session 2: weed reproduction… · session 2: weed reproduction . ... from seeds •plants from vr...
TRANSCRIPT
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