Thursday, November 26, 2020

Growers hold nerve amid another wet autumn

November 4, 2020 by  
Filed under Crops

Timing is everything for crops in the ground – and those yet to be drilled, says Richard Overthrow.

Although not as bad as last year, it has certainly been another frustrating autumn. At least there have been some drilling windows and most growers will have more winter cereals in the ground than at this point last year.

That said, there is also a significant acreage that will once again have to wait for spring to be drilled up, but we’re starting to get used to that, aren’t we?

Usually at this point we discuss latest safe sowing dates for winter cereals for those contemplating persisting with attempts to get these in the ground. But this is a less common approach now, given what we’ve learned from growing spring crops, in terms of management, rotational benefits and financial returns.

If winter wheat is sown this month grass weed pressure will be much reduced and for this reason, and considering the crop competitiveness issue, any residual herbicide treatments should not be stacked too heavily.

Too many products in a pre-emergence treatment can adversely affect crop establishment and ability to compete with weeds and as said these heavy inputs shouldn’t be needed anyway.

Early planting

Many growers rightly started cereal planting early, after last autumn’s experiences, so it is worth thinking about what these crops might be prone to. Diseases such as mildew and yellow rust can develop in strong, early sown crops in autumn.

A decent frost would take care of both but if such isn’t forthcoming action may be needed. Septoria will probably be evident in wheat but this never justifies autumn treatment. Barley diseases are more of a conundrum.

Net blotch in particular can develop in mild conditions on early sown barley crops and again, if the crop isn’t ‘shut down’ by cold weather then treatment may be needed, which in this case would not be cheap.

Cereal aphid control should be tailing off now. Any cereal crop emerging now, or later, is very unlikely to be infested so no treatment would be necessary.

Crops which emerged only recently but in time to attract migrating aphids might still reach the 170 day-degree threshold before winter starts but these crops should be inspected regularly and only treated if aphids are present.

Default position

In fact, this applies to any crop, even the early sown ones.

Any prophylactic insecticide use cannot be justified and with an increasing number of growers declaring their reluctance to use insecticides anywhere, the default position has to be no spray applied unless there is obvious justification.

So again, don’t simply spray as soon as 170DD is reached, use this as a trigger to go and look for something to treat.

As discussed previously, flea beetle pressure in oilseed rape was much reduced this autumn and even most of the later sown crops came through well. Any larvae in rape plants  should be obvious now and remember there are no effective control measures for larvae so do not attempt to treat with insecticides.

Again, however, numbers of these should be low compared to last season.

Soil temperature

This month soil temperatures usually become suitable for propyzamide applications, and if planned these would likely follow an early metazachlor-based treatment or post-emergence Belkar.

If propyzamide is the first herbicide to be applied the temptation might be to apply too soon, but it is definitely worth waiting for suitable soil conditions to get the best out of it.

Winter bean crops will have been sown last month and ideally weed control would have been done or at least started pre-emergence as post-emergence options are few.

Carbetamide is one such option, being a residual that can be applied post-emergence, but ideally before target weeds, especially grass weeds, become too large. Any bean crops not yet sown can go in any time this month or later but yield potential starts to fall off from now on.

Richard Overthrow is a regional agronomist with NIAB TAG, the UK’s largest independent agronomy organisation with several research centres in the Midlands. For more details, call 01223 342495.

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