Weeds L3

Question 1

Weed biology

Answer 1

part of weed science devoted to the study of the growth, development, and reproduction of weeds

Question 2

Why do we need weed biology

Answer 2

essential for developing effective control methods
need to identify weed to control it
allows us to minimize negative effects

Question 3

most effect weed control methods are based on the _____ _______

Answer 3

life cycle

Question 4

control methods vary depending on:

Answer 4

weeds species, crop, field situation, environmental conditions

Question 5

Aspects of weed biology that affect weed management

Answer 5

life stages/cycles
emergence periods
fecundity (seed production)
seed longevity
risk of developing herbicide resistance

Question 6

What 2 parts indicate the potential weed problem

Answer 6

seed longevity and seed production

Question 7

4 stages of weed development

Answer 7

seedling
vegetative
seed production
maturity

Question 8

seedling stage

Answer 8

small, delicate, newly emerged plants

Question 9

vegetative stage

Answer 9

fast growth; production of stems, roots, and leaves

Question 10

seed production stage

Answer 10

energy is directed towards seed production

Question 11

maturity

Answer 11

seed shed and plant death

Question 12

seeds vs. seedlings

Answer 12

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

Question 13

Types of weed reproducton

Answer 13

Sexual (seeds)
asexual (specialized vegetative structures
asexual seeds (apomixis)

Question 14

sexual reprodcution

Answer 14

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)

Question 15

Weeds generally produce _____ seeds than crops

Answer 15

more

Question 16

Example of genetic change in weeds

Answer 16

herbicide resistance

Question 17

Asexual reproduction via seeds

Answer 17

apomixis which uses no miosis or fertilization. Apomixis seeds are genetic clones of their mothers

Question 18

examples of weeds reproducing via apomixis

Answer 18

hawkweed, dandelion

Question 19

how many angiosperms can reproduce via apomixis

Answer 19

over 400 (most can also reproduce sexually)

Question 20

Asexual reproduction via specialized vegetative structure

Answer 20

new plant develops from a modified stem, root, or leaf
common in perennial and can be just as successful as seeds

Question 21

examples of vegetative structures

Answer 21

rhizomes (underground stems)
stolons/runners (above-ground stems)
bulbs, corms, and tubers

Question 22

vegetative reproduction weed example

Answer 22

common chickweed (stolon)
Canada thistle (rhizomes)
nutsedge (tubers)

Question 23

benefits of dispersal for the weed

Answer 23

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

Question 24

Dispersal by wind

Answer 24

weed seeds and fruits that disseminate through wind that have special organs to keep them afloat

Question 25

pappus

Answer 25

a parachute-like modification of the calyx into hairs Ex: dandelion, hairy fleabane

Question 26

calyx

Answer 26

all the sepals

Question 27

comose

Answer 27

hair that cover the seed partially or fully Ex: crown flower

Question 28

feathery persistent styles

Answer 28

styles are persistent and feathery Ex: tall thimbleweed

Question 29

balloon

Answer 29

calyx is modified into a papery structure enclosing fruit along with entrapped air

Question 30

wings

Answer 30

one or more appendages that act as wings ex: bigleaf maple

Question 31

Wind dispersion modifications

Answer 31

pappus, comose, feathery persistent styles, balloon, wings

Question 32

factors that affect wind dispersal

Answer 32

seed weight and shape height of release wind speed and turbulence seed structures

Question 33

Dispersal by water

Answer 33

disperse through water (irrigation and waterways) and remain viable for several years

Question 34

Example of water dispersal modification

Answer 34

curly dock seeds with pontoons

Question 35

dispersal by animals

Answer 35

Animals carry seeds on skin, hair, hooves, or through their digestive systems

Question 36

Animal dispersal modifications

Answer 36

barbs, hooks, spines, rasps

Question 37

Types of weed dispersal

Answer 37

wind, water, animal, human, machinery, crop mimicry, contaminants

Question 38

dispersal by man

Answer 38

often spread though agriculture

Question 39

satellite weeds

Answer 39

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

Question 40

examples of satellite weeds

Answer 40

Wild oat little seed canarygrass

Question 41

dispersal by machinery

Answer 41

seeds dispersed by tillage and harvesting equipment

Question 42

crop mimicry dispersal

Answer 42

weed seeds adapted to look like crop seed

Question 43

examples of crop mimicry dispersal

Answer 43

Nightshade fruits - look like dry beans common vetch - looks like lentil barnyard grass - plant looks like rice and escapes hand weeding

Question 44

Dispersal as contaminants

Answer 44

can contaminate crop seed, animal feed and hay/straw

Question 45

favorable conditions for weed seed germination

Answer 45

light exposure aerobic conditions available essential nutrients (nitrate sensing) correct soil temp and moisture

Question 46

empty site or niches are often associated with ___________

Answer 46

canopy gaps

Question 47

How do weed seeds sense presence of empty gaps

Answer 47

seed embryo contains photo-sensitive pigments (light sensors) that can sense the presence of an open space

Question 48

gap sensing

Answer 48

can sense no gap (low light intensity and quality) and a gap (higher light intensity and quality)

Question 49

germination timing

Answer 49

photo-sensitive pigments in seed sense day length and night duration to enable germination periodicity

Question 50

What is seed dormancy

Answer 50

a state of seeds in which they are alive but not germinated

Question 51

reasons seeds can remain dormant

Answer 51

enforced dormancy induced dormancy innate dormancy

Question 52

Enforced dormancy

Answer 52

seed buried deeper than 5cm. They will germinate when brought to top soil layer.

Question 53

induced dormancy

Answer 53

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)

Question 54

Innate dormancy

Answer 54

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)

Question 55

Seed species can exhibit ____types of seed dormancy

Answer 55

more than 1

Question 56

Can vegetative structures also exhibit dormancy?

Answer 56

Yes (in some species)

Question 57

Types of soil seed banks based on longevity

Answer 57

transient seed bank and persistent seed bank

Question 58

Transient seed bank

Answer 58

species whose seed live in soil for less than a year

Question 59

persistent seed bank

Answer 59

species whose seed live in the soil for a year or greater