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Control weeds in late spring crops

The delayed sowing of the majority of spring crops will result in a shorter growing season this year. Consequently, once crops get established, they will race through the development phases quicker and growers will need to be alert so that crop inputs are applied at the correct stage.

Weed control strategies have not changed much over the past 15 years as almost no new actives have been introduced.

The reliance on these few products has given growers confidence, but Mother Nature has also enjoyed this predictability and reacted by developing resistance in some weed species to some herbicides. This will be discussed later.

Sulfonylurea (SU) products such as Ally Max and Cameo Max, are ALS herbicides and are the backbone of broad- leaf weed control in spring cereals.

These products have become the standard treatment in spring crops and offer a wider weed spectrum for fields where you don't know the weed history.

There is a tendency to use these products in a similar fashion to the straight products, eg reduce the rate to 80pc of a full rate.

However, as these products are more expensive, using higher rates inevitably increases costs. Rates can be stretched in the correct circumstances to half rates or lower.

Straight products such as Thor, Empire, Lorate and Rebel are available and will work well in targeted circumstances.

Generally, the SU products have weed control gaps and should be used with hormones herbicides and others like Galaxy, Foundation and HBN (Oxytril, etc).

Mixing these products is also desirable to keep weed resistance at bay.

Table 1 outlines some of the strengths and weaknesses in many of the available products.

Winter wheat

General weed control in most winter crops was completed in early spring this year. However, some growers may have to come back to control some of the more problematic weeds such as cleavers, fumitory, groundsel, poppies and docks.

In terms of competitiveness, cleavers have the largest yield reducing effect. But control of the other weeds is necessary each year to keep the background population to a minimum.

Cleavers not controlled so far should be controlled by growth stage (gs) 30 of the crop, as competition after this stage will reduce yield.

Options such as Boxer, Eagle and Fluroxpyr can be used to control cleavers, whereas some of the SU herbicides (Ally Max, Cameo Max etc) should be used to control groundsel, poppies and docks.

Other herbicide alternatives (with a wide weed spectrum) include Pacifica and Broadway Star.

Pacifica offers excellent control of a broad range of weeds including sterile brome, wild oats, annual meadow grass and soft broad leaved weeds but tends to be weaker on cleavers, bindweeds and knotgrass.

Broadway Star will control rye grass, soft bromes, sterile brome, wild oats, cleavers, poppy, pansy, common field speedwell, ivy leafed speedwell, charlock, volunteer rape and mayweed.

The addition of an adjuvant (BioSyl) is recommended.

Broadway Star can be applied up to gs 32. Its only obvious weakness is the lack of annual meadow grass control.

Irish Independent