IN A heavy land rotation of wheat, barley and then break crop, creeping thistles are an increasing problem. They are unaffected by residuals and emerge late in the spring. Is there anything to use other than Roundup?
R J Matthews,
Gunthorpe, near Oakham, Rutland
1 THERE are four main options in the cropping pattern you describe.
The most effective strategy is likely to be treatment with glyphosate (such as Roundup Biactive) in rotational set-aside. The best timing is when thistles are at or near flowering.
Treatment with glyphosate pre-harvest can be very effective, especially if the thistles are at or near flowering at the time of treatment.
Stubble treatments, such as with glyphosate to rosette stage are still the best option where adequate thistle growth is present. The thistles should be hit as soon as possible and growers should consider going back in.
Within growing crops at this time of year, there are recommendations for Dow Shield, Ally and MCPA in cereals. However, but the relative growth patterns of crop and weed cut-off timings for these products may mean there is not much of a target present before the latest permissible timings of these products. Shield also has a recommendation in oilseed rape before flower buds are visible but again there may not be much of a target.
To keep on top of thistles it will be important to take all opportunities if they arise. Although cultivation, especially in conjunction with an herbicidal approach, can help reduce numbers, the deep rooted nature of the weed makes this unpredictable.
ADAS Boxworth, Cambridge.
2THE cut-off for treatment with Dow Shield is at GS33 (third node) in wheat. Although thistles might be around at that time, they are more likely to come through later on. If you do have early thistles in cereals and there is a target there then it is a low-rate recommendation for Shield.
If treating wheat and barley, it is probably best to use Ally but in an oilseed or sugar beet break then the answer is to use Dow Shield which performs particularly well in broad-leaved crops and is a standard treatment for creeping thistle in sugar beet. The cut-off in oilseed rape will be at the green bud stage before it comes up above the canopy – effectively autumn or early spring treatments. Dow Shield is also cleared in linseed at a low 0.5 litre/ha rate.
The size of the root system in creeping thistle is what makes it such a problem. Growers need to consider specific products to keep on top of it in each year of the rotation.
Following crops may suffer a problem where growers have tried to patch spray the weeds in sugar beet but have missed a few round the edges of the patch.
Further information on Dow Shield use and recommended rates can be obtained from the technical hotline on 01462 457272
Dow AgroSciences, Hitchin, Herts.
3WE estimate about 15% of Ally sales are made for thistle control with applications going on at the end of May or beginning of June in tank mix with other products such as a flag leaf fungicide.
Ally can be used in wheat or barley up to GS39 but we find it is most effective against creeping thistle either at the early rosette stage of the thistle or later after stem elongation and at or before its flowering stage. This is because at the in-between stages – between GS31 and GS39 of the cereal crop – the thistles are growing rapidly with the crop and seem better able to overcome the effects of treatment.
We have looked at most of the sulfonylureas for control of creeping thistle, sow and other thistles, but Ally remains the most effective. Some growers put in additional wetters or adjuvants to increase penetration. We would say that is OK if you are using Ally as a stand-alone product but if it is being used with a fungicide or other products there is generally no need because there are sufficient wetters and adjuvants in the tank.
Ally + MCPA is another good mixture for early use only since the cut-off timing is GS32.
DuPont, Stevenage, Herts.
WE know, of course, that Justin McDonald is not a member of ACCS! However, if you are going to print pieces (Crops, w/e 10 April) that your readers will assume are genuine, then I am sure the reputation of your journal will not be enhanced by allowing some gross distortions of reality. Can I please provide you with some facts:
1. It is not possible "to throw away the ACCS renewal letter". No such letter exists and, therefore, cannot have been sent out.
2. ACCS renewals are effective from September 1999 – not July 1999.
3. In any event, someone joining last year got two harvests for the cost of our subscription – harvest 1999 is covered already.
4. By taking the schemes rules rather more seriously, the milling wheat would not have had dead insects in it – anyone who delivers grain in this condition deserves to get it rejected.
5. ACCS assessors do not give talks to NFU branch meetings – not, that is, in their capacity as a verifier.
To keep you up to date, I would confirm that the scheme has 8,200 members, farming just under four million acres. Whichever way you look at it, most wheat, barley and rape marketed from this harvest will have come from an ACCS farm.
T M Hughes, director, UK Food Quality Certification.
Editors note: Justin McDonald is currently indisposed after a bizarre accident with an overhead light fitting in his grain store. He will, however, be back on 8 May.