Transcript Weeds (manual E, chapter 4)

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
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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. 2000. The Pesticide Book, 5th Edition.