Weeds

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

2. 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.

3. 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

4. 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.

5. 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

6. 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.

7. 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.

8. Weed IdentificationDandelion • 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.

9. Weed IdentificationCommon 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

10. Weed IdentificationCrabgrass • 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.

11. Weed IdentificationFoxtail • Annual grass, has long hairs on the upper surface of the leaf blade and cylindrical yellow seedheads.

12. Weed IdentificationCanada 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.

13. Weed IdentificationQuackgrass • Perennial grass spread by rhizomes. • Cannot be controlled with shallow cultivation—requires deep tilling.

14. Weed IdentificationProstrate Knotweed • Annual, low-growing. • Very competitive in compacted ,high traffic, infertile soil.

15. Weed IdentificationProstrate 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.

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

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

18. Weed IdentificationGround Ivy • Perennial, creeping growth habit, forms dense patches. • Grows well in shady, poorly drained areas.

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

20. 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. 2000. The Pesticide Book, 5th Edition.