PS 445/545 - Weed Science Lab 1 Comprehensive Notes

Course Overview and Tentative Lab Schedule

• Course Identification: PS 445/545 - Weed Science (Lab 1)

• Institutional Identifier: Jackrabbits

• Tentative Lab Schedule and Grading Distribution:

  • Lab 1 (Aug. 25): Lab expectations; Intro to weed identification; Weed ID #1

  • Graded Component: Quiz #1 – Plant Features ($3\%$)

  • Lab 2 (Sept. 1): Weed ID #2 (broadleaves)

  • Graded Component: Quiz #2 - Weed ID ($5\%$)

  • Lab 3 (Sept. 8): Weed ID #3 (broadleaves); Intro to herbicide classification

  • Graded Component: Quiz #3 - Weed ID ($5\%$)

  • Lab 4 (Sept. 15): Weed ID #4 (grasses); Herbicide labels, formulations, adjuvants

  • Graded Component: Quiz #4 – Weed ID ($5\%$)

  • Lab 5 (Sept. 22): Weed ID #5 (noxious weeds, mixed)

  • Graded Component: Quiz #5 - Final Weed ID ($10\%$)

  • Lab 6 (Sept. 29): Herbicide dose calculations

  • Graded Component: Herbicide Dose Calculations assignment due ($7\%$)

  • Lab 7 (Oct. 6): Herbicides symptomology

  • Graded Component: Weed ID Portfolio due ($20\%$)

  • Lab 8 (Oct. 13): Herbicides symptomology; Weed scouting & management recommendations

  • Graded Component: Herbicides Symptomology assignment due ($9\%$)

  • Lab 9 (Oct. 20): Sprayer calibration

  • Lab 10 (Oct. 27): Hands-on sprayer calibration

  • Graded Component: Sprayer Calibration Calculations due ($7\%$)

  • Lab 11 (Nov. 3): Herbicides symptomology

  • Graded Component: Herbicides Symptomology - Quiz ($9\%$)

  • Lab 12 (Nov. 10): Weed management recommendations work

  • Graded Component: Weed Management Recommendations - Written ($7\%$) and Oral ($3\%$) reports due

  • Lab 13 (Nov. 17): Continuation of Weed Management Recommendations

  • Graded Component: Weed Management Recommendations – Written ($7\%$) and Oral ($3\%$) Reports Due

  • Lab 14 (Nov. 24): Scheduled lab topic session

  • Lab 15 (Dec. 1): Assessment

  • Graded Component: Lab Final ($10\%$)

Key Plant Features for Identification Overview

• Broadleaf Morphological Identifiers:

  • Venation

  • Attachment

  • Arrangement

  • Margin

  • Pubescence

  • Stipule

  • Bracts

  • Ocrea

• Grass Morphological Identifiers:

  • Sheath

  • Stem type

  • Growth habit

  • Leaf twist

  • Ligule

  • Auricles

  • Pubescence

Broadleaf Weed Identification and Morphology

• Vegetative Broadleaf Plant Structure & Definitions:

  • Cotyledon: The embryonic seed leaf; the first leaf structure to emerge.

  • Hypocotyl: The stem axis located directly below the cotyledons.

  • Epicotyl: The stem portion located directly above the cotyledons.

  • First True Leaves: The leaves that develop after the cotyledon emergence.

  • Petiole: The leaf stalk connecting the blade to the stem.

  • Midvein: The central, principal vein running down the leaf blade.

  • Leaf Base: The bottom section of the leaf blade near the petiole attachment.

  • Leaf Margin: The outer structural border edge of the leaf blade.

  • Leaf Tip: The apex or terminal point of the leaf blade.

  • Lobe: A distinct rounded or pointed division of a leaf blade.

  • Ocrea: A membranous sheath surrounding the stem node.

• Cotyledon and Leaf Shapes:

  • Standard Shape Classifications:

  • Linear

  • Lanceolate

  • Ovate

  • Oval

  • Oblong

  • Spatulate

  • Round

  • Round with Tapered Tip

  • Kidney

  • Butterfly

  • Species-Specific Cotyledon and True Leaf Comparisons:

  • Common ragweed: Features oval cotyledons with a lobed true leaf.

  • Tall morningglory: Features butterfly-shaped cotyledons with a heart-shaped true leaf.

• Leaf Arrangement Types:

  • Opposite Leaves: Paired leaves of similar size attached directly to opposite sides of the exact same node.

  • Alternate Leaves: One leaf attached per node. The newest emerging leaf is smaller than the preceding leaf.

  • Rosette / Whorled: Circular arrangement of leaves radiating from a central stem level.

  • Ecological Association: Common milkweed exhibits opposite leaf arrangement and serves as a host plant for specialized insects, including caterpillars of the monarch butterfly.

• Leaf Type Classifications:

  • Simple: A single unified leaf blade per petiole ($1$ blade per petiole).

  • Compound: Multiple distinct leaf blades attached to a single petiole ($>1$ blade per petiole).

  • Leaflet: Individual blade unit of a compound leaf.

  • Trifoliolate: A specialized compound leaf structure consisting of exactly $3$ leaflets.

• Leaf Venation Types:

  • Pinnate: Feather-like venation pattern originating off a central midvein.

  • Palmate: Hand-like venation pattern branching outward from a central point at the leaf base.

• Leaf Margin Types:

  • Butter Knife Margin (Entire/Smooth/Mildly Serrated): Exemplified by Prickly sida.

  • Steak Knife Margin (Coarsely Serrated/Toothed): Exemplified by Hophornbeam copperleaf.

• Leaf Attachment Variations:

  • Petiolate: Leaf blade attached to the main stem via a petiole.

  • Sessile: Leaf blade attached directly to the stem without a petiole stalk.

  • Clasping: Leaf base partially or completely encircles the main stem.

• Specialized Leaf-Related Structures:

  • Stipules:

  • Origin: Leaf base

  • Position: Located at the petiole base

  • Function: Protect young developing leaves or buds

  • Example: Rose

  • Bracts:

  • Origin: Modified leaf

  • Position: Located directly below the flower

  • Function: Protect flower or attract pollinators for the flower

  • Example: Fieldbind weed

  • Ocrea:

  • Origin: Fused stipules

  • Position: Surrounds the stem at the nodes

  • Function: Protect shoot growth points at the node

  • Example: Prostrate knotweed

Grass Weed Identification and Morphology

• Anatomical Components of a Grass Leaf:

  • Blade: Upper extended, flattened portion of the leaf.

  • Sheath: Lower tubular section wrapping around the stem.

  • Collar: The outer junction region between the blade and the sheath.

  • Ligule: Structure projecting on the inner side of the junction between the leaf blade and sheath.

  • Auricle: Claw-like appendage originating from the collar region.

• Ligule Variations:

  • Hairy Ligule: Represented by a ring or fringe of hairs. Example: Foxtail.

  • Membranous Ligule: Thin, translucent tissue. Examples: Shattercane, Wild oat.

  • Absent Ligule: Complete structural lack of a ligule. Example: Barnyardgrass.

  • Identification Rule: The ligule is typically absent on the first leaf of most grass species.

• Auricle Variations:

  • Prominent Clasping Auricles: Large appendages wrapping around the stem. Examples: Quackgrass, Jointed Goatgrass, Wheat, Barley, Rye.

  • Auricles Absent: Complete absence of auricles. Example: Most grass species.

• Leaf Twist Directions:

  • Clockwise Leaf Twist: Spiral orientation clockwise. Examples: Annual Bromegrass, Jointed Goatgrass.

  • Counter-Clockwise Leaf Twist: Spiral orientation counter-clockwise. Examples: Wild Oats, Oats.

  • No Distinct Twist: Flat growth with no helical twist. Example: Most grass species.

  • Identification Rule: The direction of leaf twist is consistent on first leaves only.

• Leaf or Sheath Pubescence (Hairiness):

  • Smooth: Glabrous, lacking hair structures.

  • Hairy: Possessing epidermal hairs.

  • Short Hair ("Fuzz"): Fine, abbreviated hair covering.

  • Long Hair: Extended hair structures.

  • Specific Species Examples:

  • Giant foxtail: Distinctly hairy.

  • Shattercane: Hairy along the sheath margin.

  • Yellow foxtail: Long hair present.

• Stem Types:

  • Round to Somewhat Flattened: Circular to semi-oval cross-section. Examples: Most common grasses, Yellow Foxtail, Sandbur, Barnyardgrass.

  • Distinctly Flat: Sharply compressed cross-section. Examples: Goosegrass, Orchardgrass, Barnyard grass.

• Growth Habit:

  • Developing Plant Stage:

  • Erect: Vertical growth direction. Example: Shattercane.

  • Decumbent (Reclining): Horizontal ground trailing with ascending ends. Example: Crabgrass.

  • Seedling Stage (First Leaves):

  • Erect: Upward leaf projection. Examples: Woolly cupgrass, Wild Oats, Annual Bromegrass.

  • Horizontal: Prostrate leaf projection. Examples: Woolly Cupgrass, Crabgrass.

• Modified Stems:

  • Stolon: A horizontal above-ground stem used to vegetatively propagate new plants. Example: Bermuda grass.

  • Rhizome: A horizontal below-ground stem used to vegetatively propagate new plants. Example: Johnsongrass.