Chemical pinching of Chrysanthemum x morifolium Ramat. with undecanol

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Virginia Polytechnic Institute and State University

Concentrations between 5000 and 15000 mg/liter undecanol applied as foliar sprays were effective in pinching most varieties of chrysanthemum tested. Cultivars varied in their response. Subapical phytotoxicity increased with increasing concentrations and was generally more variable among cultivars than was the pinch response. Concentrations effective in pinching without subapical phytotoxicity resulted in plants similar to manually pinched plants with respect to height and number of branches.

Studies conducted in the growth chamber and greenhouse indicate environmental factors exert a major influence on plant response to undecanol. In general, conditions which favor more rapid drying tended to decrease the number of plants pinched and reduce the number of plants showing subapical phytotoxicity. Comparing air temperature, air flow, relative humidity, and light (PAR), temperature was the single most highly correlated environmental variable with both pinching and phytotoxicity in the greenhouse study. Many of these variables are, however, highly interrelated with one another so that a change in one results in a change in others. Prediction equations using concentration and environmental variables were developed for pinching and phytotoxicity.

Undecanol foliar sprays of 7500 mg/liter were nearly 100% effective in pinching two cultivars with minimal phytotoxicity when applied 9 to 18 days after planting. Pinching was significantly reduced in plants treated prior to 9 or later than 18 days after planting. Manually pinched plants were generally taller than chemically pinched plants treated the same day. Chemically pinched plants generally produced more branches than manually pinched plants. Day of treatment did not affect flowering of chemically pinched plants; however, chemically pinched plants tended to flower slightly later than manually pinched plants. Finished plants pinched chemically were comparable to those produced by manual pinching.