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Weeds

Weed Control

The following are main points you should consider before applying a herbicide:

  • Spray early at the 3 - 5 leaf stage for successful weed control in spring cereals.
  • Reduced (½) rates have been successful in Teagasc trials where the weeds were actively growing and at an early growth stage.
  • To maximise the uptake of herbicides (important when using reduced rates) the weeds need to be actively growing for 3-4 days before spraying.
  • By delaying Broad Leaved Weed (BLW) control until GS 30/31 you may loose yield potential from early weed competition.
  • Timing: There are numerous herbicides available which can be applied from the 2-3 leaf stage to flag leaf.

spring-barley-weed-trials-graph

Crop StageHerbicides
2-3 leaves to flag leaf Empire/Finy/Lorate/Rebel, Ally Max, Cameo Max, Calibre Max, Harmony Max, BiPlay, Thor, Eagle, Spitfire.
Fluroxypyr (various)
2-3 leaves to second node Ally Express, Hussar
2-5 leaves to first node CMPP, Foundation, MCPA, Undersown products

 

The water: The quality of water can affect the efficacy of herbicides however herbicide formulations are optimised to overcome most of these difficulties. Where water quality is suspected then the addition of adjuvant (e.g. water conditioner or non-ionic wetters, etc.) can help.

The sprayer: Uneven application as a result of worn or blocked nozzles can result in poor weed control especially if conditions are not ideal. Nozzle selection can also affect the eventual outcome. Generally, as standard, sprayers are fitted with a 025-04 flat fan nozzle. In most situations these nozzles are robust enough to apply a herbicide in the correct droplet size to get good control. The calibration of the sprayer using these nozzles is vital to ensure the herbicide is applied at the correct water volume and spray quality.

The weeds: Correct identification of size and type of target weeds in a field is essential. Generally weed control in spring cereals should be completed by early tillering stage of the crop. At this stage weeds will not have passed the two true leaf stage. In good growing conditions rates of herbicides can be reduced.

The weather: Growing conditions before application of a herbicide are more crucial than after the herbicide has been applied. During a cold spell growth slows and plants build a waxy layer on the leaf surface. During a rapid phase of growth plants leaves expand, new growth develops and the waxy layer narrows. Herbicides landing on a weed have to pass the waxy layer before entering the plant. The thicker the waxy layer the less herbicide will enter the plant.

The timing and rates of herbicides is critical to successful weed control. The following are some points to be taken into consideration before applying the herbicide.

 

The timing and rates of herbicides is critical to successful weed control. The following are some points to be taken into consideration before applying the herbicide.

 

Table 1

 
 Ally MaxCalibre MaxCameo MaxHussarCMPPCMPP+
Dicamba
Galaxy
Black Bindweed MR MS S   -- MS S S
Charlock S S S S S S S
Chickweed S S S S S S S
Cleavers R MS MS S S (S) S
Corn Marigold S MS S MS R R (S)
Fumitory MR*** MS* S* R MS S (MS)
Knotgrass MS** S* MS** MS MR S (S)
Poppy S S S -- MR MR MS
Red Deadnettle S S S S MS MS MS
Speedwell Common  S S MS S MS MS R

 

Weed Resistance

Resistant weeds continue to increase across arable fields and need careful management and follow-up field visits to monitor their control.

Tank mix alternative chemistry with ALS-herbicides as an anti-resistance strategy

Resistance WeedResistant toSuggested partner product for control
Chickweed ALS$ CMPP-P or fluroxypyr
Poppy ALS$ MCPA
Corn Marigold* ALS$ HBN, Clopyralid, IPU

**ALS-resistant marigold needs to be controlled at 2 leaf stage for reliable control.
$ALS herbicides include: Ally Max, Eagle, Florasulam (in Spitfire), and Pacifica etc.

  • Increase the rate of the Non-ALS partner product if resistance is suspected.
  • Re-assess weed control 2-4 weeks after spraying.
  • Follow up with an appropriate product to reduce the resistant weed becoming dominant.

A brief summary of Teagasc experiments on ALS-resistant chickweed is available at this link , page 107