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PLSC 260 > Weeds L3 > Flashcards

Weeds L3 Flashcards

1
Q

Weed biology

A

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

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2
Q

Why do we need weed biology

A

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

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3
Q

most effect weed control methods are based on the _____ _______

A

life cycle

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4
Q

control methods vary depending on:

A

weeds species, crop, field situation, environmental conditions

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5
Q

Aspects of weed biology that affect weed management

A

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

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6
Q

What 2 parts indicate the potential weed problem

A

seed longevity and seed production

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7
Q

4 stages of weed development

A

seedling
vegetative
seed production
maturity

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8
Q

seedling stage

A

small, delicate, newly emerged plants

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9
Q

vegetative stage

A

fast growth; production of stems, roots, and leaves

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10
Q

seed production stage

A

energy is directed towards seed production

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11
Q

maturity

A

seed shed and plant death

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12
Q

seeds vs. seedlings

A

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

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13
Q

Types of weed reproducton

A

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

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14
Q

sexual reprodcution

A

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)

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15
Q

Weeds generally produce _____ seeds than crops

A

more

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16
Q

Example of genetic change in weeds

A

herbicide resistance

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17
Q

Asexual reproduction via seeds

A

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

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18
Q

examples of weeds reproducing via apomixis

A

hawkweed, dandelion

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19
Q

how many angiosperms can reproduce via apomixis

A

over 400 (most can also reproduce sexually)

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20
Q

Asexual reproduction via specialized vegetative structure

A

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

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21
Q

examples of vegetative structures

A

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

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22
Q

vegetative reproduction weed example

A

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

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23
Q

benefits of dispersal for the weed

A

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

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24
Q

Dispersal by wind

A

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

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25
Q

pappus

A

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

26
Q

calyx

A

all the sepals

27
Q

comose

A

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

28
Q

feathery persistent styles

A

styles are persistent and feathery
Ex: tall thimbleweed

29
Q

balloon

A

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

30
Q

wings

A

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

31
Q

Wind dispersion modifications

A

pappus, comose, feathery persistent styles, balloon, wings

32
Q

factors that affect wind dispersal

A

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

33
Q

Dispersal by water

A

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

34
Q

Example of water dispersal modification

A

curly dock seeds with pontoons

35
Q

dispersal by animals

A

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

36
Q

Animal dispersal modifications

A

barbs, hooks, spines, rasps

37
Q

Types of weed dispersal

A

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

38
Q

dispersal by man

A

often spread though agriculture

39
Q

satellite weeds

A

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

40
Q

examples of satellite weeds

A

Wild oat
little seed canarygrass

41
Q

dispersal by machinery

A

seeds dispersed by tillage and harvesting equipment

42
Q

crop mimicry dispersal

A

weed seeds adapted to look like crop seed

43
Q

examples of crop mimicry dispersal

A

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

44
Q

Dispersal as contaminants

A

can contaminate crop seed, animal feed and hay/straw

45
Q

favorable conditions for weed seed germination

A

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

46
Q

empty site or niches are often associated with ___________

A

canopy gaps

47
Q

How do weed seeds sense presence of empty gaps

A

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

48
Q

gap sensing

A

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

49
Q

germination timing

A

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

50
Q

What is seed dormancy

A

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

51
Q

reasons seeds can remain dormant

A

enforced dormancy
induced dormancy
innate dormancy

52
Q

Enforced dormancy

A

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

53
Q

induced dormancy

A

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)

54
Q

Innate dormancy

A

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)

55
Q

Seed species can exhibit ____types of seed dormancy

A

more than 1

56
Q

Can vegetative structures also exhibit dormancy?

A

Yes (in some species)

57
Q

Types of soil seed banks based on longevity

A

transient seed bank and persistent seed bank

58
Q

Transient seed bank

A

species whose seed live in soil for less than a year

59
Q

persistent seed bank

A

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

60
Q
A

PLSC 260 (14 decks)

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