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.
|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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