Effects of Pre-emergent Weed Control Products on Container Grown Herbaceous Ornamentals

Although there are many preemergent herbicides currently marketed for use in large-scale production of agronomic crops, the use of these products on horticultural crops may be prohibited if the name of the crop does not appear on the product label.  An objective of the IR-4 Project’s Ornamental Horticulture Program (http://ir4.rutgers.edu/ornamentals.html) has been to determine the effects of selected pest control products on ornamental crops.  For many years, researchers at Colorado State University have evaluated the effects of selected weed control products on container-grown ornamentals.  During 2012, Biathlon 2.75G, Echelon 4SC, Freehand 1.75G, and Indaziflam G were evaluated at one-, two-, and four-times the label rate (1X, 2X, & 4X rates, respectively); Gallery 75DF was evaluated only at the 4X rate.  Control containers received no herbicide product. Delosperma nubigenum, Delosperma cooperi, Helianthus salicifolius 'Low Down’, Petunia hybrida ‘Cascadias Blue Dream’, Sedum spurium 'Dragon's Blood’, and Sedum spurium 'Red Carpet’ were the plant taxa used in the study.  Each herbicide product was not evaluated on every plant taxa.  Each plant taxa and herbicide product interaction constituted an experiment; each experiment was comprised of three blocks, and each block contained five replications of each treatment plus controls.  Blocks were randomly arranged within the study area, and treatments were randomly arranged within each block. Plants were grown in an organic growing medium in number 1 black plastic containers, and irrigated daily.  Herbicide products were applied two times during the ten-week evaluation period; the first application occurred a few days after plants were transplanted into the containers, and the second occurred six weeks later. Plants were measured at the beginning and end of the evaluation period. At the end of the evaluation period, plants were harvested, oven dried, and then weighed.  Echelon 4SC at all three rates caused distorted and necrotic tips on young leaves and significantly reduced the size of Delosperma nubigenum, at the 2X and 4X rates significantly reduced the size of Petunia hybrida ‘Cascadias Blue Dream’, and at the 4X rate significantly reduced the size of Sedum spurium 'Red Carpet’. Freehand 1.75G at the 4X rate caused chlorosis of young leaves and significantly reduced the size of Helianthus salicifolius 'Low Down’.  Gallery 75DF at the 4X rate significantly reduced the size of Delosperma nubigenum and Sedum spurium 'Red Carpet’.  Indaziflam G at the 4X rate caused chlorosis of young leaves of Delosperma cooperi and Sedum spurium 'Dragon's Blood’.