Weeds Category E Turf and Ornamental Pesticide Applicator Training Manual Chapter 4

Introduction In this chapter you need to understand: Why weeds are important. When a plant is a weed. Damage weeds can cause. Identify some Minnesota plants considered weeds.

Terms Broadleaf weeds—dicots that are growing where they are not wanted. Grassy weeds—monocots that are growing where they are not wanted. Category E--- Chapter 4 Weeds

Why Weeds are Important Weeds: –Detract from the appearance of the landscape. –Compete with desirable plants for space, nutrients, and water. –Can provide habitat for other plant pests.

What’s a Weed? Any unwanted plant. A plant can be invasive into desired plants –Some produce large amounts of seed. –Some can reproduce vegetatively (roots and stems) through normal cultural practices e.g. Mowing. –Legally declared weeds by the State of Minnesota e.g. Canadian thistle or local governments e.g. common buckthorn in Minneapolis

Potential Damage from Weeds Compete with ornaments for water, nutrients, light, and space. Can interfere with management practices e.g. planting, thinning. Some weeds produce substances that inhibit growth of other plants (allopathy). Some weeds produce irritating or poisonous substances.

Weed Identification Turfgrass weeds fall into 2 groups: –Grassy—monocots (have a single leaf on emergence). Examples: crabgrass, quackgrass, tall fescue. –Broadleaf —dicots (have 2 leaves on emergence). Examples: dandelion palntain.

Weed Identification Dandelion Low-growing perennial. Rosette habit. Thick roots. Plant can regenerate from small root or stem segments. Tiny seeds can disperse great distances. Thrive in weak, thin turf.

Weed Identification Common Chickweed Creeping annual weed. Small, pale green weeds and petioles. Grows best in cool, wet weather. Shade tolerant. To help prevent— Maintain a dense turf and water infrequently

Weed Identification Crabgrass Coarse blades, light green. Can germinate the entire season after the soil warms. To help prevent— maintain a dense, healthy turf. Apply preemergent after soil reaches 55°F.

Weed Identification Foxtail Annual grass, has long hairs on the upper surface of the leaf blade and cylindrical yellow seedheads.

Weed Identification Canada Thistle Perennial weed spread by seeds and creeping roots (can extend up to 20 feet). Large numbers of wind-dispersed seeds. Destroy by digging out roots or some herbicides.

Weed Identification Quackgrass Perennial grass spread by rhizomes. Cannot be controlled with shallow cultivation— requires deep tilling.

Weed Identification Prostrate Knotweed Annual, low-growing. Very competitive in compacted,high traffic, infertile soil.

Weed Identification Prostrate Spurge Annual, low-growing. Reddish or green prostrate stems. Often found on poorly fertilized soils. To help prevent—maintain a dense, healthy turf. Apply preemergents when soil 60-65°F.

Weed Identification Bindweed Perennial, vining herb. Extensive root system, hard to control. Pull out or cut root 3-6 inches below the surface.

Weed Identification Purslane Annual, fibrous root system. Stems smooth, often reddish and prostrate. Common in cultivated areas. Difficult to control with cultivation.

Weed Identification Ground Ivy Perennial, creeping growth habit, forms dense patches. Grows well in shady, poorly drained areas.

Weed Identification White Clover Perennial, low-growing. Will root from nodes. Competes effectively with established lawns—especially in moist conditions and low fertility.

Herbicides Nonselective herbicide—a chemical that is generally toxic to plants without regard to species…. Preemergent—prior to the emergence of the specified weed or crop. Postemergent—after the emergence of the specified weed or crop. Credit: Ware, G.E The Pesticide Book, 5 th Edition.