Broadleaf Weed Seedling Identification

Figure 1

Figure 1. Common lambsquarters

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One of the cornerstones of effective weed management plans is early and correct identification of weeds in a crop. Weed identification should determine herbicide selection, components of tank mixtures, rates, and application timing. Weed seedling identification is important because action needs to be taken before herbicide label guidelines are exceeded and to reduce weed competition with the crop. A good seedling weed identification resource is Common Weed Seedlings of the North Central States.1

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Figure 2

Figure 2. Waterhemp

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There are some general characteristics of broadleaf weeds that can be used during scouting to help identify weeds:

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  • Cotyledon (seed leaves) shape can be linear, oval, spatulate, lobed, or ovate
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  • True leaf shape, leaf margins, and venation (branching pattern of leaf veins)
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  • Leaf structure (simple or compound)
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    Figure 3

    Figure 3. Kochia

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  • Arrangement of leaves on the stem (alternate or opposite)
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  • Presence or absence of hairs on leaves or other parts of the plant
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Common weed seedlings that look similar include common lambsquarters, waterhemp, kochia, and giant ragweed (Figures 1-4). The following descriptions may help with correct identification:

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Figure 4

Figure 4. Giant ragweed

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Common lambsquarters – Small, linear cotyledons. Cotyledons and leaves are covered with white, mealy granules. First leaves are opposite, ovate with smooth margins. Waterhemp – Cotyledons are egg-shaped. Leaves are narrow, ovate to lanceolate, alternate and without hairs. Leaves may have a waxy appearance. Kochia - Narrow, oblong cotyledons covered with fine hairs. Leaves do not have petioles and are alternate, simple, hairy, and pointed. Giant ragweed - Oval to spatulate cotyledons with grooved petioles. Early leaves have dense hairs. Small seedlings are similar to common ragweed but giant ragweed cotyledons are much larger and green underneath, not purple, compared to common ragweed.

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Figure 5

Figure 5. Volunteer canola

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Anyone interested in distinguishing between volunteer canola (Figure 5) and other mustard species should consult the University of Idaho bulletin Mustards in Mustard.2