Farm Ireland

Wednesday 22 November 2017

Smart weed control will pay dividends

With a little bit of care, cereal farmers can protect their slimming margins

Michael Hennessy

AS THINGS stand the economics of cereal farming is hanging on a knife-edge. Turning a profit has become increasingly difficult and every input must play its part to protect it.

Preserving this profit when using herbicides can be attacked from two ends -- by using them to increase or maintain yields, while reducing this input cost.

Herbicides are not the fastest rising input cost in cereals but they can play their part in reducing overall costs. Savings of €15-35/hectare are possible with a well-timed weed-control strategy versus an ad-hoc approach. Formulating a budget for herbicides used in spring cereals can be achieved quite easily with some basic knowledge of the weed spectrum in each field.

Excellent weed control can be achieved by all growers but some basic knowledge is required. In the same way that people memorise a football or rugby team from one to 15, with a few substitutes, knowing the top 15 weeds or so is also desirable when trying to control them.

Arguably the top 15 weeds in arable fields are:

1. Chickweed;

2. Charlock;

3. Knotgrass;

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4. Bindweed;

5. Cleavers;

6. Fumitory;

7. Speedwell;

8. Fat hen;

9. Orache;

10. Redshank;

11. Corn Poppy;

12. Red Dead nettle;

13. Hemp nettle;

14. Small nettle;

15. Mayweed.

The reserve players -- sorry, weeds -- are Nipplewort, docks, and thistles with wild oats, canary grass and annual meadow grass strong contenders.

Bring a picture of these weeds at various growth stages -- cotyledon, first pair of true leaves and adult plant -- with you when going walking crops and identify these weeds as you go. Pictures of these weeds can be found on the Teagasc client website. It's quite easy to identify these weeds if you employ a little patience in the field during inspection.

Deciding on the chemical to be used will be based on the chemical or combination of chemicals that will control the majority of weeds identified in the field. Timing the herbicide application is all important but it isn't everything. Crop density, sowing date and general growing conditions all impact on the success of weed control in cereals. It is fundamental to work with the growing conditions around the spraying timing to optimise weed control and reduce costs.

In a small demonstration on spring barley last year in Oak Park a herbicide test showed the value of early and late-application timings using different rates of herbicides. The first application was applied to half the plots when the crop was at early tillering stage. It was easy to see bare soil (see picture 1 -- far right, bottom) at this stage. The application was timed after a couple of very warm, humid and overcast days. The second application was applied roughly a month later at crop growth stage 31-32 (picture 2 -- right, top), again after a period of warm humid weather. Higher rates (half and full rates) of the same products applied at the first timing were applied at the second timing.

The visual and financial results of the demonstration were obvious for visitors to see at the open day some six weeks later. The plots sprayed early with the quarter rates were almost weed free and were cleaner than plots with full rates applied at the later timing. Also, plots receiving a half rate of herbicides at the early timings had the best control. The cost savings from the cheapest treatment, with good weed control, to the dearest treatment (full rates at later timings) were significant at €37/ha (€15/ac). The lessons from this demonstration and from similar replicated trials were that reduced rates will work well, but I have no doubt the weather conditions around the first herbicide application greatly helped the weed control.

Understanding the herbicides you are using is also necessary but you don't have to remember all the aspects of a chemical. Critically, there are a couple of key features you should know about herbicides -- the weeds the herbicide will control, the weeds it won't control and the weeds that it will partially control.

You'll see from table 1, right, that the application of a product will result in excellent control of many weeds, but the control of other weeds can be greatly increased with the addition of a hormone-type spray such as CMPP-P, MCPA etc.

Herbicide Choice

Sulfonylurea's (Ally Max, Cameo Max, etc) are the backbone for broad-leafed weed control in spring cereals. However, hormones are still needed to boost these chemicals to fill gaps in their susceptibility.

Increasingly, growers have little choice but to switch away from the standard mix containing Ally or Cameo, although generic forms of these products are still available. The range of herbicides available this year is very similar to last year, with products like Ally Max SX, Harmony Max SX, etc, widely available from merchants (see table 3, far right). These products offer good value for money as they contain up to 100pc more active ingredients for a slightly higher price over older straight products like Ally or Cameo.

The mixing and increased concentration of these SU actives into one product brings increased control to a broader range of weeds than using one SU product on its own. Due to the increased availability of products such as Ally Max SX, BiPlay SX and Harmony M Max these are now becoming the standard treatment in many spring crops and offer better insurance for fields where you do not know the weed history.

There is a tendency to use these in a similar fashion to the old products -- eg, reduce the rate to 80pc of a full rate. But as these products are more expensive, costs inevitably increase. Rates can be stretched in the correct circumstances to half rates or lower.

All the SU products have different strengths and weaknesses in terms of the control of weeds (table 1). Generally, SU should be mixed with a hormone-type product (CMPP-P, HBN, fluroxypyr or Dicamba) or Galaxy to achieve full control of a wide variety of weeds and to prevent weed resistance.

How to use the susceptible tables

Upon examination, a field predominantly contains chickweed, knot grass and charlock, with some ivy-leafed speedwells. The most appropriate SU would be Harmony Max SX but it will only give partial control of Ivy-leafed speedwell, therefore the addition of Foundation is necessary to fill the gaps giving good overall weed control.

Note on table 2,

Restricted range of herbicides for use on oats: Herbicides include Empire, Ally Express, Ally Max, BiPlay, Finish/Presite, Galaxy, Boxer, Oxytril CM, Stellox, Hobane, CMPP, MCPA, Eagle, Foundation, Hurler, Starane 2, Reaper and Tomahawk,

Tank mixing Ally Max or BiPlay plus CMPP is very popular and worked well in 2009. CMPP will give improved control of Fumitory, Cleavers, Fat hen and Orache. Fluroxypyr (Starane 2, Binder, Hurler, Reaper or Tomahawk) is the main active ingredient used for volunteer potato control. Alternatively GEX 353 (Calibre + Starane in a dual pack) is available and will give good control of volunteer potatoes including tuber cracking.

Irish Independent