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Rick A. Boydston, Harold P. Collins and Steven F. Vaughn

This research evaluated the use of dried distiller grains with solubles (DDGS) as a soil amendment to suppress weeds in container-grown ornamentals. DDGS is a byproduct of ethanol produced from corn, and developing new uses for DDGS could increase the profitability of ethanol production. Adding DDGS to a commercial pine bark potting mix reduced emergence and growth of common chickweed (Stellaria media) at concentrations of 5% (by weight) or greater and annual bluegrass (Poa annua) at concentrations of 10% (by weight) or more. Herbicidal activity of DDGS was maintained in methanol-extracted DDGS. Rosa hybrid ‘Red Sunblaze’, Phlox paniculata ‘Franz Schubert’, and Coreopsis auriculata ‘Nana’ transplanted into potting soil amended with 20% by weight DDGS were severely stunted and nearly all plants died. Plants survived when transplanted into potting soil containing 10% DDGS by weight, but growth was greatly stunted and flowering of rose and coreopsis was reduced. Addition of 20% DDGS decreased the C:N ratio from 90:1 to 24:1 for the potting mix and from 23:1 to 10:1 for a soil. The decrease in C:N ratio resulted in a twofold increase in microbial respiration at 3 d and 14 d of incubation for both the potting mix and soil. As a result of the phytotoxicity observed on ornamentals transplanted into DDGS-amended potting soil, subsequent studies evaluated surface-applied DDGS to suppress weeds. DDGS applied at 400 g·m−2 or less to the soil surface at transplanting did not reduce emergence or growth of common chickweed or annual bluegrass. DDGS applied at 800 and 1600 g·m−2 to the surface of transplanted ornamentals reduced number of annual bluegrass by 40% and 57% and common chickweed by 33% and 58%, respectively, without injury to transplanted ornamentals. DDGS may be useful for reducing weed emergence and growth in container-grown ornamentals applied to the soil surface at transplanting.

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Martin M. Williams II, Rick A. Boydston and Adam S. Davis

Research in dent corn has found significant variation in crop/weed competition for light among hybrids. However, little has been published on the extent of variation in sweet corn competitive ability. Field studies were conducted under weed-free conditions to quantify canopy development and light environment among three sweet corn hybrids and to determine associations among canopy characteristics to crop yield. An early-season hybrid (Spirit) and two midseason hybrids (WHT2801 and GH2547) were grown at experimental sites located near Urbana, Ill., and Prosser, Wash., in 2004 and 2005. Maximum leaf area index (LAI) and intercepted photosynthetically active radiation (PAR) was typically highest for GH2547 and lowest for Spirit. Most differences in vertical LAI among hybrids was observed above 60 and 150 cm in Illinois and Washington, respectively, with WHT2801 and GH2547 having leaf area distributed higher in the canopy than Spirit. Both number and mass of marketable ears were positively correlated with maximum relative growth rate (correlation coefficients 0.60–0.81), leaf area duration (0.68–0.79), total LAI (0.56–0.74) at R1, and intercepted PAR (0.74–0.83) at R1. Differences in canopy properties and interception of solar radiation among Spirit, WHT2801, and GH2547 lead us to hypothesize that variation in weed-suppressive ability exists among hybrids. Future testing of this hypothesis will provide knowledge of interactions specific to sweet corn useful for developing improved weed management systems.

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Rick A. Boydston, Treva Anderson and Steven F. Vaughn

Mustard seed meal is a byproduct of mustard (Sinapis alba L.) grown for oil production. Developing new uses for mustard seed meal could increase the profitability of growing mustard. Seed meal of mustard, var. ‘IdaGold’, was applied to the soil surface to evaluate its effect on several common weeds in container-grown ornamentals. Mustard seed meal applied to the soil surface of containers at 113, 225, and 450 g·m−2 reduced the number of annual bluegrass (Poa annua L.) seedlings by 60%, 86%, and 98%, respectively, and the number of common chickweed (Stellaria media L.) seedlings by 61%, 74%, and 73%, respectively, at 8 weeks after treatment (WAT). Mustard seed meal applied to the soil surface after transplanting Rosa L. hybrid, var. ‘Red Sunblaze’, Phlox paniculata L., var. ‘Franz Schubert’, and Coreopsis auriculata L., var. ‘Nana’ did not injure or affect the flowering or growth of ornamentals. In separate experiments, mustard seed meal applied at 225 g·m−2 to the soil surface reduced the number of emerged seedlings and fresh weight of creeping woodsorrel (Oxalis corniculata) 90% and 95%, respectively, at 8 WAT. Mustard seed meal applied at 450 g·m−2 completely prevented woodsorrel emergence at 8 WAT. Mustard seed meal applied postemergence to established liverwort (Marchantia polymorpha L.) at 113, 225, and 450 g·m−2 did not injure container-grown Pulsatilla vulgaris Mill., var. ‘Heiler Hybrids Mixed’ up to 6 WAT and controlled liverwort from 83% to 97% at 6 WAT. Weed suppression with mustard seed meal generally increased as rate increased from 113 to 450 g·m−2. Mustard seed meal may be useful for selective suppression of annual weeds when applied to the soil surface of container-grown transplanted ornamentals.