Straggle Muster 152 - 22/4/2005
A Cure for Nodding Thistles - Steve Bethell, Pasture consultant.
Are nodding thistles a problem on your property? If the answer is yes, then you're not alone!
I've lost count over the years of the number of frustrated comments from farmers who have spent a lot of hard earned money trying to control them and seem to be getting nowhere. This season has obviously been 'trying' to say the least. In my experience, the dreaded nodder is actually quite easy to control with herbicides. But when we throw clovers into the equation, the difficulty begins. 100% control in your established, permanent pasture and keeping your clover population is not easy and therefore a 'compromise' in your expectation of control needs to be accepted.
Firstly, in my experience, the best way to kill a nodding thistle is to let it grow, flower, set seed and generally its life is over. BUT aproximately 7000-8000 seeds per plant just went into the soil! Now you can see why so many properties have such huge weed seed banks and although no one is quite sure for how long the seed is viable, estimates of several decades are likely to be correct: About 10 per cent strike in the spring and 90 per cent in the autumn.
Prior to spraying we need to determine the size of the thistle and we need to look past the initial size of the beast growing on the surface of the soil. Basically I use my pocket knife ( or the spade's a lot easier to avoid the prickles) and cut it off at ground level to expose the crown of the root.
Looking down into the pasture, assess the diameterof the exposed root. ie. Is it a five cent, 20 cent or 50 cent piece size? As an indicative 'yard stick', I work on Soft Touch or Tropotox controlling upto a 20 cent piece size and Cleansweep or Thistlekillem controlling upto a 50 cent root crown diameter.
Anything larger or thistles with a multi crown root will require either a stronger chemical, such as Void but severe checking OR termination of your clover is inevitable. Whatever chemical is applied, a commitment to a follow up spot spray, grub or weed wipe programme in the spring is absolutely essential to tidy up any large thistles not controlled initially. Many ask me to clarify " exactly what is a multi crown nodding thistle?"
Simply, any nodder that has been mown, harmed by ineffective chemical applications or by animal hooves etc; the plant initiates a new shoot at the root crown, survives and becomes a very difficult to kill 'multi crowner'.
This can be seen best when exposed by the spade or a trained eye can identify them growing in the paddock.
The next step is to identify the age of the paddock. Basically, in new pastures I tackle the nodders very early, when the swards clover reach the two trifoliate leaf stage. An easy size to control and economical with the application of Tropotox or Soft Touch/ Cleansweep mixes but a warm ,12 degree C day is crutial in late autumn for these products to work successfully. If this stage is missed, then the percentage of control reduces significantly when tackling the larger and more aggressive weed at a later date.
For pasture swards (that include clover) which are older than 12 months, we can utilise the tougher Cleansweep or Thistlekillem (tough on red clover) options once the frosts begin. The aim is for the initial frosts to reduce the soil temperature and clover activity and therefore minimise the damage to our all important legume.
The key is to apply the correct rate of the correct chemical before the frosts 'burn' the thistle and then limits the chemical uptake. Once again, a warm day when applying is best. (Please feel free to contact myself if you would like to discuss the finer details on the dos and don'ts. Each situation varies and an individual recommendation should be sought before application commences)
A tip to remember when spraying your nodders is to always spray the fence lines. Many go to the hard work and expense of spraying the pasture, only to be reinfested later by the forgotten fenceline weed population! The seed travels approximately 25m on average.
The second tip is to include Kiwi Cover (spraying oil) with your herbicide to encapsulate the agrichemical, decrease spray drift, increase rainfastness, decrease drying time, prevent volatolisation of the phenoxy and is a high quality surfactant. In my experience I've found it improves the results for only a few extra dollars per hectare.
Often I walk over pastures that are about to be sprayed but see that the pasture is usually covering the target weed. At this time of the year, many are banking feed for the winter but the chemical needs to actually 'touch' the thistle. A quick graze to 'expose' the weed and then an opportunity to let 'freshen' for about 10 days is recommended. Some forward planning prior to spraying, really needs to start now.
Finally, you need to prioritise your goal. Do you want to control nodding thistles? Do you want to keep your clovers in an existing permanent pasture? To have both is difficult. If the nodding thistle population is huge and made up mainly of multi crowned plants, then spraying out and starting again with a complete pasture renovation should be considered in the spring. I suggest you then sow down a break crop and leave out the clovers and herbs so we can really tackle the weed problem without compromise. eg. Brassicas or short term grass.
Avoid soil disturbance wherever possible and deny the nodder any 'breathing space' with some form of ground cover. We all know that if you give them half a chance, they'll take it!
Don't give up. With a planned and logical programme and with some good ol' fashioned patience, you can win the battle! The time to spray is nearly upon us..
Until next time, best regards.
steve.bethell@xtra.co.nz.
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