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 weedsdicots that are growing where
  they are not wanted.
• Grassy weedsmonocots 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
Whats 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
• Grassymonocots (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 preventMaintain a dense turf and water
  infrequently

10
Weed IdentificationCrabgrass

• Coarse blades, light green.
• Can germinate the entire season after the soil
  warms.
• To help preventmaintain a dense, healthy turf.
• Apply preemergent after soil reaches 55F.

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
  cultivationrequires 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 preventmaintain a dense, healthy turf.
• Apply preemergents when soil 60-65F.

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
  lawnsespecially in moist conditions and low
  fertility.

20
Herbicides

• Nonselective herbicidea chemical that is
  generally toxic to plants without regard to
  species.
• Preemergentprior to the emergence of the
  specified weed or crop.
• Postemergentafter the emergence of the specified
  weed or crop.

Credit Ware, G.E. 2000. The Pesticide Book,
5th Edition.