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Agronomic Weeds 1 CS 414 Note: weeds occur in a variety of sites, management schemes, & niches. These weeds are commonly (not exclusively) found in agronomic systems. Slide 2 Amaranthus hybridus Amaranthaceae Smooth pigweed Summer annual, stems densely pubescent Stems erect & slender Upper stem is densely hairy Slide 3 Amaranthus palmeri Amaranthaceae Palmer amaranth Summer annual, alternate, glabrous leaves Petioles generally longer than blade White chevron visible on leaves Becoming a problematic weed as resistance develops Slide 4 Amaranthus retroflexus Amaranthaceae Redroot pigweed Summer annual, hairs along leaf margins, especially on lower leaf surfaces Petioles , wavy margins Shallow taproot, usually reddish in color Dense, terminal seed head (not many seed heads as on Palmer) Slide 5 Amaranthus spinosus Amaranthaceae Spiny amaranth Summer annual, similar to other pigweeds, but has spines along stem Stems below cotyledons are red Long petioles, no hairs Pairs of spines at base of most petioles Slide 6 Ambrosia artemisiifolia Asteraceae Common ragweed Summer annual Round stem, smooth underside of leaf, sdlgs look like marigolds, rounded lobes on leaves Slide 7 Eclipta prostrata Asteraceae eclipta Summer annual Freely branching, reddish stem, opposite leaves are hairy and toothed. Slide 8 Eupatorium capillifolium Dogfennel Asteraceae Perennial Resembles asparagus-fern, sdlg leaves highly dissected Slide 9 Common cocklebur Xanthium strumarium Asteraceae Summer annual Rough leaf texture, black spots on stem Slide 10 Chenopodium album Amaranthaceae Common lambsquarters Summer annual Purple-tint on stems, mealy texture on leaves, esp. on top of plant Slide 11 Common Name: tropic croton Family: Euphorbiaceae Genus: Croton Species: glandulosus summer annual serrated leaves and white, disc-like glands that occur above and below the petiole at the point of attachment to the stem leaves of eclipta are much more linear in outline and are arranged oppositely along the stem unlike the alternate leaves of tropic croton stems of tropic croton are hairy Slide 12 Crotalaria spectabilis Fabaceae Showy crotalaria Summer annual to 6 ft, stems waxy with age, taproot Upper leaf blade glabrous, lower leaf blade with appressed hairs Yellow flowers, seedpod resembles pea pod when ripe Slide 13 Cassia obtusifolius Fabaceae Sicklepod Summer annual, rounded cotyledons with distinctive veining, late emergence (June- July) Stems erect, glabrous Leaves opposite with 4 to 6 egg-shaped leaflets Seedpod is long & narrow, seed similar in dimensions to soybean Slide 14 Sesbania exaltata Fabaceae Hemp sesbania Erect summer annual, becomes woody with age Pinnately compound (6-8 leaflets) arranged oppositely Legumes are long and narrow, many seeds Slide 15 Vicia spp. Fabaceae Vetches Herbaceous annuals & perennials, typically trailing/vining stems Typical legumes leaves opposite & pinnately compound Fruit is a legume (pod) Tendrils develop on older leaves Often used as cover crops or in natural plantings Slide 16 Abutilon theophrasti Malvaceae Velvetleaf (buttonweed) Summer annual, usually unbranched, covered with soft hairs Heart-shaped cotyledons Taproot Flowers yellow with 5 petals Slide 17 Common Name: spurred anoda Family: Malvaceae Genus: Anoda Species: cristata summer annual Seedlings with 1 round and 1 heart-shaped cotyledon plants with triangular- shaped, coarsely-toothed leaves, pubescent on both sides Slide 18 Hibiscus trionum Malvaceae Venice mallow Summer annual, leaves 3 or 5 lobed/deeply cut Leaves alternate, coarse teeth Shallow taproot Flowers open only for a few hours in AM Yellow petals with purple bases Seeds pubescent Slide 19 Sida rhombifolia Arrowleaf sida Malvaceae Summer annual First true leaf is toothed. Leaf widest at middle, spines at base of leaves and stems. Leaf shape is key! Slide 20 Sida spinosa prickly sida Malvaceae Summer annual First true leaf not as toothed as S. rhombifolia. Leaf shape is key! Spinier than S. rhombifolia. Slide 21 Oenothera laciniata Onagraceae Cutleaf eveningprimrose Biennial or winter annual (rarely summer) Leaves with deeply toothed margins, red & yellow flowers Cotyledons long & thin, plant begins as basal rosette Habit can be erect or prostrate