Revised June 2007

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Contents

• Principles of weed identification
• Weed scouting and mapping procedures
• Economic thresholds for weeds
• Herbicide injury
• Factors contributing to herbicide injury

Weed identification

Herbicides

• Herbicide mode of action families
• Growth regulators
• Amino acid synthesis inhibitors
• Lipid synthesis inhibitors
• Seedling growth inhibitors
• Photosynthesis inhibitors
• Cell membrane disruptors
• Pigment inhibitors

Related pages

• G1886, Controlling Drift of Crop Protection Materials
• IPM1021, Vine Weeds of Missouri
• IPM1023, Missouri Weed Seeds

Other related Web sites

• MU Extension Plant Diagnostic Clinic
• WeedSOFT™ yield loss calculator

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Practical Weed Science for the Field Scout: Corn and Soybean

Perennial broadleaf

Thistle, Canada (Cirsium arvense)

A perennial from creeping horizontal rhizomes that is generally a weed of no-till cropping systems, pastures, and noncrop areas. Seedlings have dull green thick cotyledons and young leaves that are covered with short hairs. Mature leaves are alternate, irregularly lobed, with spiny margins and without hairs on the upper surface. Flowers are pink or purple, typically 3/4 inch in diameter with spineless bracts beneath unlike musk or bull thistle.

IPM1007, revised June 2007