YOUTH & FAMILIES AGRICULTURE HEALTH ECONOMY ENVIRONMENT ENERGY COMMUNITIES

Session 2:

Weed Reproduction

Annual Weed Success

• Weed seeds often

germinate (or

seedlings emerge)

more quickly than

crop plants

• We need to shift the

balance of power

away from the weed

and to the crop

Annual Weed Success: Why Do Weeds Win?

• Annual weeds make lots of seed, resulting in many individual weeds occurring at the same time

• Even if only one weed/ft2 survives out of perhaps 100 seedlings/ft2, it can replenish the seed bank in a single season

Understanding Germination of Weed Seeds

Seeds respond to light using phytochrome

Understanding Germination of Weed Seeds

Seeds respond to light using phytochrome

Understanding Germination of Weed Seeds

Seeds respond to light using phytochrome

Red light exposure

activates

phytochrome, so

seeds may germinate

Understanding Germination of Weed Seeds

Seeds respond to light using phytochrome

Far red light exposure

inactivates

phytochrome, so

seeds don’t germinate

Understanding Germination of Weed Seeds

• Seeds near or on the soil surface gain red light exposure and germinate

• Deeply-buried weed seeds are not exposed to light (or are exposed to far-red radiation), so they usually do not germinate

Seeds Respond to Light

Understanding Germination of Weed Seeds

• Winter annuals typically germinate under short-day radiation

• Summer annuals typically germinate when days are lengthening in the spring

Seeds Respond to Light

Understanding Germination of Weed Seeds

• Winter annuals germinate in cool soil

• Summer annuals germinate in warming soil, often after a period of exposure to cold temperatures

Seeds Respond to Temperature

Understanding Germination of Weed Seeds

Seeds Respond to Moisture

• Seeds must be imbibed prior to germination

• Many species require a stratification process to leach chemicals from the seed and allow dormancy to break

Annual Weed Success

Every cultivation brings buried seed to the soil surface where they can germinate

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts

0

2000

4000

6000

8000

10000

Fall Spring Total

Com + Bas

Sen (Hi, PRE)

Com (Hi)

Com + Sen (PRE)

Com + Sen (PRE,POST)

Untreated

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts

0

2000

4000

6000

8000

10000

Fall Spring Total

Com + Bas

Sen (Hi, PRE)

Com (Hi)

Com + Sen (PRE)

Com + Sen (PRE,POST)

Untreated

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts

0

2000

4000

6000

8000

10000

Fall Spring Total

Com + Bas

Sen (Hi, PRE)

Com (Hi)

Com + Sen (PRE)

Com + Sen (PRE,POST)

Untreated

Reduced Rate Herbicide Trial—Total Weed Seed Germination Counts

0

2000

4000

6000

8000

10000

Fall Spring Total

Com + Bas

Sen (Hi, PRE)

Com (Hi)

Com + Sen (PRE)

Com + Sen (PRE,POST)

Untreated

• So in this case, return of weed seed to

field would have resulted in:

– Command + Basagran (PRE + POST)

• 3 weeds/m2 (12,000/acre)

– Sencor (PRE)

• 469 weeds/m2 (1.9 million/acre)

– Untreated check

• 8055 weeds/m2 (32.6 million/acre)

Weed Seed Germination

Vegetative Reproduction

• Roots

• Rhizomes

• Stolons

Vegetative Reproduction

• Roots

• Rhizomes

• Stolons

Vegetative Reproduction

• Roots

• Rhizomes

• Stolons

Vegetative Reproduction

•Bulbs

•Tubers

•Rooting

at nodes

Vegetative Reproduction

•Bulbs

•Tubers

•Rooting

at nodes

Vegetative Reproduction

•Bulbs

•Tubers

•Rooting

at nodes

Vegetative Reproduction

Why Does VR Make Sense for Plants?

• Only small portions of vegetative structures are needed for the plant to successfully reproduce

– Sections as small as ¼-inch of a Canada thistle root is sufficient to start a new infestation

– Stem sections only 2 inches long are enough to start a new infestation of Bohemian knotweed

– A single daughter plant crown of creeping buttercup is sufficient to start a new infestation

– Three or more shoots can arise from a single yellow nutsedge tuber

Vegetative Reproduction

Why Does VR Make Sense for Plants?

• Shoots from VR structures have access to

more energy than do seedlings

– They usually grow faster and capture

space more quickly than plants arising

from seeds

• Plants from VR structures are already well-

suited to the environment, having come

from a successfully adapted plant

Vegetative Reproduction

Why Does VR Make Sense for Plants?

• On plants that vegetatively reproduce

themselves, there are usually many shoots

from a single root system

– Controlling the plant means killing not

only all those individual shoots, but also

all the roots that are attached to those

multiple shoots (a difficult task!)

The Next Weed Session Session 1: Biology of Weeds

Session 2: Weed Reproduction

Session 3: Non-chemical Weed Management

Session 4: Chemical Weed Management