Summer Weed Control: The Tough Weeds (Milk Thistle, Prickly Lettuce, Wireweed & Fleabane)

One of the downsides to a lovely wet spring and wet harvest is it inevitably leads to some early summer spraying. Unfortunately, by the time…
December 12, 2022Ag Chem Back to All

One of the downsides to a lovely wet spring and wet harvest is it inevitably leads to some early summer spraying. Unfortunately, by the time the headers stop and the grain is out of the paddock, the summer weeds will already have some size and hardiness behind them. We will also be smack in the peak of Summer with hot and dry conditions (well, in a typical year anyway!) – which is not the easiest time to control weeds.


Farming wouldn’t be farming without challenges, and situations like this give us multiple hurdles to controlling even the easy weeds. So, what are our options for the tough weeds? Namely, those pesky fleabanes, wireweed, sow (milk) thistles, prickly lettuces and blanket weeds. All these weeds can germinate in late spring before harvest or even in winter. And after harvest, their growth really takes off when they start to see the sun. Leaving you faced with large and hardened weeds that the harvester has already cut off, which have grown a significant root system, and on top of that, have only a small leaf area for you to target. This makes controlling them with a single pass almost impossible. 


The solution: a double-knock approach.

Although it can be expensive and time-consuming, it is the only consistent approach to controlling the weeds mentioned above. 


So, what is a double knock? 

Simply put, it is 2 stage spray program set 7-14 days apart, with (most commonly) a glyphosate-based brew sprayed first, followed by a second spray pass of a paraquat-based brew* once sufficient time has passed for the glyphosate to translocate through the weeds (7-14 days). However, the second “knock” doesn’t have to be a herbicide. It can be heavy grazing by stock which will have similar efficacy to the paraquat spray. You want to ensure that your herbicide rates are appropriate; a couple of dollars extra per hectare can make all the difference in controlling a weed instead of slightly impeding it.  



Stock standard brews for tough weeds (but always check and get a spray reco for your unique situation): 


First Knock 

Glyphosate + 2,4D (Amine or Ester) + Metsulfuron/dicamba (Where applicable) + SOA & Li700 

(If using Amine, why not give Nufarm’s Dropzone a try? It’s a new, locally innovated 2,4-D technology that presents a range of benefits – including spray droplet optimisation, increased speed of action, low odour and a non-volatile formulation.)


Second Knock (Ideally 10-14 days later) 

Paraquat or Guerrilla* + Terrad’or & Hasten (optional) 

(Addition of Group 14 (G) will significantly improve the final weed kill, but not always necessary) 


Remember, apply herbicides in the best possible conditions and follow general summer guidelines:

  • Change over to Ultra Coarse nozzle for summer spraying (Very Coarse at minimum).
  • For glyphosate to affect actively growing weeds, they should be free from stress and dust.
  • Always try and target smaller weeds, and keep rates of glyphosate up on larger weeds or in stressed conditions.  
  • Target application in cooler morning conditions – HOWEVER, always be mindful of spray drift and inversion conditions. Avoid spraying around sunset and sunrise and in low wind conditions. Why not make it easy for yourself and sign up for the Mesonet?
  • If spraying 2,4-D, be especially mindful of conditions no matter where you are and use the correct nozzles. Remember – SUMMER spraying.
    • Sunset and sunrise 1 1/2 hour buffer
    • Ultra coarse nozzles
    • Move low – boom to 50cm above weeds.
    • Move slow – under 18km/hr.
    • Environment – avoid inversions, and check wind and weather.
    • Record all details.
  • Inversions can carry spray drift hundreds of kilometres, so even if they aren’t vines or susceptible crops around you, make sure to adhere to the guidelines. Also, check out Nufarm’s new Dropzone.
  • Paraquat is better in low light intensity conditions such as overcast, evening or night spraying. 


* You can only purchase and spray Paraquat products if you’re registered and have an up-to-date Chem Cert. 


For advice on your situation and what to spray this summer, please get in touch with one of our agro’s.