Release Date
06 October 2015

Release Date
06 October 2015

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Key Points

  • Glyphosate is more effective early.
  • Paraquat can be applied later than glyphosate.
  • Clover seed set can be reduced if sprayed during flowering.
  • Use ENHANCE® or ANTIEVAP® for spray topping.

Preventing seed set with a well timed spring herbicide application is an essential tool to reduce weed burdens – particularly for difficult to control in-crop weeds such as ryegrass, brome and barley grass.

To properly setup paddocks for a cropping phase, correct application timing and using the right herbicide with the right adjuvant is critical in getting complete weed set control.

Glyphosate and paraquat are the two main actives used for spray topping – the latter gives a good opportunity to rest glyphosate for resistance management and prevent the onset of resistance. They need to be applied at different timings, with glyphosate being more effective when used early and paraquat later.

The key advantage of using paraquat as a contact herbicide is that it can be applied later than glyphosate, when weeds have developed past the flowering or milky dough stage. Glyphosate requires time to translocate through the plant and therefore should be applied at seed head emergence prior to the dough stage (see Figure 1). This is useful for controlling barley grass which has a longer flowering period – but care should be taken when applying in flowering legume pastures. Seed set in legumes can be reduced significantly if spray topping takes place during early to mid-flowering.

Figure 1: Cereal grain at the soft dough stage.
Source: Agriculture Victoria

SACOA’s adjuvants ENHANCE® and ANTIEVAP® make effective tank mix partners for glyphosate and paraquat, improving their activity by decreasing drift while increasing leaf coverage and herbicide uptake into the plant.

Mineral oils, such as ANTIEVAP®, are particularly effective at reducing evaporation in warm conditions (>25°C).

With the recent launch of newer and easier to handle paraquat formulations, such as Gramoxone 360 Pro® from Syngenta, a number of independent collaborative trials have been conducted to assess the performance of SACOA’s range with these formulations. Results from this work will be published in the near future.

Key spray topping timings

Active (Rate gai/Ha) Key weed controlled & timing
Paraquat (100gai/Ha) Ryegrass – flowering heads in dough stage

Barley & Brome grass – post flowering in the dough stage

Silver Grass – prior to haying off


(110gai/Ha – 165 gai/Ha)

Ryegrass – during flowering when all tillers are in head

Barley & Brome grass – at seed head emergence prior to dough stage

Silver grass – early head stage


Source: Agriculture Western Australia


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This document should act as a guide only and no purchase or usage decisions should be made based on the information provided without obtaining independent, expert advice. SACOA and contributors do not necessarily recommend or endorse any products or manufacturers referred to. SACOA Pty Ltd will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information contained in this document. More information is available from SACOA via or 08 9386 7666, or by contacting your local reseller.
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