Farm Ireland

Saturday 21 April 2018

Slow start to season will alter choices

With the wet weather, Michael Hennessy predicts that most crops will be planted later than normal.
With the wet weather, Michael Hennessy predicts that most crops will be planted later than normal.

Michael Hennessy

As I write rain continues to fall and the start of spring seems a long way off. Most spring crops will be planted later than normal as only about 10pc were planted up by the end of March.

A later sowing generally results in seeds being sown into a warmer seedbed. At the very least it has the potential to warm up faster with the longer days and stronger sunshine. Crops should emerge and get through the growth stages faster. One can argue the weeds may do the same, but crop competition and timeliness of herbicide application becomes all the more important in a season like this one.

However, many winter crops appear to be ahead of normal in outward growth stages, despite the cool and wet conditions. Will this unusual season affect the way we will control weeds this year?

One thing that winter cereal growers should be particularly careful with is herbicide selection, since more advanced growth stages restrict the use of many hormone-based products.

Crops that received a good autumn herbicide are relatively weed-free. This is probably a result of almost perfect conditions for the herbicides to control weeds from time of application up to the middle of December.

Met Éireann classified the autumn as warm, dull and dry in most places – three conditions that allow herbicides to work to their optimum.

However, even though general weed control is good, there are still fields where attention is needed.

All fields should be inspected for weeds in early spring. Bring your field records from previous years to guide you towards areas in the field that were troublesome in the past.

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One cleaver per square metre typically results in a 3pc yield loss, while wild oats at a population density of 3/msq will also knock 3pc off your final yield.

Other weeds, such as bindweed and knotgrass, are more troubling during harvesting.

At the other end of the spectrum, weeds such as groundsel are very uncompetitive, with 50 plants per square metre required to generate a 3pc yield loss.

However, it has the capacity to multiply quickly, so it also needs to be kept in check.

Many continuous winter cereal fields have high levels of cleavers due to the repeated application of similar herbicides such as IPU, DFF and Pendimethelin. These herbicides have a modest susceptibility rating for cleaver control.

Late germinating cleavers combined with a wet winter, where the herbicide is washed from the soil surface, tends to leave more uncontrolled cleavers in the spring. Research has shown over-wintered cleavers don't start to be competitive until the crop reaches growth stage (GS) 30. After this growth stage, cleavers compete with the crop by restricting light, depriving the crop of nutrients and ultimately reducing yield.

Overwintered cleavers can be difficult to control, especially when soil and air temperatures are low. Product choice includes Spitfire, Fluroxypyr (Starane 2, etc), Carfentrazone (in Ally Express), Eagle or CMPP.

All these products need the weed to be growing, but Spitfire, Eagle and Ally Express can be used at lower temperatures than Fluroxypyr or CMPP. Avoid using any product when temperatures are below 5C.

Rates need to be at least 60pc of a full rate for a large over-wintered cleaver, with higher rates where growing conditions are not great. CMPP will work best when temperatures are above 10C.

Indo Farming