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Sunday 4 December 2016

Crunch time for effective weed control

Sort out these villains by the middle of the month or they'll start to be a threat to yields

Michael Hennessy

Published 12/04/2011 | 05:00

Control weeds, such as Charlock, at one pair of leaves
Control weeds, such as Charlock, at one pair of leaves

As many growers will testify, the coldest year in the past 40 -- 2010 -- had some effects on all crops, not least winter oats.

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Weeds are also subjected to the same conditions so there was a large winter kill of weeds, especially annual meadow grass.

At this stage of the year, most crops have received at least one herbicide, ranging from DFF + IPU or PDM + IPU or similar in the autumn. Spring applications ranged from an application of IPU as a holding strategy with a follow-up of a Fluroxypyr, to the likes of Cougar and Alistair.

Competitive weeds not controlled so far should be sorted by the middle of the month as competition by weeds, such as cleavers, after this stage will knock yield.

In the northeast, some growers are increasingly relying on Pacifica to do the heavy lifting of weed control in the spring. Pacifica offers excellent control of a broad range of weeds, including sterile brome, wild oats, annual meadow grass and soft broad-leaved weeds. However, it tends to be weaker on cleavers, bindweeds and knotgrass. In addition, a strategy that relies heavily on an ALS-type product to control all weeds will increase the likelihood of building ALS-resistant populations in the field.

If this happens, weed control will then be more expensive in these fields. Use a herbicide with another mode of action before or after Pacifica, to reduce the risk of building up ALS-resistant weeds.

Broadway Star is new to the market this year. This herbicide will prove a useful addition to winter wheat weed control. The product boasts an impressive array of weeds that it will control, including rye-grass, soft brome, sterile brome, wild oats, cleavers, poppy, pansy, common field speedwell, ivy-leaved speedwell, charlock, volunteer rape and mayweed. The addition of an adjuvant, such as BioSyl, is recommended.

Broadway Star can be applied up to growth stage 32. Its only obvious weakness is the lack of annual meadow grass control and the fact it is classed in the ALS inhibitor stable of herbicides, which may be an issue with certain resistant varieties of weeds.

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Wild oats

The herbicide options for wild oat control are a little narrower this year, with Puma Extra no longer available and changes to Cheetah Super. Firstly, use up any Puma Extra in the store this year before using other wild oat chemistry, as after this year it will not be cleared for use.

Cheetah Super will also not be available this year, so again use up existing stocks. Cheetah has changed its colours and is now called Cheetah Extra.

The product has increased the level of actives but the product maximum user rate has been lowered from 1.25l/ha to 1l/ha. Axial will continue to dominate the market this year as its flexibility in the tank makes it suitable for most situations.

Sulfonylureas (SU), such as Ally Max or Cameo Max, are all ALS herbicides and are the backbone for broadleaf weed control in spring cereals. However, hormones and others such as Galaxy and HBN (Oxytril) are still needed with SUs to fill gaps in their weed control spectrum.

Although some straight products, such as Finy, Empire and Thor, are available the majority of growers have switched to products with mixes of actives such as Ally Max SX or Harmony Max SX, which are widely available from merchants. These products offer good value for money as they contain up to 100pc more active ingredients for a small increase in price over older, straight products such as Ally or Cameo.

Concentration

The mixing and increased concentration of these SU actives in one product brings increased control of a broader range of weeds than using one SU product on its own. Many of these products have become standard treatment in spring crops and offer better insurance for fields where you do not know the weed history.

There is a tendency to use these products in a similar fashion to the old products by reducing 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 (see table 1, below right). Generally, SU should be mixed with a hormone-type product such as CMPP-P, HBN, Fluroxypyr or Dicamba or Galaxy to achieve full control of a wide variety of weeds and to prevent weed resistance.

Indo Farming