Plant Morphology and a Seedling Identification Key to ID Weeds

5/14/2020

Chris Proctor

2020 Crop Scout Training

Carry your Weed ID Guide

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Life Cycle Annuals

Complete life cycle within 12 months

Reproduce by seed

Winter Annuals

Summer Annuals

Life Cycle Biennials

Require two years to complete life cycle Vegetative first year Rosette Reproductive second year Bolt Common mullein

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Life Cycle Perennials

Requires more than two years to complete life cycle Herbaceous Vegetative first year Reproductive second year Extensive root system Vegetative Reproduction (rhizomes, stolons) Quackgrass Johnsongrass

Broadleaf Plants

Cotyledons Branched Stems 1st True Leaf(s) 2nd True Leaf(s) Example: Soybeans

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Broadleaf Plant Parts (pg. 66)

Common Leaf and Cotyledon Shapes

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Common Leaf and Cotyledon Shapes

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True Leaves

Emerge after cotyledons

Simple Pinnately Palmately Compound Compound

Leaf Structure?

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Leaf Margins

Leaf Margin type?

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Leaf Position

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Opposite

Opposite, then alternate

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Alternate

Ocrea

Occurs in the Polygonaceae (Buckwheat) family

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Identifying Grass Weeds

Grass and grass-like plants Grasses Monocot Hollow stems and nodes Leaves are 2-ranked Parallel veins Example: Corn Grass-like plants Solid Stems without nodes Leaves are 2-or 3-ranked and have parallel veins Example: Yellow nutsedge

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Plant Parts

Stem or Sheath Shape

Grass stems are round to somewhat flattened or distinctly flattened If in doubt, the stem is probably not distinctly flattened.

Nutsedge is not a grass and has a triangular stem

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Distinctly Flattened Stem

Sandbur viewed at right angles

Collar

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Ligule

A projection at the base of the leaf blade Membranous: a solid, shiny projection Hair-like: a fringe of hairs Absent: most seedlings do not have a ligule on the first 1-2 leaves Example: Barnyardgrass Pull leaf back from stem May require a hand lens to see

Ligule

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Membranous Ligule

Membranous ligules may

and appear hairlike

Hair-like Ligule

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Membranous or Hair-like?

Leaf and Sheath Pubescence (Hair)

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Blade Width and Length Short wide vs. long narrow

Sheath Margins

Split United

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Leaf Auricles

from the base of the leaf

May dry up and disappear as plant ages

Leaf Midrib or Midvein

Most leaf midveins are faint or obscure

A few grasses have prominent midvein Wider, lighter color and may be prominent below

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Growth Habit Seedling

Growth Habit Developing Plant

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Leaf Twist

While most seedling grass leaves may twist in random directions, a few have prominent twist (on first leaves)

Seed Size and Shape

Grass seed can be an important clue to the identity of small grass seedlings.

The seed of grasses often remains attached to the primary root after germination

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Identifying Grass Weeds

1. Stem shape? 2. Ligule type? 3. Hair on blade and sheath? 4. Blade width or length? 5. Sheath margins? 6. Auricles? 7. Growth habit?

Use the IPM Field Scout Guide Key to identify this weed

1. Identify the cotyledon shape.

Page 66-67 2. Are the first true leaves alternate or opposite?

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Keying out a broadleaf seedling

3. Is an ocrea present?

4. Large cotyledons with prominent, recessed midvein?

Keying out a broadleaf seedling

5. Nick in tip of first true leaves? Stem reddish-violet?

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Keying out a broadleaf seedling

6. Smooth or hairy? 7. Rough or glossy? 8. Leaf Shape?

Distinguishing similar species

Palmer Amaranth

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Weeds not in the key?

Look in the boxes at the bottom

Grass Seedling I.D. Key

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QUESTIONS? CropWatch.unl.edu @UNL_CropWatch

Email: [email protected]

Chris Proctor

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