Through contacts, observations, and travel throughout the midwestern United States during Spring and Summer 2004, a number of weed species were noted to be relatively new problems, or growing problems in turfgrass and/or horticultural cropping situations. These include hophornbeam copperleaf (Acalyphaostryifolia), garlic mustard (Alliaria petiolata), blackgrass (Alopecurus myosuroides), Palmer amaranth (Amaranthuspalmeri), waterhemp species (Amaranthus spp.), biennial wormwood (Artemisiabiennis), lambsquarters complex species (Chenopodium spp.), windmillgrass (Chlorisverticillata), showy chloris (Chlorisvirgata), Asiatic dayflower (Commelinacommunis), horseweed (Conyzacanadensis), redstem filaree (Erodiumcicutarium), toothed spurge (Euphorbia dentata), dovefoot geranium (Geranium molle), pitted morningglory (Ipomoealacunosa), purple deadnettle (Lamium purpureum), birdsfoot trefoil (Lotuscorniculatus), roundleaf mallow (Malvarotundifolia), star-of-bethlehem (Ornithogalumumbellatum), cressleaf groundsel (Packeraglabella), striate knotweed (Polygonum erecta), creeping yellow fieldcress (Rorippa sylvestris), lanceleaf sage (Salviareflexa), sibara (Sibaravirginica), white campion (Silene latifolia ssp. alba), hairy nightshade (Solanumphysalifoium), spiny sowthistle (Sonchusasper), and others. Possibilities for this increase or spread include natural invasiveness of the weeds, control of previous weed competitors, resistance to widely used herbicides, changes in cropping practices, and other weed adaptations to current weed management methods.
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