Cereals Week 10 2024 Weed Control Part 1 Flashcards
Why do we control weeds in crop production?
- To reduce the competition effect
- Allow ease of harvesting
- Achieve high grain (seed) quality
- To prevent the build-up of problem weeds
What is a weed?
A weed can be any plant growing in the wrong place
What are huge problems in crop rotations?
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
What are 2 effects of weeds?
- Competitive effect :
Crop Yield
- Competitive effect :
- Ease of harvesting :
Grain
quality
- Ease of harvesting :
What are the 3 weed types?
– a. grass weeds
– b. annual broad leaved weeds
– c. perennial broad-leaved weeds
What are key competitive weeds?
cleavers, wild oats, and strong grasses
Name 2 non chemical methods of weed control?
- Cultural methods
- Cultivation practices
What are 4 cultural methods for weed control?
– Winter cropping and spring cropping
– Rotations : use of break crops / root crops / grass
– also fallow (set-aside)
– Cover crop options
What are the 3 cultivation practices for non-chemical weed control?
– 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
Are cultivations negative or positive effects?
Cultivations can have negative and positive effects
What can weeds sometimes have ? why can they be stubborn?
Dormancy , they be stubborn and they wont grow
What are the 3 methods of weed control?
-Mechanical
-Hand
-Chemical
What are mechanical methods of weed control? (2)
– Topping of weeds (grassland / set-aside)
– In growing crop its usually used as localised control of
problem weeds (strimming)
What is Hand roughing for weed control methods?
– 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
How much chemicals do field crops tend to get?
– field crops tend to get at least one herbicide application on
the growing crop
How much chemical weed control do cereal crops have?
Whats used on them?
– 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
How much chemical is complete “between” crops ?
– Pre-harvest is commonly used on many crops / sometimes
as a dessicant (oilseeds/potatoes)
– On stubble etc glyphosate is widely used
Growing different crops are planned in what sort of a sequence?
- Growing different crops in a planned sequence
across a farm area over a period of time (3-6/8 years)
What are weed control advantages? (2)
–flexibility of sowing date – winter/spring
–cultivation method– root crop
What are the 2 opportunities for different chemical weed control strategies?
– - herbicides with different modes of action/spectrum
– - pre-emergence and post-emergence options
Do all weeds germinate all year round?
No not all weeds germinate all year round.
Polygonum weeds are spring germinating only
List the 4 important weed groups :
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
List Annual Grass weed groups? (2)
Meadowgrass’s / ryegrass’s
Lst 2 Perennial grass weeds?
– scutch (couch) / creeping bent/soft grass
List 4 Annual Broad leaved weeds:
– chickweed / cleavers / fat hen / charlock etc
List 3 Perennial Broad -Leaved weeds:
– docks / thistles / creeping buttercup
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?
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
What is chemical weed control in cereals: herbicide use a function of?
– resistance of crop to herbicide
– susceptibility of the weeds to herbicide
What does the resistance of the crop depend on? (3)
– type of crop and growth stage
– health and vigour of the crop
– dosage and correct application
What does the susceptibility of weeds depend on? (4)
– type of weeds and stage of growth
– condition of weed growth
– weather at spraying
– interaction with tank mix chemicals
Urea Herbicides MOA: (4)
Urea derivatives / IPU , Linuron, Methabenzthiazuron
Amides MOA:
Propyzamide
Nitriles MOA: (2)
HBN’s and Casoron
Triazines MOA : (3)
very soil persistent (simazine / atrazine / terbutryne)
Carbamates MOA(2):
– CIPC / IPC (Propham) phenmedipham (Betanal) , asulox
Anilides / Nitroanilines MOA (3):
Inhibitors / Metazachlor , diflufenican , pendimethalin
Thiocarbamates MOA:
Avadex
Organophosphorus MOA: (2)
Glyphosate , glufosinate
Sulphonyl Ureas MOA:
– Many, many products on market
Phenoxy Alkanoic acids: MOA
– Fops and Dins ( Fluazifop / Fenoxaprop etc )
Hormonal type herbicides: MOA
– Alkanoic acids
– Arylcarboxylic acids (derivatives)
– Urea herbicides
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?
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.
When choosing herbicides whats the 4 important things to remember:
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
One years weed is …
7 years seed
What sort of weeds will seed before harvest?
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
Whats a problem in Min-Till systems?
Widespread problems in mintil systems= Sterile Brome Control
