Weeds L3 Flashcards
Weed biology
part of weed science devoted to the study of the growth, development, and reproduction of weeds
Why do we need weed biology
essential for developing effective control methods
need to identify weed to control it
allows us to minimize negative effects
most effect weed control methods are based on the _____ _______
life cycle
control methods vary depending on:
weeds species, crop, field situation, environmental conditions
Aspects of weed biology that affect weed management
life stages/cycles
emergence periods
fecundity (seed production)
seed longevity
risk of developing herbicide resistance
What 2 parts indicate the potential weed problem
seed longevity and seed production
4 stages of weed development
seedling
vegetative
seed production
maturity
seedling stage
small, delicate, newly emerged plants
vegetative stage
fast growth; production of stems, roots, and leaves
seed production stage
energy is directed towards seed production
maturity
seed shed and plant death
seeds vs. seedlings
Seeds are not easy to detect but seedlings are
seeds can disperse easily, but seedlings cant move
Seeds can persist in soil but seedlings are weak/die easily
Seeds are physically and chemically defended but seedling are vulnerable
Types of weed reproducton
Sexual (seeds)
asexual (specialized vegetative structures
asexual seeds (apomixis)
sexual reprodcution
requires fertilization of an egg by sperm to produce chance for genetic change
can vary greatly among and within weed species
(less important for perennials)
Weeds generally produce _____ seeds than crops
more
Example of genetic change in weeds
herbicide resistance
Asexual reproduction via seeds
apomixis which uses no miosis or fertilization. Apomixis seeds are genetic clones of their mothers
examples of weeds reproducing via apomixis
hawkweed, dandelion
how many angiosperms can reproduce via apomixis
over 400 (most can also reproduce sexually)
Asexual reproduction via specialized vegetative structure
new plant develops from a modified stem, root, or leaf
common in perennial and can be just as successful as seeds
examples of vegetative structures
rhizomes (underground stems)
stolons/runners (above-ground stems)
bulbs, corms, and tubers
vegetative reproduction weed example
common chickweed (stolon)
Canada thistle (rhizomes)
nutsedge (tubers)
benefits of dispersal for the weed
colonization of new or more suitable habitat
reduction of parent-offspring competition
make sure offspring are spread out to avoid attracting predators (Jazen-Connell hypothesis)
reduction in inbreeding
Dispersal by wind
weed seeds and fruits that disseminate through wind that have special organs to keep them afloat
pappus
a parachute-like modification of the calyx into hairs
Ex: dandelion, hairy fleabane
calyx
all the sepals
comose
hair that cover the seed partially or fully
Ex: crown flower
feathery persistent styles
styles are persistent and feathery
Ex: tall thimbleweed
balloon
calyx is modified into a papery structure enclosing fruit along with entrapped air
wings
one or more appendages that act as wings
ex: bigleaf maple
Wind dispersion modifications
pappus, comose, feathery persistent styles, balloon, wings
factors that affect wind dispersal
seed weight and shape
height of release
wind speed and turbulence
seed structures
Dispersal by water
disperse through water (irrigation and waterways) and remain viable for several years
Example of water dispersal modification
curly dock seeds with pontoons
dispersal by animals
Animals carry seeds on skin, hair, hooves, or through their digestive systems
Animal dispersal modifications
barbs, hooks, spines, rasps
Types of weed dispersal
wind, water, animal, human, machinery, crop mimicry, contaminants
dispersal by man
often spread though agriculture
satellite weeds
weeds that mature at the same time and height as the crop that look very similar in shape and size. Man would unknowingly harvest the weed and assist in its dispersal
examples of satellite weeds
Wild oat
little seed canarygrass
dispersal by machinery
seeds dispersed by tillage and harvesting equipment
crop mimicry dispersal
weed seeds adapted to look like crop seed
examples of crop mimicry dispersal
Nightshade fruits - look like dry beans
common vetch - looks like lentil
barnyard grass - plant looks like rice and escapes hand weeding
Dispersal as contaminants
can contaminate crop seed, animal feed and hay/straw
favorable conditions for weed seed germination
light exposure
aerobic conditions
available essential nutrients (nitrate sensing)
correct soil temp and moisture
empty site or niches are often associated with ___________
canopy gaps
How do weed seeds sense presence of empty gaps
seed embryo contains photo-sensitive pigments (light sensors) that can sense the presence of an open space
gap sensing
can sense no gap (low light intensity and quality) and a gap (higher light intensity and quality)
germination timing
photo-sensitive pigments in seed sense day length and night duration to enable germination periodicity
What is seed dormancy
a state of seeds in which they are alive but not germinated
reasons seeds can remain dormant
enforced dormancy
induced dormancy
innate dormancy
Enforced dormancy
seed buried deeper than 5cm. They will germinate when brought to top soil layer.
induced dormancy
due to physiological changes in otherwise non-dormant seed. Could be due to rise in soil temp and CO2 levels, low O2 level in soil, overcrowding or water logging)
Innate dormancy
Due to genetic factors often specific to a species. Could be due to immature embryos, hard seed coats, presence of germination inhibitors in seed (abscisic acid)
Seed species can exhibit ____types of seed dormancy
more than 1
Can vegetative structures also exhibit dormancy?
Yes (in some species)
Types of soil seed banks based on longevity
transient seed bank and persistent seed bank
Transient seed bank
species whose seed live in soil for less than a year
persistent seed bank
species whose seed live in the soil for a year or greater
