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

WeedsWeeds

Category E Turf and Ornamental

Pesticide Applicator Training Manual Chapter 4

IntroductionIntroduction• 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.

TermsTerms• 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 ImportantWhy 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 WeedsPotential 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 IdentificationWeed 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 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.

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

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.

Weed IdentificationFoxtail

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

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.

Weed IdentificationQuackgrass

• Perennial grass spread by rhizomes.

• Cannot be controlled with shallow cultivation—requires deep tilling.

Weed IdentificationWeed IdentificationProstrate KnotweedProstrate Knotweed

• Annual, low-growing.• Very competitive in

compacted ,high traffic, infertile soil.

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.

Weed IdentificationBindweed

• Perennial, vining herb.• Extensive root system,

hard to control.• Pull out or cut root 3-6

inches below the surface.

Weed IdentificationPurslane

• Annual, fibrous root system.

• Stems smooth, often reddish and prostrate.

• Common in cultivated areas.

• Difficult to control with cultivation.

Weed IdentificationGround Ivy

• Perennial, creeping growth habit, forms dense patches.

• Grows well in shady, poorly drained areas.

Weed IdentificationWeed IdentificationWhite CloverWhite 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. 2000. The Pesticide Book, 5th Edition.