Lecture 2: Biology of weeds

Question 1

the world population is predictive to reach __ by 2050

Answer 1

9 billion

Question 2

more than ____ people of not have adequate food

Answer 2

800 million

Question 3

___ people live on less than $1 a day

Answer 3

1.3 billion

Question 4

At least ___% of global food production is lost pre-harvest to weeds, pests & diseases in developed countries

Answer 4

30%

- this rises to 40-50% for some crops in the developed world

Question 5

weeds, pests, and diseases are a __ to food security

Answer 5

THREAT

Question 6

Weed control examples:

Answer 6

• cultivation practices
• biological control
• chemical control
• biotech solutions
• plant breeding strategies
• integrated control strategies

Question 7

cultivation practises e.g.:

Answer 7

good drainage, manuring + liming, choice of crop and varieties, rotation of crops, weeding & good farm hygiene

Question 8

biotech solutions to weed control e.g.

Answer 8

genetic modification of crops

Question 9

plant breeding strategies to weed control e.g.

Answer 9

resistant cultivars

Question 10

2 definitions of a weed:

Answer 10

“a plant growing in any situation where it is considered to be undesirable”

” A plant growing in the wrong place at the wrong time”

Question 11

can weeds be both monocotyledonous and dicotyledonous plants??

Answer 11

YES,

can be broad leaved dicotyledonous plants or monocotyledonous e.g. grasses

Question 12

is a weed always a weed?

Answer 12

no, a plant may be a weed in some circumstances but not in others

Question 13

of the 250,000 plant species in the world only ____ are troublesome weeds

Answer 13

only a few hundred

Question 14

plants classified as agricultural weeds possess

Answer 14

certain characteristics which contribute to their success

Question 15

biological characteristics commonly possessed by weedy species:

Answer 15

• Competitiveness

- Persisitence

Question 16

competitiveness in weeds:

Answer 16

is the ability of weeds to draw resources (light, water, nutrients and CO2) away from crop plants

Question 17

persistence in weeds:

Answer 17

the ability to survive from year to year on a given area of land despite farmers attempts to control them

Question 18

traits contributing to competitiveness and persistence in weeds include:

Answer 18

• rapid seedling establishment
• high growth rates
• prolific root systems
• large leaf area
• high reproductive output
• plasticity (the ability to adapt to changes in the environment)
• type of life cycle to the crop
• germination characteristic of seeds

Question 19

life cycle of weeds: Annuals:

Answer 19

complete their life cycle in one season e.g. poppies, nettles, thistles

Question 20

life cycle of weeds: biennials:

Answer 20

take two years to complete their life cycles e.g. ragwort

Question 21

life cycle of weeds:

Answer 21

• Annual
• biennials
• ephermerals
• perennials

Question 22

life cycle of weeds: Ephermerals:

Answer 22

produce several generations of seed per year e.g. hairy bittercress & chickweed

Question 23

life cycle of weeds: perennials:

Answer 23

• persists from year to year

- the aerial shoots die back & plants persist vegetatively as stolons, rhizomes, bulbs or tap roots

Question 24

Perennials: Coltsfoot

Answer 24

persists by means of underground rhizomes

Question 25

perennials: creeping buttercup

Answer 25

persists by means of stolons, underground stems

Question 26

perennials: wild garlic and wild onion

Answer 26

persist by means of a bulb

Question 27

understanding there germination characteristics of weed species is important for

Answer 27

weed control

Question 28

all agricultural soils have ___ seed banks

Answer 28

LARGE

Question 29

things to understand of the large seed banks in agricultural soils

Answer 29

- depth of germination - -> most seed have amax depth from which they can germinate depending on seed size and food reserves - -> the majority of annual seeds are to be found in the top 5cm of soil - periodicity of germination - dormancy

Question 30

periodicity of germination:

Answer 30

- most seeds of a given weed species germinate & emerge at a particular time of the year - means there is a close association between certain weed sp. and certain crop plants - maximum period of germination is known then correct herbicide can be chosen

Question 31

periodicity of germination: Ive leaved speedwell

Answer 31

germinates in the autumn and winter and is a problem in winter cereals

Question 32

periodicity of germination: Chickweed

Answer 32

emerges in the spring and is a problem in spring and summer crops

Question 33

dormancy is a mechanism that

Answer 33

has evolved to ensure survival of the species. Most seed have primary or innate dormancy when they are direct produced

Question 34

primary or innate dormancy may be due to:

Answer 34

- impermeability of the seed coat to water - impermeability of the seed coat to gases - mechanical resistance to embryo growth - immaturity of the embryo - the embryo may require a period of drying or cold

Question 35

how do weeds damage crops?

Answer 35

- competition for resources - loss in the quality of produce - poisoning of livestock - harbouring of pests & diseases - pollination

Question 36

how do weeds damage crops? competition or resources & | are most weeds parasitic?

Answer 36

- competition for resources (light, water, CO2, nutrients) - -most weeds are not parasitic on their hosts & compete, indirectly for resources. Few are parasitic on crop species & Compete for host resources directly

Question 37

the effect of weed density on rice yields:

Answer 37

- as weed density increases, the yield of cultivated rice decreases - the extent of the decrease in yield differs depending upon the weed - the field decrease occurs as a result of competition for, water & sometimes light

Question 38

competition for water:

Answer 38

those plants outcompeted for water are a lot smaller and lack growth

Question 39

where are parasitic weeds important?

Answer 39

- sub Saharan Africa e.g. Strega species | - some Mediterranean agro-ecosystems e.g. Orobanche species

Question 40

how do parasitic weeds lower yield:

Answer 40

-Directly compete with the host for host resources (e.g. carbon, nitrogen and inorganic solutes) as they parasitise the host

Question 41

Striga species not only parasitise their host but cause

Answer 41

a molecular reprogramming of host development

Question 42

example of 2 root parasites:

Answer 42

- Orobanche cumana (broomrape) (obligate holoparasite) | - Striga hermonthica (witchweed) (obligate hemiparasite)

Question 43

Striga hermonthica & S. asiatica infect:

Answer 43

Maize, sorghum, millet & upland rice directly affecting the lives of 100M people in sub Saharan Africa

Question 44

___ ha land infested with Striga seed & yield losses of ___% are common

Answer 44

- 70M ha | - 40-100%

Question 45

Orobanche species infect

Answer 45

many legumes & vegetables & Crops such as sunflower, tomato & tobacco

Question 46

where are Orobanche species a problem & how much loss do they cause:

Answer 46

problem in Russia, Ukraine, Mediterranean regions, North Africa & the middle east again causing losses form 10-100%

Question 47

control of parasitic weed is ___

Answer 47

very difficult

Question 48

Effects of Striga on the host:

Answer 48

1) lowers biomass and height 2) Reduction in biomass & grain production due to: - -utilisation of host nutrients by the parasite (competition) - -Molecular reprogramming of host growth & development

Question 49

the genus Orobanche includes more than

Answer 49

100 species

Question 50

distribution of orobanche:

Answer 50

mainly in the mediterranean Basin, but also in Eastern Europe, Former Soviet Union

Question 51

which genus are holoparasitic and what does this mean

Answer 51

OROBANCHE, lacks chlorophyll

Question 52

does Orobanche form direct connections with the host phloem & xylem

Answer 52

YES

Question 53

how does orobanche lower the yield of host

Answer 53

by acting as a very efficient sink for host carbon, nitrogen & inorganic nutrients

Question 54

five species of orobanche for economic important

Answer 54

``` O. aegyptiaca O. ramosa O. cumana O. cernua O. Crenata ```

Question 55

Orobanche parasitised cultivated species:

Answer 55

sunflower, cabbage, cucumber, potato, tomato, tobacco, carrot

Question 56

__ ha infected with O. cumana

Answer 56

73 million hectares infested with O. cumana

Question 57

Orabanche can lead up to yield losses of up to

Answer 57

50%

Question 58

existing management methods have ___ against Orobanche

Answer 58

limited success & applicability

Question 59

how do weeds damage crops? loss in the quality of produce

Answer 59

1. Contamination of produce for processing e.g. • Wild oats in malting barley • Black nightshade berries in peas 2. Weed seeds are an impurity in crop seed which can lead to failure to reach EEC standards 3. Harvesting problems • The presence of weeds in a crop slows down combine harvesters • If the weed ripens after the cereal it may raise the moisture content of the grain h increasing drying costs.

Question 60

how do weeds damage crops? Poisoning of livestock

Answer 60

* Many common weeds are poisonous to livestock e.g. ragwort, bracken and hemlock. * Most cattle will avoid these species in the field but the real problem come if they get into silage. * Horses and cows are more susceptible to ragwort poisoning than other livestock. * Young animals are even more susceptible than older animals. * Ragwort destroys the liver of the animal by poisoning. * Little can be done after clinical symptoms appear.

Question 61

how do weeds damage crops? harbouring of pests & diseases

Answer 61

• Weeds may be a problem if they harbour pests and disease of crops. • Several weed species act as a host for a range of fungal, viral and nematode borne diseases e.g. – Couch grass/Take-All of wheat – Chickweed/nematodes.

Question 62

how do weeds damage crops? Pollination

Answer 62

* Weeds can compete with trees in orchards for pollination by bees. * The flowers of some weeds attract bees more than apple and plum blossom. * Weeds in orchards also reduce yield by competing for water and nutrients

Question 63

3 approaches to weed management:

Answer 63

- prevention - Eradication - control

Question 64

prevention aim:

Answer 64

is to keep weed seeds & vegetative materials from being introduced into a field e.g. --• Make sure that seed that is sown is pure • Clean implements when moving from one field to another • Mow weeds in field borders to prevent seed se

Question 65

Eradication: because weeds are persistent once they become established it is _____ to eradicate them

Answer 65

is almost impossible and impractical

Question 66

Eradication is ___ attempted

Answer 66

RARELY | and is only considered when a noxious weed has been inadvertently introduced from one area to another.

Question 67

a successful eradication programme requires:

Answer 67

a long term connected effort consisting of several preventative & Control measures e.g. the attempt to eliminate Striga from the USA