Cereals 2024 Weed Control Part 2 Herbicide Use and Pesticide Resistance

Question 1

What are key active ingredients in widely used herbicides?

Answer 1

• Mesosulfon-methyl (Alister / Pacifica)
• Diflufenican (DFF / Alister / Firebird )
• Iodosulfuron-methyl (Hussar/Alister / Pacifica)
• Pedimethalin (PDM / Flight (Crystal )
• Sulphonyl-Urea’s (SU) many of
• Hormonal (CMPP / MCPA)
• Fluroxypyr (Starane / Hurler / Reaper,
• Ioxynil, bromoxynil (HBN’s)
• Isoproturon (IPU)

Question 2

Isoproturon (IPU) use in winter cereal crops

1- What is it and whats it used on?

2- Whats grass weed control based on?

3- Whats it available under, what names?

4- What country have big problems with IPU’s?

5- What was it banned in Ireland ad EU?

Answer 2

1- a residual soil-acting herbicide with activity on grass weeds and broad-
leaved weeds

2- Grass weed control was based on the use of IPU before tillering of
the grass / some b/l weeds, historically was useful for wild oats control

3- availiable under a range of brandnames - Arelon, Fieldguard,
Tolkan, but mostly used in a product which is a formulation
with other a.i.’s

4- In UK IPU had big problems with leaching into waterways and
was banned 15 years ago

5- In Ireland and EU - banned from 2017 onwards

Question 3

1- What is DFF?

2- What does Diflufenican go into?

3- When is pre and post emergence on winter wheat and barley?

4- What is resistant ?

5- What are the new, high activity products alternatives?

Answer 3

1- Is a residual soil-acting herbicide with
good activity on broad-leaved weeds and useful
grass weed activity

2- Diflufenican goes into tank mix combinations

3- end-Sept. to early-March

4- fumitory is resistant (also resistant to Ally)

5- new high activity products alternatives are
Firebird & Alister

Question 4

What are the 2 current options for weed control in winter cereals?

Answer 4

Firebird

Alister

Question 5

What is Firebird?

Answer 5

is a residual soil-acting herbicide with
activity on grass weeds and broad-leaved weeds

– DFF + flufenacet (400+200 g/l) with a recommended
rate of 0.3 l/ha
– Early post-emergence on winter wheat and barley
– Very good on annual meadowgrass (AMG)
– Weakness on cleavers, charlock

Question 6

What is Alister?

Answer 6

is a post-emergence herbicide for GS 13 to 30
and is broadspectrum with strength on AMG

DFF + mesosulfuron + iodosulfuron with a rate of 0.75-
1.0 l/ha

Question 7

Whats a good spraying technique for small grass weeds?

Answer 7

IMPT
Correct spraying technique is very important
- Boom height

Question 8

What optimizes the performance of herbicides?

Answer 8

• Product choice / Formulation Important but …..
• Sprayer in good working order and properly calibrated
• Nozzle Choice
• Reducing water volumes can improve timing
• Boom Height 50cm above target for 110 fan nozzles
• Forward Speed determined by keeping boom level

Question 9

One years weed is…

Answer 9

7 years seed

Question 10

Sterile Brome Control Options:

1- Where is this a widespread problem?

2- What is the problem in achieving?

3- What is broadway star mix?

4- What does it work on ?

5- What is use ideal?

6- What other weeds does it have a good spectrum on?

7- What is sterile brome control options weak on?

Answer 10

1-In min-till system

2- Problems with achieving high level of control 99%

3- Broadway Star (pyroxsulam + florasulam) in a granule
formulation

4- Contact only action so only works on weeds present so
use medium to fine nozzles and an adjuvant

5- Early-autumn use is ideal but also in spring – up to GS
32 (less efficacy)

6- good spectrum on other weeds – wild oats, ryegrass

7- Weak on AMG (need pendimethalin mix)

Question 11

1- What is a very important and big problem in cereal crops?

2- How fast can weeds multiply?

3- Is it a competitive weed?

4- Is it expensive to control with herbicides?

Answer 11

1- Wild oats are a very important
weed in cereal crops

2- Weed can multiply very fast x
100+ in two years

3- it is a very competitive weed
with the crop - reduces yield
and quality

4- expensive to control with
herbicides – Axial Pro at rates
from 0.6 – 0.85 l/ha

Question 12

What is the target plus control for wild oats?

Answer 12

99%

Question 13

Common weeds in Winter crops: (7)

Answer 13

• chickweed
• speedwell
• mayweed
• cleavers
• red deadnettle
• fumitory
• field pansy

Question 14

Common weeds in Spring Cereals (6)

Answer 14

• chickweed
• speedwell
• fat hen
• red shank
• knotgrass
• corn marigold

Question 15

1- Spring weed control in cereal crops:
Soft weeds?

2- Key “different” weeds are ?

Answer 15

– ‘soft’ weeds in good growing conditions with wider
‘window of opportunity’ to spray in suitable
weather conditions

– opportunities to reduce herbicide rates alone and in
mixture : typical cost is Euro 15-30/ha

2- key ‘different’ weeds are the polygonum weeds

Question 16

If you get a question on tillage practices half your anwser is on weed control

Question 17

Reduced herbicide rates alone and in mixture costs how much for spring weeds?

Answer 17

typical cost is Euro 25-35/ha

Question 18

What is herbicide use dominated by?

Answer 18

sulphonyl urea’s

Question 19

Herbicides are typically applied when? in Spring cereal crops:

Answer 19

typically
applied before the end of
tillering (GS 30)

Question 20

Using sulphonyl urea herbicides in practice :
Ally / Cameo / Harmony / Calibre

Advantages: (5)

Answer 20

• excellent spectrum
• good performance where rates are reduced to 50- 75% of R.Rate
• excellent activity on previously difficult annual and perennial B/L weeds
• low dose rates 15-30 g/ha
• granule and tablet
  formulations
• wide window of appl. up to
  flag leaf on all cereals
• very compatible with other
  crop protection products
• low mammalian toxicity

Question 21

What are disadvantages in using sulphonyl urea herbicides in practice :
Ally / Cameo / Harmony / Calibre

Answer 21

• sprayer contamination
• sensitivity of brassicae crops
  to 1/70 of rate
• recent emergence of resistant
  weeds - chickweed, marigold

Question 22

What are second generation SU herbicides?

Whats Issues with them?

What are key products?

Answer 22

More focussed spectrum targeting the control
of blackgrass, annual meadow grass, sterile
brome, cleavers etc

• Issues with resistance management strategies
• Key products
  – Atlantis (UK) for blackgrass
  – Alistar/Pacifica/Hussar for AMG / wild oats
  – Pacifica and M for sterile brome control
  – Eagle for cleavers control

Question 23

What are 4 symptoms of herbicide resistance?

Answer 23

– Healthy plants beside dead plants of the same
species
– Poor control of one susceptible species when
other species are well-controlled
– Discrete weed patches
– Gradual decline in control over several years

Question 24

Is herbicide resistance inherited?

Answer 24

Herbicide resistance is an inherited trait and
with repeated selection resistant plants
survive, multiply and dominate the weed
population

Question 25

What are the 2 main R mechanisms? **

Answer 25

– Enhanced Metabolism – herbicide
detoxification (partial R)

– Target-site resistance – the site of activity of the
herbicide is blocked (total R) SU’s

Question 26

Whats the 6 risk factors of herbicide resistance ?

Answer 26

• Continuous winter/spring cereal cropping
• Continuous non-ploughing
• Totally depend on herbicides
• Use the ‘same’ herbicides
• Have high weed levels
• Evidence of herbicide R on farm / in general
  area

Question 27

List examples of ‘Excessive’ Herbicide Use in Ecotillage-
based Continuous Winter Wheat Production (6)

Answer 27

1. Glyphosate on the stale seedbed (Sept)
2. Pre-emergence Stomp (Oct)
3. Autumn post-emergence (Dff / SU) (Nov)
4. Spring (reduced-rate) (Apr)
5. Spot spray (Sterile brome control) (May)
6. Pre-harvest Glyphosate (July