chlorflurenol • Dichlorflurenol • n-Butyl flurenol • Flurecol • 3-CPA • GA₃ • GA₄,₇ • BA + GA₄,₇ • Cytex • Chlormequat • TIBA • Ethephon • Naptalam • PP528 • NC 9634 • 2,4,6-T • Chlorophyll • Crop yield

² Research plant physiologist, Agricultural Research Science, Science and Education Administration, USDA, and assoc. professor, South Dakota State Univ., respectively.

Received for publication December 15, 1980.