Cereals Week 10 2024 Weed Control Part 1

Question 1

Why do we control weeds in crop production?

Answer 1

• 1. To reduce the competition effect
• 2. Allow ease of harvesting
• 3. Achieve high grain (seed) quality
• 4. To prevent the build-up of problem weeds

Question 2

What is a weed?

Answer 2

A weed can be any plant growing in the wrong place

Question 3

What are huge problems in crop rotations?

Answer 3

In crop rotations volunteer weeds are big problems
e.g. potatoes growing in a cereal crop, or
wheat/barley growing in a bean crop etc

Question 4

What are 2 effects of weeds?

Answer 4

• 1. Competitive effect :
     Crop Yield
• 2. Ease of harvesting :
     Grain
     quality

Question 5

What are the 3 weed types?

Answer 5

– a. grass weeds
– b. annual broad leaved weeds
– c. perennial broad-leaved weeds

Question 6

What are key competitive weeds?

Answer 6

cleavers, wild oats, and strong grasses

Question 7

Name 2 non chemical methods of weed control?

Answer 7

• Cultural methods
• Cultivation practices

Question 8

What are 4 cultural methods for weed control?

Answer 8

– Winter cropping and spring cropping
– Rotations : use of break crops / root crops / grass
– also fallow (set-aside)
– Cover crop options

Question 9

What are the 3 cultivation practices for non-chemical weed control?

Answer 9

– Ploughing to invert soil and bury weed problems giving
80/90% weed control for certain grassweed species
– Minimum tillage with stale seedbed sequences
– Stubble cultivation

Question 10

Are cultivations negative or positive effects?

Answer 10

Cultivations can have negative and positive effects

Question 11

What can weeds sometimes have ? why can they be stubborn?

Answer 11

Dormancy , they be stubborn and they wont grow

Question 12

What are the 3 methods of weed control?

Answer 12

-Mechanical
-Hand
-Chemical

Question 13

What are mechanical methods of weed control? (2)

Answer 13

– Topping of weeds (grassland / set-aside)

– In growing crop its usually used as localised control of
problem weeds (strimming)

Question 14

What is Hand roughing for weed control methods?

Answer 14

– Roughing of wild oats

– Very commonly used in parts of the world where farms
are small and /or labour is cheap as a cost-effective
alternative to expensive herbicides

Question 15

How much chemicals do field crops tend to get?

Answer 15

– field crops tend to get at least one herbicide application on
the growing crop

Question 16

How much chemical weed control do cereal crops have?
Whats used on them?

Answer 16

– in cereal crops usually 2 or more a.i.’s are applied in a
single application

• either as a tank-mix, e.g. Ally + CMPP
• or as a formulated product, e.g. DFF + IPU

Question 17

How much chemical is complete “between” crops ?

Answer 17

– Pre-harvest is commonly used on many crops / sometimes
as a dessicant (oilseeds/potatoes)

– On stubble etc glyphosate is widely used

Question 18

Growing different crops are planned in what sort of a sequence?

Answer 18

• Growing different crops in a planned sequence
  across a farm area over a period of time (3-6/8 years)

Question 19

What are weed control advantages? (2)

Answer 19

–flexibility of sowing date – winter/spring

–cultivation method– root crop

Question 20

What are the 2 opportunities for different chemical weed control strategies?

Answer 20

– - herbicides with different modes of action/spectrum

– - pre-emergence and post-emergence options

Question 21

Do all weeds germinate all year round?

Answer 21

No not all weeds germinate all year round.

Polygonum weeds are spring germinating only

Question 22

List the 4 important weed groups :

Answer 22

1* Annual grass weeds
– meadowgrass’s / ryegrass’s

2* Perennial grass weeds
– scutch (couch) / creeping bent/soft grass

3* Annual broad-leaved weeds
– chickweed / cleavers / fat hen / charlock etc

4* Perennial broad-leaved weeds
– docks / thistles / creeping buttercup

Question 23

List Annual Grass weed groups? (2)

Answer 23

Meadowgrass’s / ryegrass’s

Question 24

Lst 2 Perennial grass weeds?

Answer 24

– scutch (couch) / creeping bent/soft grass

Question 25

List 4 Annual Broad leaved weeds:

Answer 25

– chickweed / cleavers / fat hen / charlock etc

Question 26

List 3 Perennial Broad -Leaved weeds:

Answer 26

– docks / thistles / creeping buttercup

Question 27

Annual Meadowgrass: Poa Annua
1- How many types of Poa species is there?
2- Out of all of these how many of them are arable weeds?
3- When does it germinate?
4-Is flowering independent or dependent?
5- How many seeds per inflorescence?
60 how many seeds are to be produced in an average of 2050 seeds per plant?
6- How long does seed remain viable for?

Answer 27

1- 15 types of Poa species, of
which 3 are arable weeds.
2- P. Annua is a very adaptable
spp. with many known
ecotypes
3- Germinates from Feb to
November with little
dormancy.
4- Flowering is independent of
day length and will occur
throughout the year.
5- Abundant seed producer. 80
seeds per inflorescence. Said
to produce an average of
2050 seeds per plant.
6- Seed remains viable in the
soil for up to 4 years

Question 28

What is chemical weed control in cereals: herbicide use a function of?

Answer 28

– resistance of crop to herbicide

– susceptibility of the weeds to herbicide

Question 29

What does the resistance of the crop depend on? (3)

Answer 29

– type of crop and growth stage
– health and vigour of the crop
– dosage and correct application

Question 30

What does the susceptibility of weeds depend on? (4)

Answer 30

– type of weeds and stage of growth
– condition of weed growth
– weather at spraying
– interaction with tank mix chemicals

Question 31

Urea Herbicides MOA: (4)

Answer 31

Urea derivatives / IPU , Linuron, Methabenzthiazuron

Question 32

Amides MOA:

Answer 32

Propyzamide

Question 33

Nitriles MOA: (2)

Answer 33

HBN’s and Casoron

Question 34

Triazines MOA : (3)

Answer 34

very soil persistent (simazine / atrazine / terbutryne)

Question 35

Carbamates MOA(2):

Answer 35

– CIPC / IPC (Propham) phenmedipham (Betanal) , asulox

Question 36

Anilides / Nitroanilines MOA (3):

Answer 36

Inhibitors / Metazachlor , diflufenican , pendimethalin

Question 37

Thiocarbamates MOA:

Answer 37

Avadex

Question 38

Organophosphorus MOA: (2)

Answer 38

Glyphosate , glufosinate

Question 39

Sulphonyl Ureas MOA:

Answer 39

– Many, many products on market

Question 40

Phenoxy Alkanoic acids: MOA

Answer 40

– Fops and Dins ( Fluazifop / Fenoxaprop etc )

Question 41

Hormonal type herbicides: MOA

Answer 41

– Alkanoic acids
– Arylcarboxylic acids (derivatives)
– Urea herbicides

Question 42

1- What’s herbicide group 1?

2- What sort of Amino Acids are being used?

3- What’s the site of action group 2?

4- What are plant injury symptoms?

Answer 42

1- Sulphonyl Ureas

2- Amino Acid Synthesis Inhibitors; Branch Chain Amino Acid Inhibitors

3- Site of Action Group 2 - Inhibitors of acetolactase synthase (ALS)
and also called acetohydroxyacid synthase (AHAS)

4- midazolinones (phloem mobile)
Also referred to as “imi” herbicides. Grass plants may be stunted
with interveinal yellowing (chlorosis) or purpling.

Question 43

When choosing herbicides whats the 4 important things to remember:

Answer 43

1- select products which are safe on the crop

2- select products usable at the relevant GS’s

3- select a product to best control the most
difficult weed problems

4- look at alternatives to the product chosen in the
light of : – cost/ha, toxicity, nature of use

Question 44

One years weed is …

Answer 44

7 years seed

Question 45

What sort of weeds will seed before harvest?

Answer 45

Many weeds like wild
oats and sterile brome
will seed before
harvest

the large seed bank
then returned to the
soil become weeds for
many future years

Question 46

Whats a problem in Min-Till systems?

Answer 46

Widespread problems in mintil systems= Sterile Brome Control